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OCR 21st Century Science: C6 Chemical synthesis

COLLINS NEW GCSE SCIENCE © HarperCollinsPublishers Ltd 2011

C6 Module Introduction

Pages 162−163 in the Student Book provide an introduction to this module.

When and how to use these pages

These pages summarise what students should already know from KS3 or from previous GCSE units and provide

an overview of the content that they will learn in this module.

o Use these pages as a revision lesson before you start the first new topic.

o Brainstorm everything that students remember about the different topics using the headings as a starting point. Compare your list with the points on page 162.

o Use the questions on page 162 as a starting point for class discussions.

o Ask students if they can tell you anything about the topics on the right-hand page.

o Make a note of any unfamiliar / difficult terms and return to these in the relevant lessons.

Suitable answers to the questions on page 162 are:

o No, everything is made up of chemicals.

o Sodium ion, Na+, chloride ion, Cl

–, (and hydrogen ions, H

+, and hydroxide ions, OH

–).

o Burning magnesium in air or oxygen to form magnesium oxide. Two atoms each of magnesium and oxygen.

You could revisit these pages at the following point:

o before lesson c6_07 on energy changes in reactions, pages 176−177

Overview of module

Students begin by learning about the chemical industry and the steps in the process of synthesising a new

substance.

Then they go on to learn about the properties of acids and alkalis in neutralisation reactions, including how to carry

out a titration, and find out how to calculate the amounts of substances involved in reactions using relative atomic

masses. They also study the energy changes in reactions and methods of separating and purifying substances.

This is followed by measuring the rate of chemical reactions and investigating the effect of changing the conditions

of a reaction, including the use of catalysts.

Finally students apply the ideas covered in the module to consider the synthesis and manufacture of a chemical

product.

Obstacles to learning

Students may need extra guidance with the following terms and concepts:

Internet research

Data on the chemical industry given in websites can be difficult for students to understand and interpret. Examples

need to be chosen carefully.

Acids, alkalis and salts

Recalling a long list of names of substances can be difficult unless they are related to observations or other facts.

The number of possible combinations of acids and salts make it difficult for some students to recall all the formulas

required by the specification.

The names of most acids do not reveal that they contain hydrogen, and many students have difficulty in

remembering to change the ending from the acid to the salt.

Reacting masses

Some students will have difficulty handling the ratios of reacting quantities.

Titration

Carrying out titration requires considerable manual dexterity and coordination. Students need time to become

familiar with handling the apparatus and to build up skills.

C6 Module Introduction continued


Energy changes in reactions

Students will have met the use of reactions as an energy source (e.g. combustion) but it can be difficult to

appreciate that the reactants of such reactions are themselves losing energy.

Purification

The use of the term ‘pure’ in everyday language can lead to misconceptions. Understanding the reasons for the

many steps in a purification process can be confusing.

Rates of reaction

Most students can appreciate the difference between fast and slow reactions, but can find calculating rates difficult

if they have limited familiarity with graphs – particularly non-linear relationships.

The organisation of the practical work for this topic can overwhelm the learning of the effects of changing factors on

rates of reaction and the explanations. It is important to find time for discussion of the ideas as well as collection of

data.

Catalysts

Students may think that a catalyst, such as the platinum in a catalytic converter, is just a convenient place for the

reaction to occur and not understand that the atoms of the catalyst are actively involved in the reaction.

Practicals in this module

In this module students will do the following practical work:

o investigating combustion and oxidation reactions (demonstration)

o identifying acids and alkalis and measuring pH

o reactions of acids

o making a salt and calculating masses

o acid–alkali titration

o investigating neutralisation by an ‘antacid’

o exothermic and endothermic reactions (demonstration)

o measuring temperature change in a reaction

o purifying sodium chloride or copper sulfate

o fast and slow reactions (demonstration)

o using different methods to measure the rate of reactions

o investigating factors that affect the rate of reaction

o investigating the effect of a catalyst on reaction rate

o planning a method to synthesise a salt

Key vocabulary covered in this module

�� chemical synthesis

�� indicator �� acid �� alkali �� pH scale

�� salt

�� formula �� relative formula mass

�� neutral �� neutralisation �� end-point �� titration �� range �� variation �� true value �� outlier �� mean

�� ionic equation

�� exothermic �� endothermic �� energy level diagram �� heat exchanger

�� pure �� filtration �� dissolving �� filtrate �� evaporation �� crystallise �� dessicator

�� rate of reaction

�� concentration

�� catalyst �� catalytic converter



C6 Analysing, evaluating and reviewing

Pages 180−181 in the Student Book prepare students for controlled assessment.


This activity provides an opportunity to build and assess the skills that students will use when evaluating an

investigation and reviewing results alongside secondary data.

Ask students to:

o read through the context and tasks, listing any terms that they do not understand

o as a whole class or in small groups, discuss the tasks to ensure that all students understand the terminology used and to clarify what is required

o work individually or in small groups to answer the questions for each task.

If time allows, ask the students to mark one another’s work using the mark scheme provided.

Notes

This activity gives students the opportunity to analyse and evaluate a set of data from a series of experiments to

make a salt and test a hypothesis. Students have to make judgements about the reliability and usefulness of the

information provided.

Answers Task 1

� About the same.

� Difficult to say; the carbonate seems to give higher yields but is impure.

Task 2

� Metal 72–76%, oxide 80–84%, carbonate 86–90%

� Carbonate is highest, metal the lowest, no overlap (4% spread for each)

Task 3

� The metal and carbonate samples contained impurities as they predicted, but it is not certain that the oxide

gives the best yield.

� They suggested that magnesium also reacts with water to form magnesium hydroxide, and that excess

magnesium carbonate dissolves, both contaminating the magnesium chloride.

Task 4

� Not very – no data provided to show that measurements were repeated.

� The ranges are quite small and do not overlap so they suggest that results obtained for each reactant are

reliable.

� The purity of the samples, in particular the amount of magnesium carbonate present in samples from Groups F,

G and H.

C6 Analysing, evaluating and reviewing continued


Mark scheme

For grade E, students need to:

o Compare the similarities and difference of their results with a result from one other source.

o State where they got the secondary data from.

o Comment on whether the patterns in the data support their prediction or hypothesis.

o Use some scientific terms correctly.

For grades D, C, in addition they need to:

o Use a range of secondary sources which are referenced correctly.

o Describe and explain how the secondary data supports or undermines their data.

o Explain how their hypothesis can account for the patterns in the data or suggest how their hypothesis should be altered.

o Write a report using scientific terms and generally correct spelling, punctuation and grammar.

For grades B, A, in addition they need to:

o Discuss how confident they are about the accuracy of the data used.

o Comment on similarities and differences in the data.

o Describe in detail what further work could be done to make them more confident of their hypothesis.

o Write a comprehensive and logical report using scientific terms and with very few spelling, punctuation or grammatical errors.



C6 Exam-style questions

Pages 192–193 in the Student Book are exam-style questions.


These questions are based on the whole of Module C6 and cover a range of different types of questions that

students will meet in their written exams.

o The questions could be used as a revision test once you’ve completed the module.

o Work through the questions as a class as part of a revision lesson.

o Ask students to mark each other’s work, using the mark scheme provided.

o As a class, make a list of the questions that most students did not get right. Work through these as a class.

Notes on the worked example

The question is about energy changes and rates of reaction.

In part (a) students have to decide whether the conclusions drawn from a set of results are correct and justified.

This requires both knowledge and judgement.

Part (b) involves the recall of knowledge of energy level diagrams applied to the specific example of the question.

Part (c) also requires recall of knowledge but the last question requires a judgement related to how scientists

announce the results of their work.

Assessment Objectives

These exam-style questions cover the Assessment Objectives as described below.

Assessment Objectives Questions

AO1 Recall, select and communicate their knowledge and understanding of science

1a, 1b, 2, 3a(i), 3b, 4a, 4b, 4c

worked example, a, b, c(i)

AO2 Apply skills, knowledge and understanding of science in practical and other contexts

1c, 2, 3a(ii), 3a(iii), 4d(ii)

AO3 Analyse and evaluate evidence, make reasoned judgements and draw conclusions based on evidence

4d(i), 4d(iii)

worked example a, c(iii)

Answers

These answers are also supplied on the Teacher Pack CD so that students can mark their own or their peer’s work.

Question

number

Answer Additional notes Mark

1a Hydrogen chloride 1

1b 4 1

1c Sodium carbonate + sulphuric acid →

sodium sulphate + water + carbon dioxide

1 mark off for each mistake to a

minimum of 0

2

2 Relevant points:

Controlled variables – volume and

concentration of acid, mass of carbonate,

temperature

Method of measuring amount of carbon

dioxide released (volume or mass)

For 5–6 marks:

Answer provides all the relevant

details of an appropriate method,

including the controlled variables and

an explanation of the theory (referring

to collision frequency). All information

is relevant, clear, organised and

6

C6 Exam-style questions continued


Reaction timed

Repeated for different size pieces of carbonate

Repeat results obtained

Reactions occur when particles collide

Smaller pieces mean more particles exposed

on surface/ greater surface area

Smaller pieces have a greater collision

frequency

presented in a structured and coherent

format. Specialist terms are used

appropriately. Few, if any, errors in

grammar, punctuation and spelling

For 3–4 marks:

Answer provides a suitable method

with at least one controlled variable

and shows some understanding of the

theory. For the most part, the

information is relevant and presented

in a structured and coherent form.

Specialist terms are used, for the most

part appropriately. There are

occasional errors in grammar,

punctuation and spelling

For 1–2 marks:

Answer gives some suggestions for a

method, but the explanations are

missing or incorrect. Answer is

simplistic. There is limited use of

specialist terms. Errors of grammar,

punctuation and spelling prevent

communication of the science

3a(i) Aqueous/ dissolved in water 1

3a(ii) 2 1

3a(iii) RFMs: MgO = 40, MgCl2 = 95

Equation shows that 40 g of MgO will make 95

g of MgCl2. So, 4 g of

4 g of MgO will make (4/40) × 95 =

9.5 g of MgCl2

1 mark for correct method with

working shown but incorrect answer

2

3b D-F-B-A-C-E 3

4a 20cm3 pipette 1

4b H+(aq) 1

4c Swirl the mixture

Stop when the indicator changes colour

permanently

Repeat readings

All three for 2 marks

Any two for 1 mark

2

4d(i) Yes; it is significantly different from the other

results

He has repeated the experiment a number of

times, so it can be left out of calculations

1

1

2

4d(ii) RFMs: NaOH = 40, HCl = 36.5

The equation shows that 40 g of NaOH will

react with 36.5 g of HCl, so 4g of NaOH will

react with (4/40) × 36.5 = 3.65 g of HCl

Therefore 20 cm3 of NaOH solution will

neutralise 20 cm3 of HCl solution

2 marks for a complete and logical

explanation

1 mark if an important step is left out

2

4d(iii) The mean of the results is 20.0 cm3 [(19.1 +

20.0 + 20.1) ÷ 3]

This matches the predicted volume of

hydrochloric acid required – confirming that the

concentration of sodium hydroxide is correct

1

1

2



C6 Module Checklist

Pages 190–191 in the Student Book provide a student-friendly checklist for revision.


This checklist is presented in three columns showing progression, based on the grading criteria. Bold italic means

Higher tier only.

Remind students that they need to be able to use these ideas in various ways, such as:

o interpreting pictures, diagrams and graphs

o applying ideas to new situations

o explaining ethical implications

o suggesting some benefits and risks to society

o drawing conclusions from evidence they have been given.

These pages can be used for individual or class revision using any combination of the suggestions below.

o Ask students to construct a mind map linking the points on this checklist.

o Work through the checklist as a class and note the points that need further class discussion.

o Ask students to tick the boxes on the checklist worksheet (on the Teacher Pack CD) if they feel confident that they are well prepared for the topics. Students should refer back to the relevant Student Book pages to revise the points that they feel less confident about.

o Ask students to use the search terms at the foot of the relevant Student Book pages to do further research on the different points in the checklist.

o Students could work in pairs, and ask each other what points they think they can do, and why they think that they can do those, and not others.

C6 Module Checklist continued


Module summary

In the introduction to this module, students were presented with a number of new ideas. Work through the list

below as part of their revision. Ask students to write their own summaries and mind maps, using this list as a

starting point.

The chemical industry

o The chemical industry provides us with many useful products, for example food additives, fertilisers, dyes, paints and medicines.

o There are many stages in the industrial synthesis of a chemical compound, including choice of reactants and their quantities, deciding on the reaction conditions, assessing the risks, separating and purifying the product and determining the yield.

o There are hazards in using chemicals and particular precautions need to be taken.

Acids and alkalis

o Acids react with many metals to form a salt and hydrogen gas.

o Acids react with metal oxides and hydroxides to form a salt and water.

o Acids react with metal carbonates to form a salt, water and carbon dioxide gas.

o Salts are ionic compounds.

o Relative atomic masses can be used to calculate the masses of reactants and products in a reaction

o Neutralisation reactions involve acids and alkaline substances reacting together.

o When an acid reacts with a hydroxide, a salt and water are formed. The hydrogen ions from the acid join with the hydroxide ions to form water.

o Titration is a technique used to determine the volumes of acidic and alkaline solutions needed for neutralisation.

Energy changes

o A reaction that gives out heat is termed exothermic.

o A reaction that takes in heat energy from the surroundings is termed endothermic.

Separating and purifying

o A pure substance has nothing else mixed with it.

o Dissolving, filtering, evaporating and crystallising are ways of purifying a substance.

o The percentage yield of a reaction is:

[actual yield (from experiment)] ÷[ theoretical yield (from the reaction equation)] × 100%

Rates of reaction

o The rate of a reaction is the change in quantity measured (e.g. amount of product) in unit time. It can be found by a graphical method.

o The more collisions there are between particles of reactants, the greater the rate of reaction.

o The rate can be increased by increasing the temperature, increasing the concentration of reactants, or decreasing the particle sizes.

o Catalysts are substances that speed up a chemical reaction but are not used up themselves.

o In industry it is important to control the rate of a reaction.



Checklist C6 Aiming for A

Use this checklist to see what you can do now. Refer back to pages 164–189 if you’re not sure. Look across the rows to see how you could progress – bold italic means Higher tier only.

Remember you’ll need to be able to use these ideas in many ways:

� interpreting pictures, diagrams and graphs � applying ideas to new situations � explaining ethical implications � suggesting some benefits and risks to society � drawing conclusions from evidence you’ve been given.

Look at pages 300–306 for information about how you’ll be assessed.

Working towards an A grade

Aiming for Grade C �� Aiming for Grade A �� recall hazard symbols and give precautions for handling hazardous chemicals

identify the stages in the synthesis of a chemical compound

interpret data from various sectors of the chemical industry

recall the use of indicators to test for acidity and alkalinity

recall some solid, liquid and gaseous acidic substances and some common alkalis

recall the use of universal indicator and pH meters to measure the pH of a solution

recall the formulae of the reactants and products of some of these reactions

interpret balanced chemical equations including state symbols

work out the formula of salts given the charge on the ions and work out the charge on an ion given the formula of the salt and the charge on the other ion

understand that a balanced equation shows the relative number of atoms of each element in the reactants and products; substitute relative formula masses and data into a given mathematical formula to calculate the mass of a reactant or product

use balanced equations and given data to calculate the mass of reactants or products in a reaction

recall that the reaction of an acid with an alkali is a neutralisation reaction; describe how to accurately carry out a titration

interpret titration results by substituting data into a given mathematical formula

OCR 21st Century Science: C6 Checklist


Aiming for Grade C �� Aiming for Grade A �� understand that when dissolved in water, acids form hydrogen ions and alkalis form hydroxide ions; understand that in neutralisation reactions the hydrogen ions and hydroxide ions join together to form water

write down the formula of a salt given the formulae of the acid and alkali that react together

use and interpret energy level diagrams for exothermic and endothermic reactions

understand the importance of energy changes in managing and controlling chemical reactions such as in chemical synthesis

understand how the processes of dissolving, filtration, evaporation, crystallisation and drying are used to purify a chemical

calculate the percentage yield of a reaction given the actual and theoretical yields

describe methods for measuring rates of reactions, including measuring volumes of gases, changes in mass and the formation or loss of a colour or precipitate

interpret data obtained from rates of reaction experiments

use ideas about collisions between particles to explain how reactions take place; understand how concentration, temperature, and size of particles affect reaction rates

explain how the frequency of collisions affects the rate of reaction when concentration or particle size changes

understand the effect of catalysts on rates of reaction and that catalysts are not used up

interpret data about the control of the rate of reactions in chemical synthesis

understand the need to calculate quantities of reactants, choose suitable conditions and plan how to separate and purify products of chemical synthesis

note methods of determining the yield of a chemical synthesis and checking the purity of the product



Checklist C6 Aiming for C

Use this checklist to see what you can do now. Refer back to pages 164–189 if you’re not sure. Look across the rows to see how you could progress.

Remember you’ll need to be able to use these ideas in many ways:

� interpreting pictures, diagrams and graphs � applying ideas to new situations � explaining ethical implications � suggesting some benefits and risks to society � drawing conclusions from evidence you’ve been given.

Look at pages 300–306 for information about how you’ll be assessed.

Working towards a C grade

Aiming for Grade E �� Aiming for Grade C �� recall hazard symbols and give precautions for handling hazardous chemicals

understand the importance of chemical synthesis in providing a variety of products

identify the stages in the synthesis of a chemical compound

interpret data from various sectors of the chemical industry

recall the use of indicators to test for acidity and alkalinity

recall some solid, liquid and gaseous acidic substances and some common alkalis

recall the use of universal indicator and pH meters to measure the pH of a solution

recall the reactions of acids with metals, metal oxides, metal hydroxides and metal carbonates, and write word equations for the reactions

recall the formulae of the reactants and products of some of these reactions

interpret balanced chemical equations including state symbols

use the Periodic Table to obtain relative atomic masses and calculate the relative formula mass of compounds; understand that the relative atomic mass compares the mass of an atom with other atoms

understand that a balanced equation shows the relative number of atoms of each element in the reactants and products; substitute relative formula masses and data into a given mathematical formula to calculate the mass of a reactant or product

recall that the reaction of an acid with an alkali is a neutralisation reaction, and describe how to accurately carry out a titration

write down the name of the salt formed from a named acid and alkali in a neutralisation reaction

understand that when dissolved in water, acids form hydrogen ions and alkalis form hydroxide ions; understand that in neutralisation reactions the hydrogen ions and hydroxide ions join together to form water

OCR 21st Century Science: C6 Checklist


Aiming for Grade E �� Aiming for Grade C �� understand the terms exothermic and endothermic

use and interpret energy level diagrams for exothermic and endothermic reactions

understand the importance of the purity of chemicals and how to check this

understand the use of filtration to separate a solid from a liquid

understand how the processes of dissolving, filtration, evaporation, crystallisation and drying are used to purify a chemical

understand what is meant by rate of reaction, and understand the need to control reaction rate

describe methods for measuring rates of reactions, including measuring volumes of gases, changes in mass and the formation or loss of a colour or precipitate

use ideas about collisions between particles to explain how reactions take place; understand how concentration, temperature, and size of particles affect reaction rates

understand the effect of catalysts on rates of reaction and that catalysts are not used up

understand the need to choose reactants and a suitable reaction, and assess risk, in chemical synthesis

understand the need to calculate quantities of reactants, choose suitable conditions and plan how to separate and purify products of chemical synthesis



c6_01 Making chemicals

Resources

Student Book pages 164−165 � Homework pack c6_01

Files on Teacher Pack CD: c6_01_worksheet; c6_01_technician

Equipment for demonstrations; hazard symbols for display; video clips of industrial processes

Learning outcomes C6. 1.1 understand the importance of chemical synthesis to provide food additives, fertilisers, dyestuffs, paints,

pigments and pharmaceuticals

C6.1.2 interpret information about the sectors, scale and importance of chemical synthesis in industry and in

laboratories

C6.1.6 recall the main hazard symbols and be able to give the safety precautions for handling hazardous

chemicals (limited to explosive, harmful, toxic, corrosive, oxidizing, and highly flammable)

C6.2.1 identify the stages in a given chemical synthesis of an inorganic compound (limited to acid–alkali

reactions), including: a. choosing the reaction or series of reactions to make the required product, b. carrying out a

risk assessment, c. working out the quantities of reactants to use, d. carrying out the reaction in suitable

apparatus in the right conditions (such as temperature, concentration), e. separating the product from the reaction

mixture (limited to filtration), f. purifying the product (limited to evaporation, crystallisation and drying in an oven or

desiccator), g. measuring the yield and checking the purity of the product (by titration)

Literacy focus: Describing hazards and using flow charts.

Numeracy focus: Plotting, drawing and interpreting graphs and charts from secondary data.

ICT focus: Viewing video clips to illustrate the manufacture of chemicals on a large scale in industry.

In this lesson students are learning to:

� recall hazard symbols and safety precautions for dealing with hazardous chemicals

� use information about how chemical synthesis is used in the chemical industry

� name the stages in the development of the synthesis of a new chemical

Key vocabulary

chemical synthesis


Data on the chemical industry given in websites can be difficult for students to understand and interpret. Examples

need to be chosen carefully. One to try is the website of the European Chemicals Agency (ECHA).

Stimuli and starter suggestions

� ‘What has the chemical industry done for us?’ Give students this question and ask them to discuss and list the

benefits of the chemical industry. Answers may include useful products (drugs, plastics, paints), jobs, money

from sale of exports.

Learning activities worksheet c6_01 Low demand � Ask students to list the hazardous chemicals they may find in their homes. The list should include

fuels and foods (flour, sugar, oils) – flammable; cleaning materials – toxic, corrosive; drugs – toxic. Students may

not see foods as being a hazard but you could demonstrate the flammability of some common foodstuffs

(technician sheet). Ask students to consider what should be done to reduce the risk from these substances

(particularly the toxic, corrosive products). Guide students to including hazard symbols (display those that they

need to know), secure (childproof) packaging. Students may not have come across the oxidising hazard symbol

before. This can be demonstrated by the ‘screaming jelly baby’ experiment (technician sheet). Show some

examples of cleaning materials with these precautions. Discuss how hazardous chemicals should be handled

(Student Book p. 164 gives a list of precautions). Activity 1 on the worksheet provides further tasks on this theme.

Teaching and learning notes: Students should recall hazard symbols from previous lessons but they need

reinforcing here, along with safe handling of chemicals.

Standard demand � Discuss the range of manufactured chemical products that we use including processed foods,

cleaning products, cosmetics and drugs. Introduce the term ‘synthesis’ to begin the discussion of how these

products are manufactured. Ask groups of students to list the stages in the process before referring to the Student

c6_01 Making chemicals continued


Book for the flowchart on p. 165. Show video clips of industrial processes and ask the students to consider how the

stages in the flow chart match the processes shown. Give out recipes from a cookery book and ask students to

identify the similarities and differences between these and the stages in a chemical synthesis. There are more

tasks in Activity 2 on the worksheet.

Teaching and learning notes: The stages in a chemical synthesis are introduced here but each step in the

process will be examined in more detail in later lessons. By the end of the module, students should recall the steps

and understand what happens in each. Note that stage 3 of the flowchart on p. 165 is largely a Higher tier task.

High demand � Having looked at the stages in chemical synthesis and at reducing the risk from hazardous

chemicals, try to give students a sense of the scale of the chemical industry in the UK and worldwide – there is no

part of their lives which is untouched by it. The pie chart on Student Book p. 165 gives the various sectors of the

chemical industry. Students could investigate companies in these sectors on the internet and report on their

products and importance. Activity 3 on the worksheet provides further activities on this.

Plenary suggestions Play ‘plus’/’minus’/’want to know more’ – choose the name of a company using chemical processes (that may be

setting up a factory) in your area. Ask students to suggest a ‘plus’ (new products, jobs) , a ‘minus ‘(hazards,

pollution) and a question they might want to ask. Examples of companies – Proctor & Gamble (cleaning materials),

Astra-Zeneca (drugs), ICI (Dulux paints), Heinz (processed food).

Student Book answers Q1 Explosive; toxic

Q2 Check the hazard symbol; wear gloves and goggles; make sure it cannot fall over/spill; make sure no one is

likely to touch it when it is thrown away; choose something that is less hazardous.

Q3 1, 2, 3, 4 and 5

Q4 Nitrogen and hydrogen are combined to make a new substance.

Q5 The synthesis of new substances produces products that can be sold for more than the raw materials; e.g.

(from the pie chart) drugs, polymers, etc.

Q6 Basic chemicals are used to synthesise drugs (and other products); which have a higher value.

Worksheet answers Activity 1 (Low demand)

Q1 The label should include hazard signs for ‘harmful’ and ‘oxidising agent’; warnings and instructions for handling

the product; the container should have a secure top.

Q2 a) F; b) C, E; c) D; d) A; e) B

Q3 Wear goggles, gloves and overalls; check the labels on spilled bottles; clear up spilled materials, but do not let

them go down the drain.

Activity 2 (Standard demand)

Q1 A and D; both involve small molecules combining to form larger molecules (or similar).

Q2 a) See ingredients list.

b) Heating the mixture; make sure the temperature doesn’t rise too high.

c) See ingredients list.

d) High temperature (60 °C) for mixing; low temperature (5 °C and −20 °C) for freezing the mixture.

e) Scooped out of the ice cream maker

f) Make sure the saucepan, bowl and stirring spoon are clean.

g) Put the ice cream in a measuring jug; or weigh it. Taste it!

Q3 Answers should include a range of chemicals.

Activity 3 (High demand)

Q1 a) Pharmaceuticals and basic; b) Paint, pigments and dyes; (c) 5%; d) £12 billion

Q2 a) Accurate bar chart; or scatter graph with points joined (not best fit)

b) 18 million tonnes increase; c) It continued to increase.

d) Production may have been less owing to a shortage of raw materials; or a lower demand for sulfuric acid.




Technician sheet

Equipment and materials

� bench mat

� tripod, gauze, pipe-clay triangle

� Bunsen burner

� crucible and lid

� splints

� spatula

� flammable foods – flour, bread, sugar, cooking oil, whisky/gin/brandy

� bottles of cleaning fluids

� drain cleaner

� oven cleaner

� weedkiller – preferably with warning symbols and safety tops

� drug bottles

� jelly babies

� Pyrex boiling tube

� clamp stand

� Bunsen burner

� potassium chlorate(V)

Method

1 Flammable solids can be put on a bench mat or on a gauze on a tripod and ignited with a lighted splint or Bunsen flame.

A few cm3 of the flammable liquids can be put in a crucible and ignited with a lighted splint. Cooking oils will need to be heated before they can be ignited.

Flames can be put out by smothering with a bench mat.

2 Hand around the bottles of cleaning fluids for students to examine the labels and the tops.

3 ‘Screaming jelly baby’ demonstration. See the Health and Safety notes below. Place two spatulas (no more than 15 g) of potassium chlorate(V) in the tube. Clamp the boiling tube at a slight angle to the vertical. Heat the tube until the potassium chlorate(V) melts. Using tongs, drop one jelly baby into the boiling tube.

Health and Safety notes

� Use safety screens to keep students away from the demonstration of flammable materials. Wear goggles.

� Bottles of cleaning fluids should be empty and washed before they are handled by students.

� The ‘screaming jelly baby’ demonstration should be carried out in a fume cupboard. This experiment has a considerable risk. Check that your school Health and Safety policy will allow it to be demonstrated. Potassium chlorate(V) is HARMFUL as well as being an OXIDISING agent. Wear a face shield and heat-resistant gloves. There will be clouds of smoke as well as a ‘screaming’ noise. It is an exciting experiment and can lead to a great deal of discussion of the combustion of foodstuffs, and the role of oxidising agents/accelerants – for example in rockets.




1 Safety with chemicals

1 ‘Kleeneezy Ltd’ have asked you to design the packaging for a new cleaning product they have developed. The product is used for cleaning toilets, baths and washbasins. It is a harmful (irritant) liquid and can act as an accelerant in fires. Design the packaging and the label for the product, and write a letter to Kleeneezy describing the safety features of your design.

2 Which of the hazard symbols shown below should be put on each of the products listed? Some of the products may need more than one symbol.

a) A liquid fuel used to start off a barbecue ..........

b) A weedkiller that is poisonous and can make fires burn faster ..............

c) A solid that ‘eats away’ the hair and fats that block drains ............

d) Fireworks ............

e) A solid added to washing machines (to stop scum forming) irritates the skin ..........

3 Thieves have broken into a storeroom containing hazardous chemicals at a chemical factory. They have smashed and spilled some of the dangerous substances. You are part of the special team sent into clean up the mess. How would you do the job as safely as possible?

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2 Developing new products

1 Which of the following chemical processes are examples of synthesis? Explain your answer.

A Combining sulfur, oxygen and water to make sulfuric acid

B Separating the substances in crude oil for use as fuels in various vehicles

C Breaking down limestone in a furnace to produce lime for the cement industry

D Joining together small ethene molecules to make the polymer, polyethene

2 Look at this recipe for making ice cream.

Let’s treat this recipe as a chemical process.

a) What are the reactants?

b) Are there any hazards in the process? What should you do to reduce the risk?

c) What amounts of the reactants are needed?

d) What conditions are required to make the ice cream?

e) How is the product collected?

f) How do you stop impurities entering the ice cream?

g) How do you find out how much ice cream you’ve made? How can you test it?

3 Think about all the substances that you use every day. Make a list of substances that have been manufactured by the chemical industry. (If possible look at the ingredients list of food packets, cleaners, shampoos, cosmetics, etc.)

Vanilla ice cream

Ingredients: 1 cup white sugar, 1 cup milk, 2 cups cream, 2 eggs, 1 tablespoon lemon juice, 1½ teaspoons vanilla flavouring

Directions: Mix the sugar, eggs and milk in a saucepan and heat gently (60 °C) for 10–15 minutes, stirring continuously until the mixture thickens. Allow it to cool.

Add the lemon juice and vanilla to the cream and whip it in a bowl until it is stiff. Add it to the saucepan.

Cool the mixture in a refrigerator (5 °C) for 8 hours, and then freeze it in an ice cream maker (−20 °C).



3 The chemical industry

1 Look at the pie chart showing the value of sales in sectors of the British chemical industry and then answer the questions.

a) Which two sectors together account for over half of the total sales of chemical in the UK?

b) Which single sector makes up one-tenth of the sales of the British chemical industry?

c) What is the percentage of sales of the sector that includes lipsticks and deodorants?

d) If the total sales of the chemical industry were £40 billion, what was the value of sales of drugs?

2 China has become the biggest producer of chemicals in the world. The synthesis of sulfuric acid is an important in many sectors of industry. The data below shows the production of sulfuric acid in China over a six-year period.

a) Plot a graph, or chart, of the production of sulfuric acid in China from 2000 to 2005.

b) What was the change in production between 2001 and 2005?

c) What does the data suggest happened to production of sulfuric acid in China after 2005?

3 What factors could alter the pattern shown by your graph?

Year 2000 2001 2002 2003 2004 2005

Sulfuric acid production (million tonnes)

24 28 31 34 40 46



c6_02 Acids and alkalis

Resources

Student Book pages 166−167 � Interactive Book: Practical investigations ‘The pH meter’ � Homework pack c6_02

Files on Teacher Pack CD: c6_02_practical; c6_02_technician

Equipment for class practicals and demonstrations

Learning outcomes C6.1.7 recall examples of pure acidic compounds that are solids (citric and tartaric acids), liquids (sulfuric, nitric

and ethanoic acids) or gases (hydrogen chloride)

C6.1.8 recall that common alkalis include the hydroxides of sodium, potassium and calcium

C6.1.9 recall the pH scale

C6.1.10 recall the use of litmus paper, universal indicator and pH meters to detect acidity and alkalinity, and the

use of universal indicator and pH meters to measure pH

Literacy focus: Reporting observations and learning names of acids and alkalis.

ICT focus: Using dataloggers to record pH measurements.


� recall how to test a substance to find out if it is an acid or an alkali

� recall the names of some acids and alkalis

� describe how to measure the pH of acids and alkalis and what the pH number means

Key vocabulary

indicator �� acid �� alkali �� pH scale


Recalling a long list of names can be difficult unless they are related to observations or other facts about materials.


� Explain that acids and alkalis are important reactants and products in the chemical industry. Ask students to

match some common acids and alkalis with their uses – e.g. sulfuric acid for car batteries; nitric acid for fertilisers

and explosives; ethanoic acid in vinegar; phosphoric acid in cola drinks; sodium hydroxide as drain cleaner;

ammonia as disinfectant; calcium in mortar and cement.

Learning activities practical c6_02 Low demand � Students should carry out the first experiment (P1) on the practical sheet in which they use litmus

and universal indicator to test various solutions and decide which are acids and which are alkalis. As a group or

class activity, ask students to classify named substances (written on cards or using a interactive whiteboard) as

acids or alkalis.

Teaching and learning notes: Students need to learn the names of some common acids and alkalis along with

methods of testing for acidic and alkaline properties.

Standard demand � If the students need reminding about tests for acids and alkalis then they can carry out the

first experiment (P1) on the practical sheet. An extension to this activity is to use other indicators. Then ask them to

consider what substances are acids (and alkalis). The practical sheet suggests a second experiment (P2) in which

students test dry/pure and moist/solution of solid, liquid and gaseous acids with universal indicator (note that some

of these tests must be demonstrated to students) to show that water is needed to make a substance act as an acid.

Use a matching exercise to test recall of solid, liquid and gaseous acids and alkalis.

Teaching and learning notes: Students will need to learn to recognise the names of a variety of acids and alkalis.

High demand � Higher-attaining students should investigate the pH scale further by carrying out experiment P3 on

the practical sheet. They test a variety of solutions with universal indicator and with a pH meter. They should record

a range of pH values, but discussion of strong and weak acids and alkalis is not necessary at this stage. Assess

the students’ ability to assign the terms acid or alkaline correctly to the ranges of pH numbers. Make sure that

students understand how to use a pH meter even if there are insufficient available to be used by a whole class (see

technician sheet). Test knowledge of the pH scale.

c6_02 Acids and alkalis continued


Plenary suggestions This lesson is largely about recall, so ask the students to write out a list of names of acids and alkalis, correctly

categorised, with a ‘prize’ for the longest and most accurate list.

Student Book answers Q1 It is an alkali/is alkaline.

Q2 Add litmus solution/paper to it; check that it goes red.

Q3 a) Ethanoic acid; b) citric acid/ tartaric acid (or other)

c) sodium/ potassium/calcium hydroxide; d) sulfuric/nitric acid

Q4 a) To calibrate it/check that it is reading accurately.

b) To remove any other acid or alkali.

Q5 An solution can have a lower pH than 1; or higher than 14.

Practical sheet answers Experiment P1 (Low demand)

Q1 a) red; b) red (to orange)

Q2 a) blue; b) (blue to) violet

Q3 Indicators

Q4 It is an alkali.

Q5 It is acidic.

Q6 Test a sample of the solution with litmus paper/solution or universal indicator paper/solution; if it turns blue the

sample is an alkali.

Experiment P2 (Standard demand)

Q1 An acid makes an indicator turn a particular colour; e.g. litmus is red in acids.

Q2 Only when dissolved in water.

Experiment P3 (High demand)

Q1 Sulfuric, hydrochloric, nitric acid, ethanoic acid, citric acid, distilled water, ammonia, calcium hydroxide, sodium

hydroxide

Q2 Disagreement may be caused by misreading the colour chart, poor calibration and washing of the pH electrode,

insufficient stirring of the sample solution or not waiting for the pH reading to stabilise.

Q3 The pH meter must be checked against a solution of known pH to ensure that it is giving the correct reading; it

must be washed to avoid contaminating the test samples, hence giving an inaccurate measurement.



c6_02 Acids and alkalis

P1 Recognising acids and alkalis

Objectives

In this activity you will:

� learn how to identify solutions as acids or alkalis.

The acid and alkali solutions can irritate the skin and can damage eyes. Wear goggles and a lab coat and avoid spillages.


test tubes • test tube rack • droppers • litmus solution or paper • universal indicator solution or paper

• access to solutions of: sulfuric acid, hydrochloric acid, ethanoic acid, sodium hydroxide solution,

limewater, ammonia solution

Method

1 Put a dropper-full of one of the test solutions into two clean test tubes.

2 Add one or two drops of litmus solution to one test tube or drop a piece of litmus paper into the test tube. Shake the test tube gently.

3 Add one or two drops of universal indicator to the other test tubes, or drop a piece of universal indicator paper into the tube.

4 Put the test tubes into the test tube rack. Record the name of the test solution and the colour of the litmus and the universal indicator.

5 Wash out the test tubes thoroughly.

6 Repeat the test with another test solution. Make sure you wash out your test tubes carefully and use a clean dropper.

Results

Make a table based on this one. Complete your results table for all the test solutions.

Name of test solution Colour of litmus Colour of universal indicator

Questions

1 What is the colour in acids of: a) litmus, b) universal indicator?

2 What is the colour in alkalis of: a) litmus, b) universal indicator?

3 What is the name given to substances that behave in the same way as litmus?

4 A solution of potassium hydroxide turns litmus blue. What does this tell you about potassium hydroxide?

5 A sample of lemonade turns universal indicator orange. What does this tell you about lemonade?

6 Describe how you could show that a liquid is an alkali.



P2 What substances are acids?

Objectives


� learn the names of some solids, liquids and gases that are acidic

� substances are only acidic when in solution. Acids and alkalis can irritate the skin and can damage eyes. Wear goggles and avoid spillages.


test tubes • test tube rack • droppers • watch glass • spatula • universal indicator paper

• access to: citric acid, tartaric acid, dilute sulfuric acid, dilute nitric acid, dilute ethanoic acid

Method

1 Put a little solid citric acid on to a watch glass. Touch the acid with a piece of dry universal indicator paper. Record what you see.

2 Now wet a piece of universal indicator paper and again touch it to the solid acid. Record what you see.

3 Repeat steps 1 and 2 with solid tartaric acid.

4 Pour about 2 cm3 each of dilute sulfuric acid, nitric acid and ethanoic acid into separate test tubes. Dip a piece of universal indicator paper in each and record your observations.

5 Your teacher may show you what happens when universal indicator paper is put into pure sulfuric acid and pure ethanoic acid. Record what you see.

6 Your teacher may show you what happens when dry and moist universal indicator paper is put in hydrogen chloride gas. Record what you see.

Results

Write down your observations in a suitable table.

Questions

1 How can you tell if a substance is an acid?

2 When do acidic substances act as acids?



P3 Measuring pH

Objectives


� learn how to measure the pH of acids and alkalis.

Acids and alkalis can irritate the skin and can damage eyes. Wear goggles and a lab coat and avoid spillages.


small beakers • universal indicator paper • pH meters • distilled water

• access to solutions of: sulfuric acid, nitric acid, ethanoic acid, citric acid,

sodium hydroxide, calcium hydroxide, ammonia

Method

1 Collect a sample of one of the acids or alkali in a small beaker.

2 Dip a piece of universal indicator into the solution, take the paper out of the solution, and match the colour against the colours on a pH chart.

3 Place the electrode end of the pH meter in the solution. Stir it around gently for a few seconds – when the reading has stopped changing, record the pH value. Take the pH electrode out of the solution and wash it in distilled water.

4 Wash out your beaker and repeat the measurements with a different sample.

Results

Write down your measurements in a suitable table.

Questions

1 Write the names of your samples in order of pH – from the lowest to the highest – and mark which are acids and which are alkalis.

2 Do your results with the universal indicator paper agree with the measurements using a pH meter? Suggest reasons why they may not agree.

3 Why is it important to calibrate a pH meter and wash the electrode after each measurement?



c6_03 Reactions of acids

Resources

Student Book pages 168−169 � Interactive Book: Drag and drop ‘Acid–base reactions’; Naked Scientist animation ‘How do we balance chemical equations?’; Practical investigations ‘How to use chemical equations’ � Homework pack c6_03

Files on Teacher Pack CD: c6_03_practical; c6_03_worksheet; c6_03_technician

Packet of Epsom salts; equipment for class practical

Learning outcomes C6.1.11 recall the characteristic reactions of acids that produce salts, to include the reactions with metals and their

oxides, hydroxides and carbonates

C6.2.1 identify the stages in a given chemical synthesis of an inorganic compound (limited to acid-alkali

reactions), including: a. choosing the reaction or series of reactions to make the required product

In this and subsequent lessons:

C6.1.3 recall the formulae of the following chemicals: chlorine gas, hydrogen gas, nitrogen gas, oxygen gas,

hydrochloric acid, nitric acid, sulfuric acid, sodium hydroxide, sodium chloride, sodium carbonate, sodium nitrate,

sodium sulfate, potassium chloride, magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium

chloride, magnesium sulfate, calcium carbonate, calcium chloride and calcium sulfate

C6.1.4 work out the formulae of ionic compounds given the charges on the ions

C6.1.5 work out the charge on one ion given the formula of a salt and the charge on the other ion

C6.1.12 write word equations when given appropriate information

C6.1.13 interpret symbol equations, including the number of atoms of each element, the number of molecules of

each element or covalent compound and the number of ‘formulas’ of ionic compounds, in reactants and products

In this context, ‘formula’ is used in the case of ionic compounds as an equivalent to ‘molecules’ in covalent

compounds; the concept of the mole is not covered in the specification

C6.1.16 recall the state symbols (s), (l), (g) and (aq) and understand their use in equations

C6.1.14 balance unbalanced symbol equations

C6.1.15 write balanced equations including state symbols (s), (l), (g) and (aq) to describe the characteristic

reactions of acids and other reactions when given appropriate information

Numeracy focus: Using ideas of ratios in the context of formulae of ionic compounds; balancing equations.


� recall patterns in the reactions of acids

� interpret chemical equations for the reactions of acids

� write chemical equations for the reactions of acids

Key vocabulary

salt


The number of possible combinations of acids and salts make it difficult for some students to recall all the formulas

required by the specification.


� Show a packet of Epsom salts (or display pictures of packets) and a list of what it can be used for – bath salts,

face scrub, removing splinters, hairspray remover, etc. Tell students that the chemical industry recognises that

there is a demand for Epsom salts (magnesium sulfate) and wants ideas for how it can be manufactured (react

sulfuric acid with magnesium, magnesium oxide, magnesium hydroxide or magnesium carbonate).

Learning activities worksheet c6_03 + practical c6_03 Low demand � Assess students’ response to the starter activity and judge how much reinforcement of this topic is

required. Introduce the practical sheet, which reacquaints students with the reactions of acids visually. On this

occasion there is insufficient time to prepare crystals of the salts but make sure that students understand that the

products of all the reactions are salts. Explain the word equations for examples of the reactions. Show samples of

some salts to emphasise they are a class of compounds – not just one – i.e. with different properties but all formed

from an acid and containing a metal. The worksheet provides more opportunities for students to test understanding.

Teaching and learning notes: This lesson revises students’ knowledge of the reactions of acids and reinforces

their recall of the patterns of reactions as expressed in word equations.

c6_03 Reactions of acids continued


Standard demand � Students can carry out the practical activity in the low demand section. Display examples of

equations for reactions of acids (such as those in the Student Book p. 168) noting the patterns in the reactions and

pointing out the formulas of the salts. Explain that with this knowledge they, like the chemical industry, can decide

which reactants to use to make a particular salt. There are further tasks on this in the worksheet.

Teaching and learning notes: Students will need to recall the formulae of certain salts. Understanding and

interpreting equations will also be covered in lessons that follow.

High demand � (Higher tier only) Extend the activities described above to writing formulae and equations for the

reactions of acids. The worksheet gives more examples. For students unfamiliar with writing the formulae of salts,

(see Student Book C4 p. 125) explain that salts are ionic compounds made up of positively charged metal ions and

negatively charged ions derived from an acid. Explain how the charges must balance, and hence how the formula

is written. For students who have not previously written balanced equations, explain the procedure as described

briefly in the Student Book. For more detail refer to Student Book C4 p.115 and C5 p.169.

Plenary suggestions Flash up formulas of salts and ask students to name them along with reactants that could be used to produce

them. (Learning outcome C6.1.3 gives the list of formulae that students should recognise.)

Student Book answers Q1 a) Magnesium chloride, hydrogen; b) potassium sulfate, water; c) magnesium chloride, water

d) calcium nitrate, water, carbon dioxide

Q2 a) Sodium sulfate, sulfuric acid; b) magnesium chloride, hydrochloric acid; c) potassium nitrate, nitric acid

Q3 Calcium hydroxide solution reacts with hydrochloric acid solution to make calcium chloride solution and (liquid)

water.

Q4 CuCl2, ZnSO4, Fe(NO3)3 Q5 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)

Q6 K2CO3(s) + 2HCl(aq) → 2KCl(aq) + H2O(l) + CO2(g)


Q1 Calcium, sulfuric acid with calcium sulfate ; magnesium oxide, nitric acid with magnesium nitrate; potassium

hydroxide, hydrochloric acid with potassium chloride; sodium carbonate, sulfuric acid with sodium sulfate

Q2 a) Magnesium + sulfuric acid → magnesium sulfate + hydrogen; b) Calcium oxide + nitric acid → calcium nitrate

+ water; c) Sodium hydroxide + hydrochloric acid → sodium chloride + water

d) Potassium carbonate + nitric acid → potassium nitrate + water + carbon dioxide

Q3 Nitric acid + calcium/calcium oxide/calcium hydroxide/calcium carbonate; correct word equation


Q1 a) Sodium chloride; b) magnesium sulfate; c) calcium chloride; d) sodium nitrate; e) potassium chloride;

f) calcium sulfate

Q2 a) (i) Calcium, nitric acid – calcium nitrate; (ii) Potassium hydroxide, sulfuric acid – potassium sulfate

(iii) magnesium oxide, hydrochloric acid – magnesium chloride; (iv) sodium carbonate, nitric acid – sodium

nitrate

b) i and iv; fizzing/gas evolved; c) ii only

Q3 Sulfuric acid + zinc/zinc oxide/zinc hydroxide/zinc carbonate; correct word equation


Q1 a) K2SO4; b) ZnCl2; (c) Al(NO3)3; d) MgSO4; e) FeCl2

Q2 a) Mg(s) + 2HNO3(aq) → Mg(NO3)2(aq) + H2(g); b) Ca(OH)2(s) + 2HCl(aq) → CaCl2(aq) + H2O(l)

c) CuO(s) + H2SO4(aq) → Cu SO4(aq) + H2O(l); d) FeCO3(s) + H2SO4(aq) → FeSO4(aq) + H2O(l) + CO2(g)

Q3 Corresponding balanced equations for the reactants suggested.

Practical sheet answers Q1 Test 1: acid + metal → salt + hydrogen gas; Test 2: acid + metal oxide → salt + water

Test 3: acid + metals carbonate → salt + water + carbon dioxide gas

Q2 Test 1: zinc chloride; Test 2: iron(III) sulfate; Test 3: copper sulfate

Q3 Test 1: zinc + hydrochloric acid → zinc chloride + hydrogen;

Test 2: iron(III) oxide + sulfuric acid → iron(III) sulfate + water

Test 3: copper carbonate + sulfuric acid → copper sulfate + water + carbon dioxide

Q4 Test 1: Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g); Test 2: Fe2O3(s) + 3H2SO4(aq) → Fe2(SO4)3(aq) + 3H2O(l)

Test 3: CuCO3(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) + CO2(g)

(‘III’ is not needed in Q2 and Q3

for Foundation tier students)



c6_03 Investigating reactions of acids

P Patterns in the reactions of acids

Objectives


� revise your knowledge of the reactions of acids and the preparation of salts.

Acids are CORROSIVE. Wear goggles and a lab coat. Wipe up all spillages immediately with a wet cloth.


• test tubes • boiling tube • test tube rack • Bunsen burner • tongs • spatula • stirring rod • splints

• right-angled delivery tube with bung to fit test tube • access to: dilute hydrochloric acid, dilute sulfuric

acid, zinc granules, iron(III) oxide, copper carbonate, limewater

Method

Test 1: Half-fill a test tube with dilute hydrochloric acid. Add one or two pieces of zinc. Collect the gas given off by holding another test tube upside down over the first. Test the gas with a lighted splint.

Test 2: Pour dilute sulfuric acid into a boiling tube to a depth of 2–3 cm. Using tongs, hold the boiling tube in a Bunsen flame for a few seconds until it is warm. Take the boiling tube out of the flame and add a little iron(III) oxide using a spatula. Stir the mixture. If all the solid dissolves, add a little more.

Test 3: One-third fill a test tube with dilute sulfuric acid. Add a little copper carbonate on the end of a spatula. Fit a delivery tube quickly and bubble the gas through some limewater in another test tube.

Results

Record all your observations and identify the gases given off.

Questions

1 Complete the patterns of the reactions:

Test 1: acid + metal →

Test 2: acid + metal oxide →

Test 3: acid + metal carbonate →

2 Name the salt formed in each of the reactions.

3 Write a word equation for each of the reactions.

Extension (Higher tier only)

4 Write balanced equations for the reactions.



c6_03 Reaction of acids

Technician sheet


Demonstration:

Packet of Epsom salts

Practical:

Each group of students will need:

� test tubes

� boiling tube

� test tube rack

� Bunsen burner

� tongs

� spatula

� stirring rod

� splints

� right-angled delivery tube with bung to fit test tube

Access to:

� dilute hydrochloric acid (1 mol dm−3)

� dilute sulfuric acid (1 mol dm−3)

� zinc granules, iron(III) oxide, copper carbonate, limewater

� Samples of salts: e.g. sodium chloride, magnesium sulfate, cobalt chloride, zinc nitrate

Method

Full instructions are given on practical sheet c6_03.

Notes

� Students may need assistance in testing for hydrogen and carbon dioxide.

� The reaction between zinc and hydrochloric acid is slow at the beginning. A little warming may help.

� Students should make the following observations:

Test 1: fizzing, gas burns with an explosive ‘pop’ – they may notice the zinc pieces breaking up but will probably not see them dissolving

Test 2: an orange-red solution is formed; no gas evolved

Test 3: fizzing, gas turns limewater cloudy, a blue solution is formed.

Health and Safety:

� The hydrochloric and sulfuric acids used are CORROSIVE. Copper carbonate is HARMFUL, so avoid inhaling the powder. Goggles and a lab coat must be worn and any spillages cleared up immediately.



c6_03 Reactions of acids

1 Reaction patterns

1 Draw lines to match the names of the salts formed with the reactants that form them:

Reactants Salts

calcium, sulfuric acid potassium chloride

magnesium oxide, nitric acid sodium sulfate

potassium hydroxide, hydrochloric acid calcium sulfate

sodium carbonate, sulfuric acid magnesium nitrate

2 Complete the word equations for the following reactions:

a) magnesium + sulfuric acid → ..................................................................................

b) calcium oxide + nitric acid → ...................................................................................

c) sodium hydroxide + hydrochloric acid → .................................................................

d) potassium carbonate + nitric acid → .......................................................................

3 ‘Growplant’ is a company that makes fertilisers for farmers and gardeners. They want to produce calcium nitrate. Write a letter to the company suggesting the reactants and the reaction that could be used to manufacture calcium nitrate. Include a word equation in your answer.

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c6_03 Reactions of acids continued


2 Names and equations

1 What are the names of the salts that have the formulae shown below?

a) NaCl b) MgSO4 c) CaCl2 d) NaNO3 e) KCl f) CaSO4

2 a) Look at the equations shown below. Name the reactants and the salt formed in each reaction.

i) Ca(s) + 2HNO3(aq) → Ca(NO3)2(aq) + H2(g)

ii) 2KOH(aq) + H2SO4(aq) → K2SO4(aq) + H2O(l)

iii) MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)

iv) Na2CO3(s) + 2HNO3(aq) → 2NaCl(aq) + H2O(l) + CO2(g)

b) In which reactions will it be obvious that a reaction is taking place? Explain your answer.

c) In which reactions are both reactants in solution?

3 ‘Healthy Life’ is a company that manufactures food supplements. Zinc is an essential mineral in the diet and Healthy Life wants to manufacture pure zinc sulfate for sale to the public. Write a brief report describing the reactants and process that you could use to make zinc sulfate. Include a word equation in your report.

3 Formulae and equations (Higher tier only)

1 Use the tables above to write the formulae of the following salts:

a) potassium sulfate b) zinc chloride c) aluminium nitrate

d) magnesium sulfate e) iron(II) chloride.

2 Use the following descriptions of reactions to write balanced chemical equations, including state symbols. Use the tables above to help you.

a) When pieces of magnesium (Mg) are put in dilute nitric acid solution, there is fizzing and a gas is given off that pops when lit.

b) Calcium hydroxide powder (Ca(OH)2) appears to dissolve when put in dilute hydrochloric acid solution.

c) Solid copper oxide (CuO) dissolves in sulfuric acid solution to form a blue solution.

d) Iron(II) carbonate (FeCO3) powder effervesces when put in dilute sulfuric acid, forming a pale green solution. The gas turns limewater cloudy.

3 Answer question 3 in activity 1 and question 3 in activity 2 above, including balanced chemical equations in your answers.



c6_04 Reacting amounts

Resources


Files on Teacher Pack CD: c6_04_worksheet; c6_04_practical; c6_04_technician

Equipment for class practical

Learning outcomes C6. 2.4 understand that a balanced equation for a chemical reaction shows the relative numbers of atoms and

molecules of reactants and products taking part in the reaction

C6.2.5 understand that the relative atomic mass of an element shows the mass of its atom relative to the mass of

other atoms

C6.2.6 use the Periodic Table to obtain the relative atomic masses of elements

C6.2.7 calculate the relative formula mass of a compound using the formula and the relative atomic masses of the

atoms it contains

C6.2.8 substitute relative formula masses and data into a given mathematical formula to calculate reacting

masses and/or products from a chemical reaction

C6.2.9 calculate the masses of reactants and products from balanced equations


reactions), including: c. working out the quantities of reactants to use

Ideas about Science IaS 1.1 data are crucial to science. The search for explanations starts from data; and data are collected to test

proposed explanations

IaS 1.2 we can never be sure that a measurement tells us the true value of the quantity being measured

IaS 1.3 if we make several measurements of any quantity, these are likely to vary

Numeracy focus: Carrying out calculations using experimental data; calculating reacting masses.

ICT focus: Logging and storing data, and displaying data in a variety of formats for analysis.


� calculate relative formula masses using the Periodic Table

� calculate the mass of reactants and products in a chemical reaction

Key vocabulary

formula �� relative formula mass


Some students will have difficulty handling the ratios of reacting quantities.


� Display a recipe for a meal and ask students to suggest reasons why the quantities of ingredients are listed.

Learning activities worksheet C6_04 + practical c6_04 Low demand � Ask students to explain the term ‘relative atomic mass’ (RAM) and how it can be found (in a

Periodic Table). Give students the formula of a compound such as magnesium oxide, MgO, and ask them if they

recall the term ‘relative formula mass’ (RFM) and how it is calculated for molecules and ‘formula units’ of ionic

compounds. Explain things to those unfamiliar with the idea (Student Book p. 170). The worksheet gives further

examples for students to try. Students should carry out the experiment on the practical sheet and answer questions

1–3. Note that they need to keep their samples and data for a later lesson.

Teaching and learning notes: Students may have met RFM in a previous lesson (see Student Book C5 p.150).

Standard demand � Discuss the term ‘relative formula mass’ and the data contained in an equation – such as that

for magnesium reacting with hydrochloric acid (Student Book p. 170) – the number of molecules/formula units and

the reacting amounts, given by expressing the RFMs in grams. Use a spreadsheet format to calculate the amounts

of products given different amounts of reactants; or products using the ratios of reactants and products. Students

can use IT to generate a spreadsheet that does the calculations for them. Alternatively give them a formula to use

such as given in the worksheet and practical sheet. Students should carry out the experiment on the practical sheet

c6_04 Reacting amounts continued


and answer questions 1–4. Ask them to discuss how certain they are of the data they have recorded and

calculated. How could they be sure that their weighings are the true values? (Use repeat measurements.) How

certain are they that the mass of copper carbonate calculated to have reacted has actually done so? Discuss the

sources of errors and the uncertainty in data.

Teaching and learning notes: Students will need to recognise that the mass ratio from the chemical equation is

the same for all given amounts of a reactant or product. Note that students need to keep their samples and data for

a later lesson.

High demand � (Higher tier only) After the practical work, Higher tier students should answer all the questions,

including the extension questions. Point out that industrial chemical engineers must calculate carefully how much

reactants are required to make a certain amount of a product because using too little or too much could have

serious financial consequences. Ask students to try the questions in activity 3 on the worksheet, where they have

to use an equation to work out the formula for calculating reacting masses.

Plenary suggestions Ask students what data are needed to plan the manufacture of 1 tonne of Epsom salts (magnesium sulfate) –

which reactants, what equation? Then ask them to work out the amounts of reagents needed. For Foundation tier

students give the formula.

Student Book answers Q1 111

Q2 85

Q3 190 g

Q4 a) Nitric acid; 1; 85; 85 g; b) 8.5 g

Q5 a) 30 tonnes; b) 80 tonnes; c) Magnesium; smallest formula mass/no atoms of other elements


Q1 a) 39; b) 32; c) 65; d) 80; e) 207

Q2 Manganese atoms have a mass of 55 compared to carbon, which has a mass of 12 on the same scale.

Q3 a) 44; b) 63; c) 17

Q4 a) 95; b) 187.5; c) 174


Q1 a) 2; b) 1

c) (i) 18 g; (ii) 36 g; (iii) 1.8 g

Q2 a) BaCO3; b) (i) 197; (ii) 208; c) 473.6 kg

d) There is always variation in measurements because of errors – e.g. some of the reactants may not have

reacted; some of the product may have been lost.


Q1 a) 3.15 g; b) 5.05 g

c) Errors in measurements; reaction not complete/reactants not used up; some of the product lost.

Q2 a) Ag2O(s) + H2SO4(aq) → Ag2SO4(aq) + H2O(l); b) 223.1 kg

Practical worksheet answers Q1 The fizzing stopped; no more carbon dioxide was evolved.

Q2 Check student’s result.

Q3 a) 123.5; b) 159.5

Q4 1.3 × answer to Q2

Q5 a) CuCO3(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) + CO2(g)

b) 0.247 g




P Making a salt

Objectives


� find the mass of reactants required to make a salt.

Sulfuric acid is CORROSIVE; wear goggles and a lab coat. Copper carbonate is HARMFUL; avoid inhaling the powder. Copper sulfate is TOXIC. Report all spillages to your teacher.


measuring cylinder • small beaker • crystallising dish • spatula • stirring rod

• copper carbonate • sulfuric acid • access to a balance

Method

1 Measure out 20 cm3 of sulfuric acid. Pour the acid into a small beaker.

2 Weigh about 0.5 g of copper carbonate powder accurately. Record the mass.

3 Using a spatula, add a little of your copper carbonate to the acid. Stir the mixture. When the reaction stops add a little more copper carbonate.

4 Stop adding copper carbonate when there is no sign of any further reaction.

5 Weigh the mass of the copper carbonate that you have left.

6 Pour the solution you have made into a crystallising dish. Write your name on it and keep it safe until a later lesson.

Results

Record the mass of copper carbonate weighed at the beginning, and that left at the end of the reaction.

Questions

1 How did you know when the reaction had been completed?

2 What mass of copper carbonate did you react with the sulfuric acid?

3 What is the relative formula mass of:

a) copper carbonate, CuCO3; b) copper carbonate, CuSO4?

4 The mass of copper sulfate formed in the reaction is given by the formula:

44 3

3

RFM of CuSOmass of CuSO mass of CuCO used

RFM of CuCO= ×

Calculate the mass of copper sulfate that you should have made in the experiment.

Extension (Higher tier only)

5 Write a balanced equation for the reaction of copper carbonate with sulfuric acid (H2SO4).

6 20 cm3 of sulfuric acid solution contains 0.196 g of sulfuric acid. What mass of copper carbonate should have completely reacted with this amount of sulfuric acid?




Technician sheet



� 100 cm3 measuring cylinder

� small beaker

� crystallising dish

� spatula

� stirring rod

� copper carbonate powder

� sulfuric acid (1 mol dm−3)

� access to a balance reading to 0.01 g

Method

Full instructions are given on practical sheet c6_04.

Notes

� It is important that students add very small amounts of the powder to the acid and check that the reaction is taking place. The reaction will become very slow before it reaches completion. Warn the students to look very carefully for signs of a reaction. They should have about half of their original copper carbonate left at the end. After being weighed it can be returned to stock.

� The impure copper sulfate solution that students prepare needs to be named and kept for a later lesson, when it will be purified and the yield measured. Store the solutions and the crystals that form somewhere where they will not be disturbed.

� Make sure that students keep the data collected in this experiment for the future lesson.

Health and Safety

� Sulfuric acid is CORROSIVE. Copper carbonate is HARMFUL and copper sulfate is TOXIC. Students should wear goggles and a lab coat. All spillages must be reported.




You will need a copy of the Periodic Table.

1 Relative masses of substances

1 Use the Periodic Table to find the relative atomic masses of the following elements:

a) potassium, K ............. b) sulfur, S .................. c) zinc, Zn .................

d) bromine, Br ............... e) lead, Pb ..................

2 The relative atomic mass of the element manganese is 55. What does this tell us about manganese atoms?

.....................................................................................................................................

.....................................................................................................................................

3 Calculate the relative formula mass of the following compounds:

a) carbon dioxide, CO2 ................................................................................................

b) nitric acid, HNO3 ......................................................................................................

c) ammonia, NH3 .........................................................................................................

4 Calculate the relative formula mass of the following salts:

a) magnesium chloride, MgCl2 ....................................................................................

b) copper nitrate, Cu(NO3)2 .........................................................................................

c) potassium sulfate, K2SO4 .........................................................................................

2 How much can we make?

1 The equation for the reaction of calcium hydroxide with nitric acid is:

Ca(OH)2(s) + 2HNO3(aq) → Ca(NO3)2(aq) + H2O(l)

a) How many formula units of nitric acid react with one formula unit of calcium hydroxide?

b) How many molecules of water are formed for each formula unit of calcium hydroxide?

c) The RFM of nitric acid is 63 and the RFM of water is 18. What mass of water is formed if:

(i) 63 g of nitric acid react completely

(ii) 126 g of nitric acid react completely

(iii) 6.3 g of nitric acid react completely?

c6_04 Reacting amounts continued


2 A chemical manufacturer wants to make the salt called barium chloride for use in analysis. The chemists decide to react barium carbonate with hydrochloric acid. The equation for the reaction is:

BaCO3(s) + 2HCl(aq) → BaCl2(aq) + H2O(l) + CO2(g)

a) What is the formula of barium carbonate?

b) What is the RFM of (i) barium carbonate, (ii) barium chloride?

c) The manufacturer wants to make 500 kg of barium chloride. What mass of barium carbonate is needed?

The formula to use is:

RFM barium carbonatemass of barium carbonate = × mass of barium chloride

RFM barium chloride

3 The chemists do some tests using 1.00 g of barium carbonate. In three tests, the masses of barium chloride made were 0.97 g, 1.02 g and 0.99 g. Why are these results all different?

3 Predicting quantities (Higher tier only)

1 In a reaction to make potassium nitrate starting with potassium hydroxide and nitric acid, 2.8 g of potassium hydroxide was completely reacted with dilute nitric acid. The equation for the reaction is:

KOH(s) + HNO3(aq) → KNO3(aq) + H2O(l)

a) What mass of nitric acid would be needed to react with the potassium hydroxide?

b) Predict the amount of potassium nitrate that should be formed in the reaction.

c) Suggest reasons why the amount of potassium nitrate actually produced is unlikely to be exactly the same as your answer to part (b)?

2 A chemical manufacturer is producing silver sulfate, Ag2SO4, by reacting silver oxide, Ag2O, with sulfuric acid.

a) Write a balanced chemical equation for the reaction.

b) Calculate the mass of silver oxide needed to produce 300 kg of silver sulfate.



c6_05 Neutralisation reactions

Resources

Student Book pages 172−173 � Interactive Book: Matching pairs ‘Planning and carrying out a synthesis’; Quick starter ‘Performing a titration’ � Homework pack c6_05


Equipment for demonstration and practical

Learning outcomes C6. 1.17 recall that the reaction of an acid with an alkali to form a salt is a neutralisation reaction

C6.2.11 describe how to carry out an acid-alkali titration accurately, when starting with a solution; making up of

standard solutions is not required

C6.2.12 substitute results in a given mathematical formula to interpret titration results quantitatively

Ideas about Science IaS 1.4 the mean of several repeat measurements is a good estimate of the true value of the quantity being

measured

IaS 1.5 from a set of repeated measurements of a quantity, it is possible to estimate a range within which the true

value probably lies

IaS 1.6 if a measurement lies well outside the range within which the others in a set of repeats lie, or is off a graph

line on which the others lie, this is a sign that it may be incorrect. If possible, it should be checked. If not, it should

be used unless there is a specific reason to doubt its accuracy

Literacy focus: Following written instructions.

Numeracy focus: Carrying out calculations using experimental data, including finding the mean and the range.

ICT focus: Logging and storing data; using sensors and dataloggers to monitor neutralisation reactions.


� recall which reactions are neutralisation reactions

� carry out an acid–alkali titration

� interpret the results of acid–alkali titrations

Key vocabulary

neutral �� neutralisation �� end-point �� titration �� range �� variation �� true value �� outlier �� mean


Carrying out titrations requires considerable manual dexterity and coordination. Students need time to become

familiar with handling the apparatus and to build up skills.


� Ask students to state what is formed when the following reactants are mixed together : sodium hydroxide/sulfuric

acid – sodium sulfate and water: potassium hydroxide/hydrochloric acid – potassium chloride and water –

calcium hydroxide/nitric acid – calcium nitrate and water. Ask students to suggest ways of showing that the

reaction has taken place – evaporate the water, use an indicator/pH meter.

Learning activities practical c6_05 Low demand � Ask students to explain what they understand by the terms ‘neutral’ and ‘neutralisation’.

Demonstrate a simple neutralisation reaction (see the technician sheet). Ask students what is in the beaker after

each addition of the acid. Make sure students understand that the indicator changes only when one reactant has

been neutralised by the other and at this point it is neither acid nor alkali. Explain that we can find the volumes of

acid and alkali that neutralise each other accurately by doing a titration. Go through the method on the practical

sheet, in particular demonstrating the use of pipette, filler and burette. Students should then carry out the

procedure as many times as possible in the time available and answer questions 1 to 4 on the practical sheet.

Teaching and learning notes: Students may have met neutralisation previously – assess their understanding and

correct any misconceptions.

Standard demand � Discuss what is happening in a neutralisation reaction with an indicator present and then go

through the procedure for titration. Further notes on technique, plus an example results table, are given on the

technician sheet. Each pair or group of students should then collect three or four sets of results. Discuss how size

c6_05 Neutralisation reactions continued


of variation and range in measurements affects confidence in the closeness of the mean to the true value and how

they should treat outliers. Students should do questions 1 to 8 on the practical sheet. If time allows and the

necessary equipment is available, demonstrate how a titration can be carried out using a pH meter/sensor and a

datalogger. Note the rapid change of pH at the end-point.

Teaching and learning notes: If students do not have enough to time to get a full set of results then they can

discuss whether or not class results can be combined reliably.

High demand � Following on from the titration, discuss the relationship between the volumes of reactants and the

equation for the reaction. Note that the volumes (and masses) of the reactants are always in proportion if the same

solutions are used. Combine the use of a given formula from the previous lesson with the titration results to

calculate reacting quantities (see practical sheet). Students should answer all the questions on the worksheet.

Plenary suggestions Ask students to compare their results with the rest of the class. Should they be the same or different? (If all have

used the same stock solutions and size of pipette then they should be the same). Can they explain the differences?

Sources of error – mistakes with the pipette and burette, not swirling the mixture, missing the end-point, misreading

the burette. If you want to make it competitive, see who has the smallest range and mean volume closest to the

true value (if you have time to measure it yourself).

Student Book answers Q1 a) Litmus turned red; b) Litmus changed colour; c) Litmus would stay blue.

Q2 a) Third value, 25.9 cm3; b) 24.9–25.2 cm

3; c) 25.0 cm

3

Q3 a) They have the same concentration; there is the same number of formula units of HCl and NaOH in the same

volume.

b) (i) 100.0 cm3; (ii) 1.5 dm

3

Practical sheet answers Q1 Gives a more accurate (precise) measurement of a particular volume of solution (than a beaker or measuring

cylinder); typically to 0.05 cm3 if used correctly.

Q2 Sodium chloride; water; indicator

Q3 To get a more accurate (precise) measurement for the volume of hydrochloric acid needed; to get as close to

the true value of the volume needed to neutralise the sodium hydroxide as possible.

Q4 To make the data more reliable; reduce uncertainty in the data; to find out if any measurements are outliers.

Q5 Check student’s answer.

Q6 a) Check student’s data; the first result is probably an outlier as it is usually a trial run.

b) The first measurement was not as careful as the rest so is likely to have errors; if the outlier is significantly

different to the others then there may have been obvious errors.

c) If the source of the error can be accounted for, then the outlier can be discarded; if not then it should be

retained.


Q8 Check student’s answer against their range; the smaller the range the more confident they can be.

Extension

Q9 Check student’s answer; (i) 5 × mean volume of acid; (ii) 50 × mean volume of acid.

Q10 Check student’s answer; if both solution concentrations are around 0.1 mol dm−3

, the answer should be 4 g.




P Acid–alkali titration

Objectives


� collect and interpret data on the neutralisation of an alkali by an acid.

Although the acid and alkali solutions are dilute, they can still irritate the eyes – wear goggles. Indicator solutions are TOXIC and FLAMMABLE.


beakers • conical flask • pipette and filler • burette and stand • small funnel • white tile

• sodium hydroxide solution • hydrochloric acid solution • indicator solution (with dropper) • distilled water

Method

1 Collect about 100 cm3 each of the sodium hydroxide solution and hydrochloric acid solution in separate beakers. Make sure you do not mix the beakers up.

2 Use a pipette and a filler to measure a quantity of sodium hydroxide solution. Empty the pipette into a clean conical flask. Record the volume of the pipette.



3 Add a few drops of the indicator solution to the conical flask. Swirl the flask to mix the indicator with the sodium hydroxide solution and note the colour.

4 Make sure that the burette is clean and that its tap is closed. Put the small funnel in the top of the burette and fill it with hydrochloric acid solution. Open the tap to let acid run into the jet. Clamp the burette vertically in a stand and record the level of the acid in the burette.

5 Put the conical flask under the jet of the burette. Open the burette tap and run hydrochloric acid into the conical flask. Swirl the conical flask constantly to mix the reactants. Close the tap as soon as the indicator colour changes.

6 Record the reading on the burette.

7 Empty the conical flask and wash it with distilled water.

8 Repeat steps 1 to 6 at least three more times. When you think you are getting close to the end-point (the colour change) in step 5, reduce the flow from the burette to single drops and swirl the conical flask after each drop – this allows a more accurate end-point to be found.

Results

Record all the measurements taken in a suitable table.

Questions

1 Why is a pipette used to measure out the sodium hydroxide solution?

2 The word equation for the reaction is:

sodium hydroxide + hydrochloric acid → sodium chloride + water

What is in the conical flask at the point when the indicator changes colour?

3 Read step 8 of the method again. Why is the hydrochloric acid added one drop at a time?

4 Why should the titration be repeated three or four times?

5 What is the range of your results?

6 a) Which of your results, if any, are outliers?

b) Can you give a reason why they are outliers?

c) What are you going to do with the outliers?

7 Calculate the mean of your data.

8 How confident are you that your mean is close to the true value?

Extension

9 Using your data, what volume of the same hydrochloric acid would react with the following volumes of the same sodium hydroxide solution:

a) 5 cm3; b) 50 cm3?

10 Use the formula below to calculate the mass of sodium hydroxide in 1 dm3 of your sodium hydroxide solution:

mass of NaOH in 1 dm3 of solution = 4 × volume of HCl (cm3)

volume of NaOH (cm3)




Technician sheet



� measuring cylinder (50 or 100 cm3)

� 2 beakers (100 or 250 cm3)

� conical flask (100 or 250 cm3)

� pipette (10, 20 or 25 cm3) and appropriate filler

� burette (50 cm3) and stand

� small funnel

� white tile (optional)

� sodium hydroxide solution (about 200 cm3, approximately 0.1 mol dm−3)

� hydrochloric acid solution (about 200 cm3 standard 0.1 mol dm−3)

� indicator solution with dropper – many indicators are suitable but methyl orange or phenolphthalein are most commonly used

� distilled water

Method

Full instructions for the class practical are given on practical sheet c6_05, but see additional notes here (next sheet).

Demonstration: Neutralisation

1 Pour about 20 cm3 of sodium hydroxide solution into a beaker, and a few drops of an indicator. Note the colour.

2 Add hydrochloric acid to the beaker a little at a time, swirling the beaker on each addition until the colour changes.

3 Add a little more acid and show that the colour does not change again.

Demonstration: pH titration

1 Use a suitable pipette to measure out 10 cm3 of sodium hydroxide solution into a small beaker.

2 Put a calibrated pH sensor in the beaker and stir it until a stable pH measurement is obtained.

3 Fill a burette with the hydrochloric acid.

4 Add the acid to the beaker 1 cm3 at a time. Stir the mixture and record the pH.

5 Continue adding hydrochloric acid until well past the end-point. If time allows, the addition of hydrochloric acid can be reduced to smaller quantities close to the end-point.

6 Plot a graph of pH against volume of hydrochloric acid added. A datalogger may do this in real time.



Notes

� Filling a pipette – Use an appropriate filler for the pipette. First wash out the pipette with water, and finally with the solution to be measured out. The pipette should be held close to the top when inserting it in the filler. Hold the bottom of the pipette away from the bottom of the beaker of solution when filling. Fill slowly so that air isn’t sucked into the filler. When the pipette is filled adjust the level so that the meniscus of the solution is on the mark. Let the solution flow out of the pipette into the conical flask naturally. Pipettes are designed to retain a final drop in the jet.

� Filling a burette – It is best if a small funnel is placed in the burette to avoid spillage when filling. Wash the burette with the solution that is to be titrated. The tap must be closed when filling but open it at some stage to allow the solution to fill the jet. Do not run the solution back into the stock beaker, because it may have been contaminated. When the burette is filled, clamp it in a vertical position and remove the funnel. Read the scale on the burette against the bottom of the meniscus of the solution. It is not necessary to fill the burette exactly to the 0 cm3 mark. The volume of solution run out of the burette is the difference between the first and final reading.

� Carrying out a titration – The first titration is usually a rough measurement, and so the solution can be run in from the burette relatively quickly with swirling until the end-point is reached. In subsequent titrations, the solution can be added from the burette one drop at a time close to the expected end-point. The burette can be read to ±0.05 cm3. A white tile on the burette stand provides a better contrast for seeing the colour of the indicator in the conical flask. Gently swirl the conical flask throughout the titration to ensure that the reactants are thoroughly mixed. Look for a permanent colour change after each addition of one drop of solution from the burette close to the expected end-point.

Health and Safety

� The sodium hydroxide solution and hydrochloric acid are dilute and not particularly hazardous, but can still irritate eyes – so students should wear goggles. Indicators are often TOXIC and, because they are usually in solution in ethanol, are FLAMMABLE.

Suggested results table

Volume of sodium hydroxide solution used (cm3) Titration number

1 2 3 4

Reading on burette at the end-point

Reading on burette at start of titration

Volume of hydrochloric acid used (cm3)

Tick if used in calculating the mean



c6_06 Explaining neutralisation

Resources



Equipment for demonstration and practical

Learning outcomes C6. 1.18 explain that acidic compounds produce aqueous hydrogen ions, H

+(aq), when they dissolve in water

C6.1.19 explain that alkaline compounds produce aqueous hydroxide ions, OH−(aq), when they dissolve in water

C6.1.20 write down the name of the salt produced given the names of the acid and alkali

C6.1.21 write down the formula of the salt produced given the formulae of the acid and alkali

C6.1.22 explain that during a neutralisation reaction, the hydrogen ions from the acid react with hydroxide ions from

the alkali to make water: H+(aq) + OH

−(aq) → H2O(l)

C6.2.11 describe how to carry out an acid-alkali titration accurately, when starting with a solid to be dissolved to

make up a solution; making up of standard solutions is not required

Ideas about Science IaS 1.4 the mean of several repeat measurements is a good estimate of the true value of the quantity being

measured


value probably lies




Literacy focus: Explaining ideas about acidity.


ICT focus: Logging and storing data; using sensors and dataloggers to monitor neutralisation reactions.


� name salts given the names of acids and alkalis

� explain neutralisation as the reaction between hydrogen ions and hydroxide ions

� write formulae of salts

Key vocabulary

ionic equation


The names of most acids do not reveal that they contain hydrogen, and many students have difficulty in

remembering to change the ending from the acid to the salt.


� Display the solid sodium hydrogen carbonate that the students will be using in the practical activity. Inform them

that this is a substance used as a remedy for acid indigestion. Ask students to plan what they must do to find out

how much of the stomach acid can be neutralised by a small sample of sodium hydrogen carbonate. Later they

can check their plans against the instructions on the practical sheet.

Learning activities worksheet c6_06 + practical c6_06 Low demand � Show students some bottles of acids with the formulae on the labels and ask them what they have

in common. If necessary, guide them to the presence of ‘H’ in all the formulae. Similarly bottles of alkalis all have

hydroxide, ‘OH’, in their formulas. Hence see if students can deduce what happens in neutralisation reactions –

water is formed. Perhaps using cards or a whiteboard show that the other ‘bits’ of the acid and alkali form the salt.

For example, hydrochloric acid + sodium hydroxide – take the ‘hydro’ from the acid and add it to the ‘hydroxide’ to

make water leaving ‘sodium’ and ‘chloric’, which changes to ‘chloride’ when they are put together. Get the students

to try a few more examples. Students should then have a go at the titration activity on the practical sheet.

Teaching and learning notes: Students need to recall the different endings of the acids and the salts – e.g.

sulfuric acid forms sulfates.

c6_06 Explaining neutralisation continued


Standard demand � Explain (Arrhenius’ theory) that acids and alkalis are made up of ions in solution and that

neutralisation involves the combination of hydrogen ions and hydroxide ions to form water molecules, leaving the

cation and anion in solution as the salt. Use cards, a whiteboard or an animation to demonstrate this – e.g. mix up

H+

, Cl−, Na

+ and OH

− ions then join the H

+ and OH

− together to form water leaving the Na

+ and Cl

−. Students

should then do the titration activity reinforcing their interpretation of data and understanding of neutralisation. If

there is time, the use of a pH meter/sensor and datalogger can be demonstrated to carry out the experiment, or, if

there is sufficient equipment, the investigation can be modified as a pH titration.

Teaching and learning notes: Students will need to realise that all neutralisation reactions are the same and that

the only reaction taking place is between the H+

and OH−.

High demand � (Higher tier only) Put greater emphasis on the formulae of ions drawing attention to double (and

triple) charged ions. Note how the given formulae of an acid and an alkali allow the correct formula of the salt to be

worked out. Activity 3 on the worksheet gives further practice at this.

Plenary suggestions Students compare the results of their investigation and comment on the sources of error, particularly in making up

the standard solution of sodium hydrogen carbonate – e.g. powder lost after weighing, solution splashed or spilled

during dissolving or transfer to volumetric flask; not fully dissolved (unlikely in this case); some solution left in

beaker; solution not shaken (for long enough).

Student Book answers Q1 ‘H’/hydrogen atoms in the formula.

Q2 a) (i) zinc chloride; (ii) magnesium sulfate; b) water

Q3 a) H+(aq) + OH

−(aq) → H2O(l); b) potassium ions; nitrate ions

Q4 The pH starts low because the acid solution contains H+ ions; as the alkali is added the OH

− ions react with the

H+

ions so the there are fewer H+ ions in solution; so the pH rises.

Q5 a) MgCl2; b) Cu(NO3)2; c) K2SO4


Q1 a) (i) Sodium sulfate; (ii) potassium nitrate ; (iii) magnesium chloride; b) water

Q2 Hydrogen


Q1 Solutions are acidic if they contain hydrogen ions, H+;

solutions are alkaline if they contain hydroxide ions, OH−

Q2 H+(aq)

+ OH

−(aq) → H2O(l)

Q3 Weigh a tablet and dissolve it in distilled water to make a named volume of solution; titrate this solution with a

measured volume of stomach acid solution.


Q1 a) calcium chloride, CaCl2; b) potassium sulfate, K2SO4

c) magnesium nitrate, Mg(NO3)2; d) sodium phosphate, Na3PO4

Practical sheet answers Q1 To make sure that the solid is dissolved in known a volume of solution.

Q2 Three or four; to ensure that the results are reliable.

Q3 Alkaline/an alkali

Q4 Student’s results; they should explain why they have discarded or used outliers.

Q5 10 × the mean volume from the student’s titration (if a 10 cm3 pipette has been used for the stomach acid).

Q6 Answers should be around 4 g.



c6_06 Investigating neutralisation

P Antacids

Objectives


� collect and interpret data on the reaction of sodium hydrogen carbonate with stomach acid.

‘Stomach acid’ contains hydrochloric acid. In this experiment you will make up a solution containing a known amount of sodium hydrogen carbonate, which is used in antacid remedies and forms an alkaline solution that can neutralise ‘stomach acid’.

The solutions are dilute and not hazardous but can irritate eyes, so wear goggles. Indicator solutions are TOXIC and FLAMMABLE.


beakers • conical flask • pipette and filler • 100 cm3 volumetric flask • burette and stand

• small funnel • white tile • spatula • weighing boat • access to a balance

• sodium hydrogen carbonate • hydrochloric acid solution

• methyl orange indicator (with dropper) • distilled water

Method

Soothes acid indigestion

TUMMIES Contains: sodium hydrogen carbonate

24 tablets

c6_06 Investigating neutralisation continued


1 Weigh out accurately about 1 g of sodium hydrogen carbonate. Record the mass of solid used.

2 Put the sodium hydrogen carbonate in a clean beaker and add about 50 cm3 of distilled water. Stir the mixture until the solid dissolves. Pour the solution into a volumetric flask.

3 Pour about 20 cm3 of water into the same beaker; swirl it around and then add this solution to the volumetric flask.

4 Add distilled water to the volumetric flask to make the solution up to the mark. Fit a bung tightly and shake the flask gently.

5 Fill a burette with the sodium hydrogen carbonate solution and clamp the burette vertically in a stand.

6 Collect the ‘stomach acid’ in a beaker and transfer a pipette-full to a conical flask using a pipette filler.

7 Add a few drops of methyl orange indicator to the conical flask. Swirl the flask and note the colour of the indicator.

8 Put the flask under the burette tap. Titrate the sodium hydrogen carbonate solution into the conical flask until the end-point is reached. Record the volume of solution used.

9 Repeat the titration using the same pipette to measure out the stomach acid. Top up your burette with sodium hydrogen carbonate solution when necessary.

Results

Record all your data in a suitable table.

Questions

1 Why was a volumetric flask used to make up the solution of sodium hydrogen carbonate?

2 How many times did you do the titration? Why did you choose this number?

3 Sodium hydrogen carbonate neutralises stomach acid. What type of substance is sodium hydrogen carbonate solution?

4 What is the mean and the range of your titration results? Explain how you dealt with any outliers.

5 How much of your sodium hydrogen carbonate solution would be needed to neutralise 100 cm3 of stomach acid?

6 Calculate the mass of hydrochloric acid in 1 dm3 of the stomach acid using the formula:

( ) ( )( )

3

33 3

3

mass of hydrochloric acid in 1 dm of stomach acid

365 mass of NaHCO g volume of NaHCO cm=

84 volume of stomach acid cm

× ×

×



c6_06 Investigating neutralisation

Technician sheet


Demonstration

� bottles of acids and alkalis labelled with names and formulae

� pH meter/sensor

� data logging equipment if available

� buffer solutions

Practical


� beakers (100 cm3 or 250 cm3)

� conical flask (100 cm3 or 250 cm3)

� pipette (preferably 10 cm3 but 20 or 25 cm3 can be used)

� appropriate filler

� burette (50 cm3)

� stand

� small funnel

� white tile (optional)

� sodium hydrogen carbonate (about 1 g)

� hydrochloric acid (0.1–0.15 mol dm−3) labelled ‘stomach acid’

� methyl orange indicator

� distilled water

� access to a balance reading to 0.01 g

Method

Full instructions for the class practical are given on practical sheet c6_06.

Demonstration: pH titration

1 Use a suitable pipette to measure out 20 or 25 cm3 of hydrochloric acid into a small beaker.

2 Put a calibrated pH meter/sensor in the solution and stir it until the pH is stable.

3 Fill a burette with the sodium hydrogen carbonate solution.

4 Add the solution from the burette to the solution in the beaker 1 cm3 at a time. Stir the mixture and record the pH after each addition.

5 Continue until well past the end-point. If time allows, the addition of the solution can be reduced to smaller quantities close to the end-point.

6 Plot a graph of pH against volume of sodium hydrogen carbonate added. A data logger may do this in real time.

c6_06 Investigating neutralisation continued


Notes

� The sodium hydrogen carbonate will fizz during the reaction because of the release of carbon dioxide. The reaction is not as simple as that between an acid and a metal hydroxide, but the alkali metal hydroxides that are soluble are caustic in the solid state and should not be handled by students. Other basic metal oxides are not sufficiently soluble for a simple class experiment.

� Advise students that they do not have to weigh out exactly 1.00 g of sodium hydrogen carbonate, but they do need to know the mass they are using to 2 d.p.

� With the time taken to make up the solution there may not be enough time in a lesson for students to complete three or four titrations. They should do the calculation using the results they do have and compare their conclusions with the rest of the class to assess the confidence in their result.

� Real stomach acid is more concentrated than the solution used in this experiment.

Health and Safety:

� The sodium hydrogen carbonate and hydrochloric acid are dilute and not particularly hazardous, but can still irritate eyes, so students should wear goggles. Indicators are often TOXIC and, because they are usually in solution in ethanol, are FLAMMABLE.

Suggested results table

Volume of stomach acid solution (cm3)

Titration number 1 2 3 4

Reading on burette at the end-point

Reading on burette at start of titration

Volume of sodium hydrogen carbonate

solution used (cm3)

Tick if used in calculating the mean



c6_06 Explaining neutralisation

1 It’s the water

1 a) What salts are formed when neutralisation reactions take place between the following reactants:

(i) sodium hydroxide and sulfuric acid ......................................................................

(ii) potassium hydroxide and nitric acid ....................................................................

(iii) magnesium hydroxide and hydrochloric acid? ...................................................

b) What other substance is formed in each of the reactions? .......................................

2 What element must be in citric acid for it to be an acid? ...............................................

2 Ions combine

1 Explain what makes a solution acidic or alkaline.

2 Write down the ionic equation for the reaction that takes place when sodium hydroxide solution reacts with nitric acid.

3 ‘Tummies’ is a remedy that people take for ‘heartburn’ – it is supplied in tablet form. Describe how you could find out how much stomach acid can be neutralised by one ‘Tummies’ tablet.

3 Formulae of salts (Higher tier only)

Write the name and the formula of the salts formed when the following reactants neutralise each other:

a) Ca(OH)2 and HCl

b) KOH and H2SO4

c) Mg(OH)2 and HNO3

d) NaOH and H3PO4 (phosphoric acid)



c6_07 Energy changes in reactions

Resources

Student Book pages 176−177 � Interactive Book: Naked Scientist animation ‘What are catalysts?’; Practical investigations ‘Weak and strong’ � Homework pack c6_07


Warmers and coolers that involve chemical reaction; equipment for demonstrations and practicals

Learning outcomes C6.1.23 understand the terms endothermic and exothermic

C6.1.24 use and interpret simple energy level diagrams for endothermic and exothermic reactions

C6.1.25 understand the importance of the energy change during a reaction to the management and control of a

chemical reaction.


reactions), including: d. carrying out the reaction in suitable apparatus in the right conditions (such as temperature)


ICT focus: Using sensors and dataloggers.


� understand what is meant by exothermic and endothermic

� interpret energy diagrams for reactions

� understand the importance of the control of energy during chemical synthesis

Key vocabulary

exothermic �� endothermic �� energy level diagram �� heat exchanger


Students will have met the use of reactions as an energy source (e.g. combustion) but it can be difficult to

appreciate that the reactants of such reactions are themselves losing energy.


� Demonstrate a spectacular exothermic reaction, such as the thermite reaction or aluminium and iodine

(technician sheet). Ask students to report observations (including heat given off) and ask them to explain where

the energy comes from.

Learning activities worksheet c6_07 + practical c6_07 Low demand � Demonstrate some simple exothermic and endothermic reactions (see the technician sheet) and

get students to link the terms ‘exothermic’ and ‘endothermic’ to the respective warming and cooling effects. Ask

students to suggest uses of such reactions: e.g. exothermic – keeping warm (hand-warmers), cooking, conversion

to other forms of energy (electricity, light); endothermic – keeping cool in hot countries, soothing burns, cooling

drinks, preserving food, making ice cream. Demonstrate the use of warmers or coolers that are available and ask

students to describe and explain what is happening. (Note that these may involve a chemical reaction or a physical

change such as melting.) Students should then carry out the practical activity to measure some energy changes

and answer questions 1–4. There are additional activities on the worksheet.

Teaching and learning notes: Make sure students do not confuse the terms ‘exothermic’ and ‘endothermic’. A

mnemonic or memorable picture (e.g. explosion = exothermic) may be useful.

Standard demand � Introduce the concept of a ‘closed system’ – one in which materials and energy are contained

as changes take place. Students should carry out the practical activity to measure temperature changes and

answer questions 1–4. Then discuss energy transfer and explain that a temperature change in the surroundings –

the water in a test tube – implies a change in the energy of the reacting particles. Hence lead on to energy

diagrams. Suggest that the size of the energy gap can be related to the amount of energy involved in the reaction.

Students can then answer question 5 on the practical sheet. There are more examples for students to interpret on

the worksheet.

Teaching and learning notes: Students will need to appreciate the difference between ‘temperature’ and ‘heat

energy’. The same quantity of reactants will always release or absorb the same amount of heat energy, but the

temperature change will depend on the surroundings.

c6_07 Energy changes in reactions continued


High demand � Higher attaining students can also answer question 6 on the practical sheet. Then ask students to

list reasons why chemical engineers should be interested in the energy changes of a reaction – e.g. dangers of

overheating; insufficient energy for reaction to occur; waste of energy lost to the environment. Note that the solution

to some of these concerns is the heat exchanger (Student Book p. 177) and explain that most of the pipes and

equipment seen in pictures of chemical factories are concerned with moving heat (as steam or hot water) from one

place to another. Discuss the importance of heat exchangers – famous nuclear accidents such as (Chernobyl,

Ukraine and Fukushima, Japan) were caused by a failure of heat exchangers.

Plenary suggestions Ask students to give examples of exothermic and endothermic changes. As well as those experienced in the

lesson, allow appropriate changes of state and other combustion reactions, acid/base reactions etc. They could be

asked to suggest energy level diagrams for those not already drawn.

Student Book answers Q1 Cooler

Q2 The temperature increases; exothermic reaction.

Q3 Reactants energy level above the products energy level.

Q4 It increases.

Q5 Overheating could cause an explosion; waste of energy that could be used elsewhere.

Q6 Whether the reaction is exothermic or endothermic; how much heat energy is given out or needed for a specific

amount of reactant.

Fit temperature-monitoring devices to the reaction vessel; design a heat exchanger to remove heat produced;

and to carry it to where it can be used.


Q1 Exothermic; the surroundings get warmer.

Q2 Endothermic; heat is supplied.

Q3 Iron filings react with the water (and oxygen) (forming rust); this is an exothermic reaction that gives out heat (to

the surroundings).


Q1 1 Wood and oxygen higher than the products; (carbon dioxide and water).

2 Iron oxide and carbon lower than products; (iron and carbon dioxide).

3 Iron filings and water higher than products; (iron oxide).

Q2 Quantities of reactants; the reaction (how exothermic it is); the size of the container.


Q1 Burning fuel is an exothermic process; the hot gases formed heat up water in the heat exchanger; the waste

gases are cooled and escape from the flue; the hot water is pumped through the radiators around the house;

the hot water warms the air in the house ; it cools and is returned to the heat exchanger.

Q2 An arrangement which heats the reactant gases before entering the reaction vessel and which removes heat

from the reaction vessel itself; the two process are preferably linked so that the heat of the reaction is used to

heat up the reactant gases.

Practical sheet answers Q1 To stop heat entering and/or leaving the reaction mixture.

Q2 Exothermic; the temperature rises.

Q3 Endothermic; the temperature falls.


Q5 Reaction1 – reactants line above products line; Reaction 2 – products line above reactants line; energy

changes marked.

Extension

Q6 a) Very much the same; the reactants give out more heat but it is spread around more water.

b) About twice what they recorded; there is twice as much reactant giving out twice as much heat energy; which

is taken in by the same amount of water as before.




P Measuring temperature changes in reactions

Objectives


� collect and interpret temperature changes in reactions.

The hydrochloric acid and sodium hydroxide used in this experiment are CORROSIVE. Wear goggles and avoid contact with the skin. Report all spillages immediately. Citric acid is an eye IRRITANT.


polystyrene cups • measuring cylinder • stirring rod

• thermometer (or temperature sensor and datalogger)

• hydrochloric acid solution • sodium hydroxide solution • sodium hydrogen carbonate • citric acid

Use either method A or method B.

Method A: Measuring temperature changes using a thermometer

Reaction 1:

1 Measure 20 cm3 of each of hydrochloric acid and sodium hydroxide solutions into separate cups.

2 Use a thermometer to measure the temperature of the solution in each cup.

3 Mix the solutions together, stir well and measure the highest temperature reached.

4 Wash out the cups and repeat the experiment twice more.

Reaction 2:

1 Measure 50 cm3 of tap water into a cup and measure its temperature.

2 Put a spatula-full of each of solid sodium hydrogen carbonate and solid citric acid on a piece of paper and mix the powders together.

3 Add the mixture quickly to the water, stir well and record the lowest temperature reached.



Method B: Measuring temperature changes using a datalogger

Reaction 1:

1 Measure 20 cm3 of hydrochloric acid and sodium hydroxide solutions into separate cups. Check that the temperature of both solutions is the same.

2 Set the datalogger to take readings at frequent time intervals. Put the temperature sensor into one of the solutions and start the datalogger.

3 Add the solution from the second cup and stir the mixture.

4 Record the temperature data for 3 or 4 minutes and display it in table and graph form.

Reaction 2:

1 Measure 50 cm3 of tap water into a cup. Put the temperature sensor in the water and set the datalogger to record readings at frequent time intervals.

2 Put a spatula-full of each of solid sodium hydrogen carbonate and solid citric acid on a piece of paper and mix the powders together.

3 Start the datalogger and add the mixture quickly to the water and stir it well.

4 Record the temperature data for 3 or 4 minutes and display it in table and graph form.

Results

Record your data in a suitable table.

Questions

1 Why are expanded polystyrene cups used in this experiment instead of test tubes or glass beakers?

2 Is the reaction between hydrochloric acid and sodium hydroxide exothermic or endothermic? Explain your answer.

3 Is the reaction between citric acid and sodium hydrogen carbonate exothermic or endothermic? Explain your answer.

4 What are the temperature changes in the two reactions you have done. If you have repeated measurements give the mean and range of your results.

5 Draw energy level diagrams for the two reactions.

Extension

6 What do you think would happen to the temperature change in Reaction 1 if you used:

a) 50 cm3 each of the hydrochloric acid and sodium hydroxide solution

b) 20 cm3 each of solutions containing twice the amount of hydrochloric acid and sodium hydroxide?

Further activity: The cooler challenge

Using the apparatus provided and solid sodium hydrogen carbonate and solid citric acid, plan and test a method to cool 50 cm3 of water to 10 °C.




Technician sheet


Demonstration

� thermite reaction – large beaker or bucket, sand, filter papers, iron oxide and aluminium powder, magnesium ribbon and powder, barium nitrate

� aluminium–iodine reaction – 3 g aluminium powder, 5 g iodine, pestle and mortar, tin lid, tripod, warm water

� boiling tubes, spatula, magnesium ribbon, hydrochloric acid (1 mol dm−3), potassium chloride (powder)

� hand-warmers and self-heating cans; cold packs and coolers for picnic bags

Practical


� expanded polystyrene cups

� measuring cylinder (100 cm3)

� stirring rod

� thermometer (0–110 °C) or temperature sensor and datalogger

� 100 cm3 hydrochloric acid (1 mol dm−3)

� 100 cm3 sodium hydroxide solution (1 mol dm−3)

� sodium hydrogen carbonate (powder)

� citric acid (powder)

� access to a balance

Method

Demonstrations

Starter: thermite reaction – if a member, see CLEAPSS Guide L195.

Aluminium/iodine reaction: grind 2 g iodine to a powder using a mortar and pestle and then mix with 0.5 g aluminium powder (care!) and place the mixture on a heatproof mat in the fume cupboard. No reaction occurs until a drop of water (with a little detergent to assist wetting) is added. Then, after a delay, fumes will be emitted (mostly iodine).

Getting hot or cold: 1 Pour some hydrochloric acid into a boiling tube (about a quarter-full). Ask a (brave)

student (wearing goggles) to hold the bottom of the tube and drop in a piece of magnesium ribbon (about 4 cm). Ask the student to report what they feel.

2 Pour some cold water into a boiling tube (about a quarter-full). Ask a student (not so brave this time) to hold the bottom of the tube. Add a spatula of potassium chloride and stir. Ask the student to report what they feel.

Practical

Full instructions for the class practical are given on practical sheet c6_07. Alternative methods are provided for the use of thermometers or data logging equipment.



Notes

� When using a data logger, it is useful to continue recording the temperature until after the peak change – i.e. when the mixture has started to cool or warm again. If time is short, just wait until the temperature levels off. The maximum change can be calculated from the plot.

� In the suggested further activity, ‘The cooler challenge’, students have to find the quantities and proportions of sodium hydrogen carbonate and citric acid required to cool some water to as close to 10 °C as possible. This can either be a wild ‘trial and error’ activity or a more methodical process in which students weigh out the reactants and look for a correlation between quantity and temperature change. Some groups may want to know the ideal reaction ratios (the RFM of NaHCO3 is 84 and that of citric acid is 192; the molar ratio is 1 : 1, so the mass ratio is about 1 : 2). It is fun to have prizes for the groups who perform best.

� Hand-warmers can be made using a mixture of fine iron filings and salt. Sufficient water to moisten the mixture is added to initiate the reaction. The salt is a catalyst for the reaction of iron filings, water and oxygen. Some recipes include vermiculite to absorb the water and regulate the reaction.

Health and Safety

� The hydrochloric acid and sodium hydroxide solutions are CORROSIVE. Students should wear goggles and a lab coat. Disposable gloves may be worn. All spillages should be reported and cleared up immediately.

� The thermite and aluminium–iodine reactions are HAZARDOUS – if a member, see CLEAPSS Guide L195.

� Magnesium ribbon is FLAMMABLE.




1 Getting hot or cold

1 Is burning a log of wood an exothermic or endothermic change? Explain your answer.

......................................................................................................................................

......................................................................................................................................

2 In a blast furnace, iron oxide and carbon must be heated to over 1500 °C to make iron. Is this an exothermic or an endothermic process?

......................................................................................................................................

3 A pocket hand-warmer contains iron filings. The hand-warmer can be activated by adding water. Explain how the hand-warmer works.

......................................................................................................................................

......................................................................................................................................

2 Losing and gaining energy

1 Draw energy diagrams for the reactions in questions 1 to 3 above.

2 In a chemical factory, a reaction takes place in a closed metal container. The reaction is exothermic. What factors will affect the temperature reached inside the reaction vessel?

3 Managing energy changes

1 A domestic central heating boiler contains a ‘heat exchanger’. Explain how burning a fuel is used to heat the house.

2 In an industrial process, two gases react to make a product – and the reaction is exothermic. The reactants must be heated to start the reaction, but if the temperature rises any higher the product may decompose. How could chemical engineers design the process to ensure that the conditions are suitable for the reaction to take place? Draw a diagram to illustrate your answer.



c6_08 Separating and purifying

Resources


Files on Teacher Pack CD: c6_08_worksheet; c6_08 practical; c6_08 technician

Equipment for demonstrations and practicals

Learning outcomes C6. 2.2 understand the purpose of these techniques: dissolving, filtration, evaporation, crystallisation, drying in an

oven or desiccator

C6.2.3 understand the importance of purifying chemicals and checking their purity

C6. 2.10 calculate percentage yields given the actual and the theoretical yield


reactions), including: e. separating the product from the reaction mixture (limited to filtration), f. purifying the

product (limited to evaporation, crystallisation and drying in an oven or desiccator), g. measuring the yield and

checking the purity of the product (by titration)

Literacy focus: Following instructions, understanding use of terms ‘pure’ and ‘impure’.

Numeracy focus: Carrying out calculations to find percentage yield and calculate yield.


� understand methods of separating and purifying products of a chemical synthesis

� understand why the purity of a product is important

� calculate the percentage yield of product in a reaction

Key vocabulary

pure �� filtration �� dissolving �� filtrate �� evaporation �� crystallise �� dessicator


The use of the term ‘pure’ in everyday language can lead to misconceptions. Understanding the reasons for the

many steps in a purification process can be confusing.


� Display a variety of pure and impure substances. Ask students to classify them as pure and impure. Ask them to

explain their choices.

Learning activities worksheet c6_08 + practical c6_08 Low demand � Ask students to explain what they understand b y the terms ‘pure’ and ‘impure’. Note the difference

between the chemical terms and their use in everyday life (cf. pure fruit juice). Look at samples of pure and impure

sodium chloride. Ask students to give reasons why we need to know if a substance is pure or impure (e.g. drugs,

foods etc.). Discuss how pure salt could be obtained from the mixture. Explain the process of dissolving (impurities

insoluble), filtering (to separate liquids from solids), evaporating (to separate solvent from solute). Students may

then carry out the low demand practical activity P1 purifying salt and answer the questions. Activity 1 on the

worksheet gives further questions.

Teaching and learning notes: Students need to be able to recognise the difference between a pure compound

and a mixture. This relates to earlier work on compounds and elements.

Standard demand � Having introduced the ideas about pure and impure substances, go through the more

complex procedure for removing soluble and insoluble impurities from a salt (Student book p. 178). Show students

a desiccator with a drying agent (also found in biscuit tins and packaging for electronic components). They can

then carry out the procedure (P2 on the practical sheet) for separating pure copper sulfate from the impure

samples they prepared in practical c6_04. They should answer questions 1 and 2. Further questions are provided

in Activity 2 on the worksheet.

Teaching and learning notes: The practical activity is an exercise in following instructions and manual dexterity.

Make sure students follow the procedure in the correct order.

High demand � Explain the formula for calculating percentage purity. Students can then do the extension

questions on the practical sheet, calculating the percentage purity (using the data they obtained for the theoretical

c6_08 Separating and purifying continued


yield in practical c6_04). Discuss what the percentage yield shows: very low – a lot of material lost or wasted;

above 100% – sample is damp or still impure. Discuss how the purity can be confirmed – e.g. whether or not it

contains any acid or alkali. Remind students of the previous lesson’s work on titration and how this can be used to

find out how much acid or alkali is present. Students can do Activity 3 on the worksheet.

Plenary suggestions Play ‘plus’, ‘minus’, ‘question’ using the statement ‘A chemical manufacturer of 1 million tonnes of hydrochloric acid

has a % yield of 99%.’ Plus points – 99% seems pretty good; minus point – 10 000 tonnes of hydrochloric acid lost;

question – what happens to the hydrochloric acid that escapes?

Student Book answers Q1 A pure substance is a single substance; an impure substance is a mixture of two or more substances.

Q2 Place a folded filter paper in a filter funnel; pour the mixture into the funnel; the bits of sand will remain in the

filter paper; the salt solution will pass through.

Q3 More of the product will dissolve in warm water; insoluble impurities will not dissolve.

Q4 When water is evaporated the solution becomes more concentrated; until the product crystallises; the

concentration of the impurities will still be low so they stay in solution.

Q5 86%

Q6 98%


Q1 Should include: dissolving the impure baking soda in water; filtering to remove the chalk; evaporating the water

off. Answers suggesting heating the solution to dryness can be accepted even though sodium hydrogen

carbonate decomposes on heating.

Q2 Impurities may be toxic; harmful; interfere with the way the drug works.


Q1 Dissolve → filter → crystallise → filter → dry

Q2 Purification of the drug; measurement of purity; clinical testing of the drug and the impurities. Actually the active

enantiomer of thalidomide is changed into the harmful enantiomer in the body – but do not bring this up.

Q3 Dissolve a sample in water; test with indicator/pH meter

Q4 Dissolve a measured amount of the material in a known volume of water; titrate with a standard solution of an

alkali.


Q1 99%; Q2 a) 5.85 g; b) 89%

Practical sheet answers Purifying salt (Low demand)

Q1 It is a mixture of salt/ sodium chloride and other substances; it contains two or more substances.

Q2 The soluble salt dissolves; leaving the insoluble impurities as a solid.

Q3 Remain in the filter paper.

Q4 To separate the water from the salt.

Q5 Student’s observations

Purifying a salt (Standard and High demand)

Q1 a) To dissolve the salt as quickly as possible; leaving insoluble impurities as solids.

b) To separate the solution of the salt from the insoluble impurities.

c) To evaporate water from the solution so that the salt would crystallise.

d) To separate the crystals of the salt from the solution containing soluble impurities.

e) To dry the crystals.

Q2 Putting the crystals in a warm oven or a desiccator.

Extension

Q3 Waiting longer for more of the copper sulfate to crystallise from the solution.





P1 Purifying salt

Objectives


� use filtering and evaporating to purify a sample of salt.

Remember that apparatus that has been heated can stay hot for a long time.


impure salt • beaker • stirring rod • filter funnel and paper

• evaporating dish • tripod and gauze • Bunsen burner

Method

1 Put a spatula of the impure salt in a beaker.

2 Add about 20 cm3 of water and stir the mixture well.

3 Fold a piece of filter paper and put it in a filter funnel. Pour the mixture from the beaker into the filter paper. Collect the filtrate in an evaporating dish.

4 Put the evaporating dish and salt solution on a tripod and gauze. Heat the solution – take care because the solution will ‘spit’ as it boils.

5 When all the water has boiled off, turn the Bunsen burner off and let the evaporating dish cool down.

Results

Write down what you see at each stage of the method.

Questions

1 Why do we say that the salt is ‘impure’?

2 What happens when you add water to the impure salt?

3 What happens to the impurities when you filter the mixture?

4 Why did you heat the solution until it boiled dry?

5 Do you think you ended up with pure salt? Explain your answer.



P2 Purifying a salt

Objectives


� use separation techniques to separate a sample of a pure salt

� calculate the percentage yield of the salt.

You will need the sample and data from practical c6_04 Reacting amounts: making a salt.

Remember that apparatus that has been heated can stay hot for a long time. Copper sulfate is TOXIC. Wash your hands if you spill any on yourself.


beaker • stirring rod • filter funnel and paper • evaporating dish

• tripod and gauze • Bunsen burner • access to warm water

Method

1 Scrape the blue solid formed in the earlier experiment into a beaker. Add about 10 cm3 of warm water and stir well.

2 If the solid does not completely dissolve then add a little more water. Remember that some impurities may not dissolve.

3 Filter the mixture through a filter funnel and filter paper. Collect the filtrate in an evaporating dish.

4 Put the evaporating dish and solution on a tripod and gauze. Heat the solution.

5 When you see crystals starting to appear on the surface of the solution, stop heating.

6 Allow the evaporating dish to cool.

7 Wait as long as you can and then filter the mixture through a clean filter paper and funnel. Collect the solid copper sulfate in the filter paper.

8 Press the solid between two pieces of filter paper.

9 Scrape the solid into a weighing boat and weigh the solid.

Results

Record the appearance of the sample at the start and end and record the mass of product.

Questions

1 Explain why:

a) your sample was mixed with warm water (step 1)

b) the solution was filtered (step 3)

c) the solution was heated (step 4)

d) the solution was filtered again (step 7)

e) the sample was pressed between filter papers (step 8).

2 What would be a better method of drying your crystals?

Extension

3 How could you have improved your yield of solid copper sulfate?

4 Calculate the percentage yield of copper sulfate using the formula:

actual yield% yield = 100%

theoretical yield×

[Note: your theoretical yield was calculated in question 4 of practical sheet c6_04.]

5 Explain why your percentage yield is not 100% – or even close to it.




Technician sheet


Demonstration:

� samples of pure and impure materials:

pure – distilled water, metals (copper, magnesium), sodium chloride and other salts

impure – mixture of salt and sand, solutions, soda water, orange juice, rocks, cakes

� desiccator with drying agent

Practicals:

P1: Purifying salt (Low demand)


� beaker and stirring rod

� filter funnel and paper

� evaporating dish

� tripod and gauze

� Bunsen burner

� impure salt (50 : 50 mixture of sodium chloride and powdered charcoal or sand)

P2: Purifying a salt (Standard and High demand)


� beaker and stirring rod

� filter funnel and paper


� tripod and gauze

� Bunsen burner

� access to warm water

� samples of copper sulfate from practical c6_04 Method

Full instructions for the activities are given on practical sheet c6_08.

Notes

� There will not be time to allow the copper sulfate to crystallise fully. Make sure that crystals are already forming on the surface when the solution is being heated. Allow as long as possible for the crystals to form before the students filter them off. There will not be time for drying the crystals in an oven or desiccator, so they should be dried between filter papers before weighing them. Their percentage yield should be considerably less than 100%. It may be high if the crystals were not dried properly.

� If students have not retained their samples from the earlier activity they can use stock copper sulfate for the purification process but will not be able to calculate percentage yield.

Health and Safety

� Copper sulfate is TOXIC. All spills should be reported and cleaned up. Do not dispose of copper sulfate down the drain (samples can be kept for other experiments).

Remind students that the tripod, gauze and evaporating dish will remain hot for some time after heating.




1 The importance of purity

1 ‘Cupcakes Ltd’ found that a batch of the baking soda (sodium hydrogen carbonate) that they used had become mixed with some chalk. Write a letter to the manager of suggesting how they could separate the baking soda from the chalk. Baking soda is soluble in water and chalk is insoluble.

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2 ‘Alpha Drugs Ltd’ have developed a process for making a new drug to cure the common cold. Explain why is it important that the drug is pure before it is sold.

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2 Crystallisation

1 Draw a flow chart describing the procedure for removing insoluble and soluble impurities from a soluble salt.

2 In the 1960s thalidomide was given to some pregnant women to help with ‘morning sickness’. An impurity in the drug was discovered to be the cause of dreadful deformities in their babies. What steps should have been taken to find out if the drug was safe to use?

3 How could you show that a sample of a salt contained an acidic impurity?

4 How could you find out how much of an acidic impurity was present in a sample of a salt?

3 Percentage yield

1 A chemical manufacturer uses enough raw materials to make 200 000 tonnes of sodium hydroxide, but at the end of the process finds that they have only 198 000 tonnes of the pure compound. What was the percentage yield?

2 Sam and Josie use a solution containing 4 g of sodium hydroxide to react with hydrochloric acid to make sodium chloride. When they have separated out the pure sodium chloride they find they have made 5.2 g.

The equation for the reaction is:

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

(Relative atomic masses: Na = 23, O = 16, H = 1, Cl = 35.5)

a) What was the theoretical yield of Sam and Josie’s sodium chloride?

b) What was their percentage yield?



c6_09 Measuring rates of reactions

Resources

Student Book pages 182−183 � Interactive Book: Quick starter ‘Getting a good yield’ � Homework pack c6_09


Equipment for demonstrations and practicals

Learning outcomes C6. 2.13 understand why it is important to control the rate of a chemical reaction (to include safety and economic

factors)

C6.2.14 explain what is meant by the term ‘rate of chemical reaction’

C6.2.15 describe methods for following the rate of a reaction (for example, by collecting a gas, weighing the

reaction mixture or observing the formation or loss of a colour or precipitate)

C6.2.16 interpret results from experiments that investigate rates of reactions

Ideas about Science IaS 1.1 data are crucial to science. The search for explanations starts from data; and data are collected to test

proposed explanations.

IaS 1.2 we can never be sure that a measurement tells us the true value of the quantity being measured

IaS 1.3 if we make several measurements of any quantity, these are likely to vary

IaS 1.4 the mean of several repeat measurements is a good estimate of the true value of the quantity being

measured


value probably lies




Literacy focus: Following instructions and describing patterns.

Numeracy focus: Carrying out calculations using experimental data, including finding the mean and the range;

plotting, drawing and interpreting graphs and charts from students’ own and secondary data; using an equation for

calculating the rate of a reaction.

ICT focus: Logging, storing and displaying data in a variety of formats for analysis; using sensors and dataloggers

to monitor the rates of chemical changes.


� understand what is meant by the rate of a chemical reaction

� understand why it is important to control the rates of chemical reactions

� describe methods and interpret results of measuring the rate of chemical reactions.

Key vocabulary

rate of reaction


Most students can appreciate the difference between fast and slow reactions, but can find calculating rates difficult

if they have limited familiarity with graphs – particularly non-linear relationships.


� Ask students to list things that happen quickly and slowly – e.g. drinking a can of coke, fingernails growing – and

ask students to suggest how we can measure some of these – e.g. cm3/s, mm/month.

Learning activities practical c6_09 Low demand � Demonstrate some examples of fast and slow reactions (see the technician sheet). Discuss the

reasons why the chemical industry is interested in rates of reactions (safety, economy). Explain that a rate is the

‘speed’ at which something happens (colloquial but speed is ‘distance covered in a given time’, while rate of

reaction is ‘amount used or produced in a given time’). Discuss what ‘amounts’ could be measured that change

with time. Either demonstrate some of the methods given on the practical sheet or allow students to carry out the

experiments (Standard section below) under supervision.

Teaching and learning notes: Students need to be familiar with units of measurement such as cm3/s or g/s.

c6_09 Measuring rates of reactions continued


Standard demand � Ensure that students understand that different reactions have different rates, and explain the

formula for rate of reaction (Student Book p. 182). Discuss the quantities that can be measured and move into the

three experiments detailed on the practical sheet. If time allows, students should carry out all three methods,

together or in rotation. Note that some of the methods provide opportunities for datalogging. Students should

answer questions1–4 for methods A and B and questions 1–3 for method C. Discuss the reasons why reactions

slow down as they proceed (less and less reactants remain).

Teaching and learning notes: Students will need to plot best-fit line graphs for non-linear data and be able to

discuss the patterns shown by the graphs.

High demand � Having completed the practical work, students should interpret the data through the extension

questions on the practical sheet. Relate the rate of reaction to the gradient of the graphs and explain the difference

between mean rate, mean initial rate and the mean rate between two times. Some students may be able to

calculate an instantaneous rate from the gradient of the tangent to the graph at any point. Discuss the reliability of

data, dealing with outliers, the range and means of the means.

Plenary suggestions Ask students to suggest and discuss the advantages and disadvantages of each method – e.g. mass changes

small so errors caused by balance being jogged or air currents; gas syringes becoming damp and sticking; difficulty

of deciding when the cross has disappeared.

Student Book answers Q1 To make the reactions safe and economic to run.

Q2 One piece of magnesium would dissolve before the other; one would produce gas more quickly.

Q3 2.3 cm3/s

Q4 Put the reactants in a flask on a balance and measure the mass at set times; connect the flask to a gas syringe

and measure the volume of gas produced at set times.

Q5 a) 40 s; b) 80 cm3; c) 80/40 = 2 cm

3/s; d) 8 cm

3/s

e) The point at 15 s does not fit the pattern/is off the line made by the other points.

Practical sheet answers Method A

Q1 Check students have calculated the change in mass from the start and have plotted the graph correctly.

Q2 Steady rising curve; levelling off – students plotting the change in mass against time will have a line rising

steeply; if they have plotted mass against time the line will fall steeply at first.

Q3 At the beginning; there is most reactants at the beginning/the acid is most concentrated at the start/as the

reactants are used up the reaction slows down.

Q4 Points that do not fit on a smooth curve are outliers – students must decide whether to draw a best-fit line

through or close to each point; they can choose to ignore outliers if they can quote sources of error.

Extension

Q5 Check student’s answers.

Method B

Q1 Check that data is plotted accurately; each set of results should be plotted on the same axes (in different

colours).

Q2 Rising curve; levelling off

Q3/4 As in method A

Extension

Q5 As Q5 in method A

Q6 Check the ranges and means calculated. Possible sources of error – time taken to fit bung in flask; variation in

volume and concentration of acid; magnesium ribbon not completely immersed; syringe sticking or not zeroed.

Method C

Q1 Check student’s calculations.

Q2 Check the student’s calculations. Unless one of three results is very different it is difficult to justify ignoring an

outlier.

Q3 The bigger the range, the more uncertainty there is in the mean; judgement of when the cross is invisible is

subjective and differs between observers; hence, there is considerable error.




P Methods for measuring rates of reactions

Objectives


� collect and interpret data on rates of reaction using various methods.

The hydrochloric acid used is CORROSIVE. Wear goggles and report all spillages. Magnesium is FLAMMABLE. Method C gives off a small amount of TOXIC sulfur dioxide gas. Do not put your nose near the boiling tube.


Method A: conical flask • cotton wool • 100 cm3 measuring cylinder • balance

• hydrochloric acid • calcium carbonate chips • stopclock or data logging equipment

Method B: conical flask with bung and delivery tube • gas syringe • clamp stand

• 100 cm3 measuring cylinder • stopclock • hydrochloric acid • magnesium ribbon

Method C: boiling tube • 2 × 10 cm3 measuring cylinders • stopclock

• sodium thiosulfate solution • hydrochloric acid solution

Method A – Measuring changing mass

1 Measure out 50 cm3 of hydrochloric acid and pour it into a conical flask.

2 Weigh out about 1 g of calcium carbonate chips.

3 Add the calcium carbonate to the conical flask swirl it around and place it on a balance. Push a wad of cotton wool loosely in the neck of the flask.

Optional: connect the balance to a data logger and set it to record the mass at intervals of about 0.5 seconds for about 10 minutes.

4 Either record the reading on the balance and start the stopclock, or start the data logger.

5 Record the reading on the balance every 30 seconds for about 10 minutes.

6 Wash and dry the conical flask.



Method B – Measuring changing volume

1 Measure out 50 cm3 of hydrochloric acid and pour it into a conical flask.

2 Cut a piece of magnesium ribbon 4 cm long – fold it loosely.

3 Clamp the gas syringe horizontally, but make sure that the piston can still move easily. Push the piston in to the zero mark.

4 Drop the magnesium ribbon into the conical flask, fit the bung linking it to the gas syringe and start the stopclock.

5 Swirl the flask constantly and record the volume of gas in the syringe every 30 seconds until it either reaches the end of the scale or stops moving.

6 Wash and dry the conical flask and repeat the measurement.

Method C: Monitoring changes in appearance

1 Mark a bold cross on the side of a boiling tube close to the bottom.

2 Measure out 10 cm3 of hydrochloric acid and pour it into the boiling tube.

3 Measure out 10 cm3 of sodium thiosulfate solution in a different measuring cylinder.

4 Pour the sodium thiosulfate solution into the boiling tube, and start the stopclock.

5 Shake the boiling tube gently and look at the cross through the solution.

6 Stop the stopclock when you can no longer see the cross.

7 Wash and dry the boiling tube and repeat the whole procedure.

Results

Record your data for each method in a suitable table.



Questions

Method A

1 Either: calculate the change in mass, from the moment you started timing for each of your readings. Plot a graph of change of mass (y-axis) against time (x-axis); or print a copy of the graph produced by the datalogger.

2 Describe the pattern shown by your graph.

3 When was the rate of reaction biggest? Explain your answer.

4 Are there any outliers in your results? How can you tell?

Extension

5 Calculate: a) the mean rate for the whole reaction

b) the mean rate of reaction in the first minute.

Method B

1 Plot a graph of volume of gas (y-axis) against time (x-axis). If you have two or more sets of results, plot them on the same axes.

2 Describe the pattern shown by your graph.

3 When was the rate of reaction biggest? Explain your answer.

4 Are there any outliers in your results? How can you tell?

Extension

5 Calculate for each set of results: a) the mean rate for the whole reaction

b) the mean rate of reaction in the first minute.

6 Compare your answers to question 11 for each set of results. a) What is the range of the mean rate for the whole reaction and in the first minute?

b) Suggest reasons for the any differences in the sets of results.

Method C

1 Calculate the mean initial rate of the reaction for each of your results using the formula:

11mean initial rate = s

time for cross to disapper

−

What are the range and mean of your mean initial rates?

2 How confident are you that your initial rate is close to the true value? Explain your answer.




Technician sheet


Demonstration:

� Fast reactions – e.g. lighting a match, hydrogen gas burning (hydrogen generator and gas jar), thermite reaction, aluminium/iodine (see c6_07)

� Slow reactions – e.g. rusting (iron wool, nail), magnesium in water, iodine clock (if a member, see CLEAPSS guide)

Practical:


Method A:

� conical flask

� cotton wool



� about 1 g calcium carbonate (medium chips)

� stopclock

� balance

� datalogger (optional)

Method B:

� conical flask with bung and delivery tube

� gas syringe

� clamp stand


� stopclock


� three 4 cm lengths of magnesium ribbon

Method C:

� conical flask

� 2 × 10 cm3 measuring cylinders

� stopclock

� 50 cm3 sodium thiosulfate (0.1 mol dm−3)


� access to thick black waterproof pen

Method

Full instructions for the student activities are given on practical sheet c6_09.



Notes

� The practical sheet describes three separate experiments. These can be done by the whole class in sequence, or as a circus of experiments where groups of students rotate from one experiment to the next. Alternatively the class can do just one of the methods and the others can be demonstrated.

� 20 minutes should be sufficient time to set up and complete each of the three experiments. There should be time for students to do two or three runs using Method B and Method C, while doing one run of Method A.

� Method A provides an opportunity for using datalogging equipment if the balances can be linked to a datalogger.

� Method C can also be carried out as a datalogging exercise using a light sensor in place of the cross and a source of light shining through the boiling tube. The sensor will need to be shielded from extraneous light. The datalogger should show the fall in intensity of transmitted light with time as the reaction mixture becomes more cloudy. The intensity of the light transmitted is proportional to the amount of sulfur precipitated in the reaction.

Health and Safety

� The hydrochloric acid used is CORROSIVE. Students should wear goggles and report all spillages.


� Method C gives off TOXIC sulfur dioxide gas. The quantity given off is very small and the risk is low, but make sure the ventilation is good.



c6_10 Changing rates of reactions

Resources

Student Book pages 184−185 � Interactive Book: Naked Scientist animation ‘What controls the rate of a chemical reaction?’ � Homework pack c6_10

Files on Teacher Pack CD: c6_09_practical; c6_10_practical; c6_10_technician

Equipment for practical(s)

Learning outcomes C6. 2.17 understand how reaction rates vary with the size of solid particles the concentration of solutions of

chemicals and the temperature of the reaction mixture; a qualitative treatment only is expected

C6. 2.20 use simple ideas about collisions to explain how chemical reactions take place

C6.2.21 use simple collision theory and ideas about collision frequency to explain how rates of reaction depend on

the size of solid particles and on the concentration of solutions of dissolved chemicals; the effect of temperature on

collision frequency is not considered since activation energy has a greater influence

Ideas about Science IaS 2.1 it is often useful to think about processes in terms of factors which may affect an outcome (or input

variables which may affect an outcome variable)

IaS 2.2 to investigate the relationship between a factor and an outcome, it is important to control all the other

factors which we think might affect the outcome (a so-called ‘fair test’)

IaS 2.3 if an outcome occurs when a specific factor is present, but does not when it is absent, or if an outcome

variable increases (or decreases) steadily as an input variable increases, we say that there is a correlation between

the two

IaS 2.6 to investigate a claim that a factor increases the chance (or probability) of an outcome, scientists compare

samples (e.g. groups of people) that are matched on as many other factors as possible, or are chosen randomly so

that other factors are equally likely in both samples. The larger the samples, the more confident we can be about

any conclusions drawn

IaS 2.7 even when there is evidence that a factor is correlated with an outcome, scientists are unlikely to

accept that it is a cause of the outcome, unless they can think of a plausible mechanism linking the two

Numeracy focus: Plotting, drawing and interpreting graphs and charts; using an equation for calculating the rate of

a reaction; using ideas about correlation in the context of rates of reaction.

ICT focus: Using sensors and dataloggers to monitor rates of chemical changes.


� explain how reactions occur when there are collisions between particles

� understand how changing conditions change the rate of reactions

� explain how changing conditions affect the collisions between particles

Key vocabulary

concentration


The organisation of the practical work can overwhelm the learning of the effects of changing factors on rates of

reaction and the explanations. It is important to find time for discussion of the ideas as well as collection of data.


� Demonstrate the cornflour fireball or explosion (see the technician sheet). Ask students to explain why the

reaction was so fast when the powder was blown into the flame.

Learning activities practical c6_09 + practical c6_10 Low demand � Remind students that reactions take place when some gases mix, when some liquids mix and

when some solids mix with gases and liquids. Ask students to explain what they think is happening to the particles

of the reactants during a reaction. Draw out the ideas of the collision theory and, hence, that the more collisions

there are per second, the faster the reaction. At this point introduce the activity on practical sheet c6_10. For a

group of lower-attaining students it may be sensible to carry out one investigation and give groups of students

tasks to collect specific data that can then be pooled to work towards a conclusion. Discuss the requirements for a

fair test and the confidence in the correlations observed. Relate the conclusion to the collision theory model.

c6_10 Changing rates of reactions continued


Standard demand � Having discussed the concept of collision theory, introduce the investigation. Ask students to

suggest factors that could affect the rate of reaction. Select one or all of particle size, concentration and

temperature. Either divide the class into small groups or into three teams to carry out one or all of the

investigations. Students will need practical sheet c6_09 for the methods for measuring rate. Practical sheet c6_10

gives instructions for varying one factor in each of the three methods given. However, before handing out the

sheet, students should be asked to make predictions about how they think the factor will affect the rate, how the

factor can be varied while other factors are controlled, and what data need to be collected. In each investigation the

initial rate is measured so there is no need to wait for a reaction to be completed – this saves a lot of time. See the

technician sheet for ways of organising this activity. Having collected shared data, students can then think of the

most appropriate way of displaying results to show the patterns and possible correlations. They should consider if

they have enough data to be confident about the correlation they (may have) discovered and compare their

conclusions with their predictions.

High demand � Students should use the collision theory to provide an explanation for the correlations observed in

each of the investigations, and discuss whether or not it shows that the correlation represents a causal link

between the factor and the rate of reaction. Students should discuss the limitations of their data.

Plenary suggestions As a whole class, draw up a summary of the conclusions to the investigations showing the link between factors and

rates and the explanations for each. Individual students or groups could contribute separate parts of the summary.

Student Book answers Q1 More frequent

Q2 Particles cannot move freely in solids; so they are much less likely to collide.

Q3 To find if there is a correlation between any factor and the rate of reaction; only that factor can be changed.

Q4 Make the pieces of zinc smaller; warm the acid; use more concentrated acid; all increase the likelihood of

collisions.

Q5 The grain dust particles are very small so have a large surface area; there is a high frequency of collisions with

air particles; so combustion is very fast.

Q6 If the stain remover is used straight from the bottle it will be more concentrated; there will be a higher frequency

of collisions with the stain particles; so the stain will be removed more quickly.

Practical sheet answers Investigation A:

Q1 Check students’ means and ranges.

Q2 Only a bar chart is appropriate for the three different-sized particles of calcium carbonate.

Q3 The smaller the particles the faster the rate; the correlation should be clear although the relationship is unclear.

Q4 Not very confident; use more different sizes, use graded particle sizes, look at different reactions.

Q5 Increasing surface area increases the number of collisions.

Investigation B:


Q2 Best-fit line graph of initial rate against; straight line or curve.

Q3 The higher the concentration the greater the rate.

Q4 Quite confident; improve method to reduce errors; do more repeats; use more concentrations; look at different

reactions.

Q5 Increasing concentration means more particles in a certain volume; so more chance of collisions.

Investigation C:


Q2 Best-fit line graph of initial rate against temperature; smooth curve.

Q3 The higher the temperature the greater the rate.

Q4 Quite confident; use a thermostatically controlled water bath; use a different method (e.g. method B); do more

repeats; use a wider range of temperature; look at different reactions.



c6_10 Changing rates of reactions

P Investigating factors that change the rate of reactions

Objectives


� collect data to investigate the effect of changing one of a number of factors that may affect the rate of a reaction.

Hydrochloric acid is CORROSIVE. Wear goggles and report all spillages. Magnesium is FLAMMABLE. The reaction in investigation C gives off TOXIC sulfur dioxide. Do not put your nose close to the boiling tubes.


Investigation A: conical flask • cotton wool • 100 cm3 measuring cylinder

• balance • stopclock or datalogger • hydrochloric acid

• calcium carbonate (large chips, small chips and powder)

Investigation B: conical flask with bung and delivery tube • gas syringe • clamp stand

•100 cm3 measuring cylinder • stopclock • hydrochloric acid

• magnesium ribbon • distilled water

Investigation C: large beaker • 2 boiling tubes • 2 measuring cylinders (10 cm3)

• 2 thermometers • stopclock • sodium thiosulfate solution

• hydrochloric acid solution • source of hot water (and ice)

Method

Investigation A: Particle size

Use method A from practical sheet c6_09 to measure the initial rate of reaction of hydrochloric acid with calcium carbonate of different sized particles – large chips, small chips and powder.

1 Carry out the experiment with three different sizes of calcium carbonate. Make sure you use the same mass of calcium carbonate for each measurement.

2 Record the mass every 30 seconds for about 2 minutes.

Investigation B: Concentration

Use method B from practical sheet c6_09 to measure the initial rate of reaction of magnesium with hydrochloric acid of different concentrations.

1 Carry out the experiment with the quantities of reactants shown in the table below. Put the water and hydrochloric acid in the conical flask first.

Magnesium ribbon length

(cm)

Hydrochloric acid volume (cm3)

Distilled water volume (cm3)

Concentration compared to hydrochloric acid (%)

4 50 0 100

4 40 10 80

4 30 20 60

4 20 30 40

4 10 40 20

c6_10 Changing rates of reactions continued


2 Record the volume of gas collected every 30 seconds (or more frequently if you can) for 2 minutes or until the reaction stops, whichever comes first.

3 Repeat the reading for each mixture of acid and water.

Investigation C: Temperature

Use method C from practical sheet c6_09 to measure the initial rate of reaction of sodium thiosulfate solution with hydrochloric acid at different temperatures. Mix hot and cold water in a large beaker to get the range of temperatures you need.

1 Measure the sodium thiosulfate and hydrochloric acid solutions into separate boiling tubes and stand both tubes in the beaker of water at the desired temperature.

2 Measure and record the temperature of each solution – use separate thermometers to avoid contaminating the solutions. Then pour the solution from one boiling tube into the one with the cross marked on it and start the stopclock. Time how long it takes for the cross to disappear.

3 Repeat the measurement for each of these temperatures (°C): 10, 20, 30, 40, 50, 60 and 70.

Results

Record the data from your investigation in a suitable table.

Questions

1 For each investigation, find the initial rate on each run. Calculate the range and mean for each run where the conditions were the same.

2 Draw a suitable chart for the factor that was changing in your investigation against the initial rate.

3 Describe the pattern shown in your chart. Does it show a correlation between the initial rate of the reaction and the factor that you changed?

4 How confident are you that your conclusion is correct? How could you increase your confidence?

5 How can you explain the correlation that you have found? (Investigations A and B only.)

6 Share data and conclusions for all three investigations and write a summary of the effect of changing the three factors on the rate of chemical reactions and the mechanisms explaining them.



c6_10 Changing rates of reaction

Technician sheet


Demonstration

� Bunsen burner

� cornflour, custard powder or milk powder (all the powders must be dry)

� spatula

Practical


Investigation A:

� conical flask and cotton wool


� balance

� stopclock or datalogger


� calcium carbonate – large chips, small chips and powder

Investigation B:

� conical flask with bung and delivery tube

� gas syringe

� clamp stand


� stopclock


� 50 cm of magnesium ribbon

� distilled water

Investigation C:

� large beaker

� 2 × boiling tubes

� 2 × measuring cylinders (10 cm3)

� 2 × thermometers

� stopclock

� 100 cm3 sodium thiosulfate solution (0.1 mol dm−3)

� 100 cm3 hydrochloric acid solution (1 mol dm−3)

� access to a source of hot water and ice

Method

Full instructions for the student practicals are given on practical sheets c6_10 and c6_09.

Demonstration

1 Stand a Bunsen burner on a large bench mat or metal tray and light the burner.

2 Put some of the powder on a spatula and hold it in the flame. It should ignite and burn steadily.

c6_10 Changing rates of reaction continued


3 Next hold a spatula of the powder a metre or so above the Bunsen flame. Tap the spatula to spill some of the powder into the flame. It should produce a dramatic fireball as the powder ignites.

4 See the internet for instructions, using the search term ‘custard powder explosion’, using a tin can with a lid.

Notes

� There are a number of ways of organising this activity.

– Each of the investigations can be carried out by the whole class in sequence. This will need about 3 hours altogether for data collection.

– Alternatively, groups of two or three students can do just one investigation, with results being pooled. This will take over an hour for data collection.

– The quickest method is for the class to be divided into three teams with each team working on one of the investigations. This should require less than an hour for data collection. All the results and conclusions can be pooled at the end.

– Lessons c6_09 and c6_10 can be linked together, so that students carry out the investigations at the same time as learning the techniques for measuring rate of reactions.

– Finally, just one of the investigations can be carried out by the whole class. This should take about 30 minutes for data collection. Data for the other investigations can be sought from other sources.

� Calculation of initial rates: Low and Standard demand

– Investigation A – initial rate is the change in mass in the first 30 seconds or 1 minute; units are g/s

– Investigation B – initial rate is the volume of gas collected in the first 30 seconds or 1 minute; units are cm3/s.

– Investigation C – initial rate = 1 ÷ time taken for cross to disappear; units are s−1.

High demand

– Investigations A and B – students should plot a graph of the change of mass or volume of gas against time, and measure the gradient of the tangent to the graph at time = 0.

– Investigation C – initial rate = 1 ÷ time taken for cross to disappear; units are s−1.

� Investigation A – the rate with the largest marble chips may be very slow indeed, while with powder the reaction could be complete within 30 seconds.

� Investigation B – it is suggested that concentration is given as ‘% of the hydrochloric acid solution’ rather than as g/dm3 or mol/dm3. Alternatively, the dilution (i.e. % water) could be used. There is a constant error due to the time taken to fit the bung. Students could be asked to devise a way of avoiding this error (e.g. by holding the magnesium ribbon on a thread which is released with the bung almost in place). The gas syringe may become damp and sticky after repeated measurements.

� Investigation C – if a large beaker is used for the water bath there will be little temperature change during the reaction. The temperature at the start and end of the run could be measured and the mean taken. It is not necessary to get the temperatures exactly to 30 or 40 °C, etc. so long as a reasonable range of temperatures is used.

Health and Safety

� The hydrochloric acid used is CORROSIVE. Students should wear goggles and report all spillages.


� Investigation C gives off TOXIC sulfur dioxide gas. The quantity is very small and the risk is low, but make sure the ventilation is good.



c6_11 Catalysts

Resources



Equipment for practical(s)

Learning outcomes C6.2.18 understand that catalysts speed up chemical reactions while not being used up in the reaction

C6.2.19 interpret information about the control of rates of reaction in chemical synthesis


reactions) including d. carrying out the reaction in the right conditions (such as temperature

Ideas about Science IaS 2.1 it is often useful to think about processes in terms of factors which may affect an outcome (or input

variables which may affect an outcome variable)

IaS 2.2 to investigate the relationship between a factor and an outcome, it is important to control all the other

factors which we think might affect the outcome (a so-called ‘fair test’)

IaS 2.3 if an outcome occurs when a specific factor is present, but does not when it is absent, or if an outcome

variable increases (or decreases) steadily as an input variable increases, we say that there is a correlation between

the two

Literacy focus: Describing the activity of catalysts.

Numeracy focus: Plotting, drawing and interpreting graphs and charts from students’ own and secondary data;

using an equation for calculating the rate of a reaction.

ICT focus: Viewing video clips to illustrate the manufacture of chemicals on a large scale in industry; using sensors

and dataloggers to follow rates of chemical changes.


� understand how catalysts can speed up reactions

� interpret information about controlling rates of reaction

Key vocabulary

catalyst �� catalytic converter


Students may think that a catalyst, such as the platinum in a catalytic converter, is just a convenient place for the

reaction to occur and not understand that the atoms of the catalyst are actively involved in the reaction.


� Ask students to list ways of making a reaction used in the chemical industry go faster (higher temperature, higher

pressure/concentration, smaller particles) and suggest reasons why there are limits to these (cost).

Learning activities worksheet c6_11 + practical c6_11 Low demand � See if students can recall the role of the catalyst in the catalytic converter fitted in cars (covered in

module C1, lesson c1_12). Draw out the idea that catalysts make reactions go faster and can be used over and

over again. Students could research other examples of industrial catalysts. Introduce the decomposition of

hydrogen peroxide (a source of oxygen – hydrogen peroxide is used as a bleach in household cleaners and hair

colouring) as a slow reaction and discuss how students could investigate which substances are catalysts for the

reaction. Students can then carry out part 1 of the practical work. There are further questions on the worksheet.

Teaching and learning notes: Students need to understand that catalysts don’t make reactions happen that

wouldn’t happen any other way – they speed them up.

Standard demand � Discuss the role of catalysts in industry and consider the characteristics of catalysts – they

affect the rate of reactions, they take part in the reaction but are left at the end to be used again, a small amount of

a catalyst can have a big effect; the amount and particle size of a catalyst. Introduce the activity to investigate the

catalysts for the decomposition of hydrogen peroxide (see above). The two parts of the activity are separate and

there is no need for any or all of the students to do both. Students should discuss and perhaps draw diagrams

suggesting a mechanism for the action of (heterogeneous) catalysts. There are further tasks on the worksheet.

c6_11 Catalysts continued


Teaching and learning notes: The reduction of activation energy in a catalysed reaction is not covered here.

High demand � Students should consider the role of chemical engineers in deciding the optimum conditions for an

industrial process in the light of what they have learned about rates of reaction. As well as considering the effect of

particle size, concentration, temperature and catalysts on the rate, they should also consider safety, environmental

and economic factors. The worksheet includes some scenarios for students to investigate.

Plenary suggestions Divide the class into teams (of 4–6) and challenge each team to devise three questions (and answers) on all

aspects of rates of reaction to put to the other teams within the time available.

Student Book answers Q1 Some reactions are very slow.

Q2 The catalyst can be used over and over again.

Q3 a) Zinc oxide; copper oxide; manganese dioxide

b) Suggests that copper oxide powder is the best; it produced the most oxygen in the same time.

c) They should have tested manganese dioxide powder and copper oxide lumps; measurements should be repeated; other substances should be tested.

Q4 a) Mass of zinc used; volume of acid b) Temperature (hot acid) c) Zinc powder; with hot; concentrated; acid; and copper catalyst d) Zinc powder; with dilute acid; and copper catalyst; concentrated acid is corrosive; heating is expensive.


Q1 A; C B: Catalysts are not used up in reactions. D: The catalysts used to clean up pollutants in cars are rare metals. E: Many substances are used as catalysts in the chemical industry.

Q2 Making ammonia by the Haber Process with iron Catalytic converters in cars with platinum/rhodium Turning vegetable oils into margarine with nickel Manufacture of ethanoic acid with rhodium/iridium


Q1 a) The time taken for the indicator to change colour will be shorter with the catalyst. b) All the other factors must be kept constant; temperature, concentration of reactants, particle size, amounts. c) Lee is correct; unless Kim can suggest a mechanism for how the catalyst works.

Q2 Should cover all the methods used to measure rates, formulae and graphical methods for determining rates, the

effect of each factor on the rate of reaction and collision theory as a mechanism.


Q1 Engineers want the reactants to spend as little time in the reaction vessel as possible; so that it can be

relatively small; and more product can be made more economically.

Q2 The conditions used are vanadium oxide catalyst; temperature 400–500 °C; around normal pressure. Students

should justify their choices.

Practical sheet answers Q1 Manganese dioxide should be observed to be the most effective catalyst; with copper oxide and iron oxide

showing some activity.

Q2 This experiment shows that manganese dioxide is the best of the four substances tested; many more

substances must be tested before a more general conclusion can be stated.

Q3 Check student’s calculations.

Q4 Students should draw a best-fit line graph; check the axes and points on the graph.

Q5 Straight line or curve shows that the rate increases with the mass of catalyst.

Q6 The more catalyst powder used, the greater the surface area exposed to the reactants; so more collisions can

take place between reactant particles and the catalyst; increasing the chance of reaction.



c6_11 Catalysts

P What effect does a catalyst have on a rate of reaction?

Objectives

Hydrogen peroxide decomposes to water and oxygen. The reaction is usually slow. In this activity you will:

� collect and interpret data on the effect of a catalyst on the rate of reaction.

Hydrogen peroxide solution and the powders used in this experiment are IRRITANTS. Avoid touching them and clear up all spillages. Wear goggles.


4 × boiling tubes • spatula • conical flask with bung • connector to gas syringe • measuring cylinder

• clamp and stand • wood splint • Bunsen burner • hydrogen peroxide solution • copper oxide • iron oxide

• manganese dioxide • zinc oxide

Method

Part 1: Which substances are catalysts?

1 Measure 5 cm3 of hydrogen peroxide solution into each of the boiling tubes.

2 Getting a little powder on the end of a spatula, add copper oxide to the first boiling tube, iron oxide to the second, manganese dioxide to the third and zinc oxide to the last.

3 You can test for oxygen by holding a glowing splint in the top of each boiling tube when you see a reaction taking place.

4 Record your observations.

Part 2: Does the amount of catalyst affect the rate of the reaction?

1 Clamp the gas syringe horizontally in the stand, and make sure the piston moves freely.

2 Measure out 20 cm3 of hydrogen peroxide solution into the conical flask.

3 Weight out 0.25 g of the best catalyst from part 1.

4 Add the catalyst to the conical flask, fit the bung, start the stopwatch and swirl the flask.

5 Read the volume of gas collected in 20 seconds.

6 Wash the conical flask, and return the gas syringe to 0.

7 Repeat the experiment with different amounts of catalyst – e.g. 0.5 g, 0.75 g, 1.00 g.

Results

Record your results in a suitable table.

Questions

1 From part 1, which was the best of the four materials as a catalyst for this reaction?

2 Is the substance in your answer to question 1 the best catalyst for the decomposition of hydrogen peroxide? Explain your answer.

3 Calculate the initial rate of reaction in part 2 for each mass of catalyst:

3volume of gas collectedinitial rate cm /s

20 =

4 Plot a graph of initial rate (y-axis) against mass of catalyst (x-axis).

5 What pattern does your graph show? Is it evidence for a correlation?

6 What mechanism can you suggest for the correlation?



c6_11 Catalysts

1 What are catalysts?

1 Which of the following statements about catalysts are true? Correct the statements that are false.

A A catalyst makes a reaction go faster.

B Catalysts are used up in reactions.

C Catalysts can be used over and over again in reactions.

D The catalysts used to clean up pollutants in cars are common metals.

E Very few substances are used as catalysts in the chemical industry.

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2 Use the internet to match up the following industrial processes and the catalysts they use:

Process Catalyst

Making ammonia by the Haber process nickel

Catalytic converters in cars rhodium/iridium

Turning vegetable oils into margarine iron

Manufacture of ethanoic acid platinum/rhodium

2 Investigating catalysts

1 Kim and Lee are investigating if substance X will act as a catalyst in the reaction between two reactants, A and B. When A and B react they form an acid, which will change the colour of an indicator.

a) How will Kim and Lee know if X is a catalyst for the reaction of A with B?

b) What must Kim and Lee do to be sure that it is the catalyst X that causes the effect?

c) When Kim and Lee do their investigation it does seem that when X is added to the mixture the reaction is faster.

Kim says, ‘It shows that X is the cause of the reaction rate increasing.’

Lee replies, ‘No – it just shows that there is a correlation between X and the rate of reaction.’

Who is correct? Explain your answer.

c6_11 Catalysts continued


2 Draw a memory map for this ‘rate of reaction’ topic – a start is suggested below.

3 Controlling rates of reaction

1 Explain why it is a chemical engineer’s aim to make a chemical process go as fast as possible without causing an explosion.

2 The raw materials for making sulfuric acid are sulfur, air and water. The difficult stage in the process is reacting sulfur dioxide, SO2, with oxygen, O2, to make sulfur trioxide, SO3:

2SO2(g) + O2(g) → 2SO3(g)

The reaction is very slow under normal conditions.

Use the following information to decide what conditions could be used to get a good yield of sulfur trioxide economically and safely. Write a report explaining your decisions.

Rate of reaction

Increasing the temperature increases the rate of reaction.

Above about 400 °C the reaction begins to produce sufficient yield to be useful.

High pressure reaction vessels are very

expensive and there is increased risk of leaks.

The cost of fuel increases with temperature. Above about

500 °C special alloys are needed for the reaction vessels.

Increasing the concentration of oxygen by using pure oxygen instead of air

increases the rate of reaction.

Pure oxygen is a hazard as it can make fires burn more fiercely.

Increasing the pressure on the gases would increase the rate of reaction.

An oxide of vanadium acts as an effective

catalyst for the reaction.

Vanadium compounds are expensive.

It is expensive to separate oxygen from air.

Methods for investigating rates

Factors that affect rates

Calculating rate of reaction



c6_11 Catalysts

Technician sheet



� 4 boiling tubes

� conical flask with bung and connector

� gas syringe


� clamp and stand

� wood splints

� Bunsen burner

� 100 cm3 of hydrogen peroxide solution (20 vol.)

� spatula

� powders, about 2 g each, of:

– copper oxide

– iron(III) oxide

– manganese dioxide

– zinc oxide.

Method

Full instructions for the experiment are given on practical sheet c6_11.

Notes

� The two parts of the activity can stand alone.

� If part 2 is being done without part 1, then use manganese dioxide as the catalyst.

Health and Safety

� Hydrogen peroxide solution is an IRRITANT. The four substances suggested as possible catalysts are also HARMFUL. Students should wear goggles and they may like to have disposable gloves to avoid contact with the materials. Clear up all spillages.



c6_12 Synthesising a product

Resources


Files on Teacher Pack CD: c6_12 worksheet, c6_12_technician

Equipment for practicals

Learning outcomes C6. 2.1 identify the stages in a given chemical synthesis of an inorganic compound (limited to acid–alkali

reactions), including: a. choosing the reaction or series of reactions to make the required product

b. carrying out a risk assessment, c. working out the quantities of reactants to use, d. carrying out the reaction

in suitable apparatus in the right conditions (such as temperature, concentration), e. separating the product from

the reaction mixture (limited to filtration), f. purifying the product (limited to evaporation, crystallisation and drying in

an oven or desiccator), g. measuring the yield and checking the purity of the product (by titration)

Ideas about Science See previous lesson plans.

Literacy focus: Writing a report or preparing presentation.

Numeracy focus: Reinforcement of techniques used earlier in the module.

ICT focus: Using a variety of techniques to make presentations and prepare reports.


� Apply our understanding of acid–alkali reactions and factors affecting rates of reaction to the synthesis of a new

chemical product

Obstacles to learning This lesson is largely a summary of the unit. Students may find that calling on all their learning to carry out the task

is a struggle.


� This lesson is an opportunity to draw all the concepts covered in this module together – neutralisation, energy

changes, rates of reaction and calculating reaction masses. This is done through the stages of the synthesis of a

compound, which were introduced in the first lesson of the module and referred to subsequently. Start the lesson

by stating that students will plan a process to manufacture Epsom salts (magnesium sulfate) or some other

inorganic compound. Students should work in groups and start by making a list of the questions they need

answers to in order to carry out the task. The worksheet gives students a series of questions they will need to

answer in the process.

Learning activities worksheet c6_12 Low demand � The first and most important stage is to decide on the raw materials and the reaction to be used.

Tell students that magnesium sulfate (or whichever example is being used) is a salt. Groups should then research

the reactions that could be used to produce the target material and make a choice of which they think is best. The

Student Book makes one suggestion (p. 188) but this does not have to be the reaction chosen. Students could plan

their chosen reaction in the laboratory doing a risk assessment and, with the teacher’s approval and supervision,

carry it out (technician sheet). Students should write a report on their work or prepare a presentation.

Teaching and learning notes: Students need to know the reactions of acids and how to decide when a reaction is

complete.

Standard demand � Having chosen an appropriate reaction to use, each group should go on to decide the

conditions required to get a product quickly (considering risks and cost), the effect of any energy released, and how

to separate and purify their product using information provided (e.g. in making Epsom salts, the reaction is

exothermic, magnesium carbonate is an insoluble solid, concentrated sulfuric acid is highly corrosive) or

information found by research. Students can carry out some test reactions under supervision (see worksheet).

Students should write a report on their work or prepare a presentation.

Teaching and learning notes: Students will need to understand energy changes in reactions, factors that affect

rates and methods of separating substances.

c6_12 Synthesising a product continued


High demand � Alongside the work suggested above, groups will also need to calculate the amount of reactants

required to produce an appropriate yield of the product (say 1 g of magnesium sulfate). They also need to plan how

to measure their actual product yield and suggest ways of testing its purity. If time allows, students could do a trial

(small-scale) preparation. Students should write a report on their work or prepare a presentation.

Plenary suggestions Students present their reports on their suggestions for the process, and question each other’s decisions.

Student Book answers Q1 Magnesium carbonate + sulfuric acid → magnesium sulfate + water + carbon dioxide

Q2 Wear goggles; protective clothing; avoid spills; keep away from reactive metals.

Q3 Reaction is exothermic.

Q4 Increase the surface area/decrease particle size of the magnesium carbonate; raise the temperature of the

reactants; use more concentrated sulfuric acid.

Q5 Solid impurities filtered off; solution heated to evaporate water; and crystallise magnesium sulfate; crystals are

filtered and dried.

Q6 168 tonnes

Q7 90%

Q8 a) 4.5 cm3; b) About 10% of the sulfuric acid is unreacted.

Worksheet answers Answers to the questions on the worksheet depend on the target salt chosen for the class or by each group. Below

are some suggestions as to what to look for in answers or in the reports produced.

Activity 1 (Low demand)

Q1 & 2 The technician sheet suggests some salts and possible raw materials. A reaction that produces a gas gives

a good indication of when a reaction is complete. Reactions involving solutions of reactants must be titrated.

Q3 Check student’s word equation.

Q4 Use the CLEAPSS Hazcards to check hazards. Risks can be reduced by using less concentrated acid, by using

alternatives to toxic substances, and by taking precautions – wear goggles, lab coat, gloves, do the experiment

in a fume cupboard, etc.


Q1 Most reactions with strong acids are exothermic. Students can test by mixing the reactants in a test tube and

feeling the temperature change.

Q2 Excess heat from a reaction should be removed by a ‘heat exchanger’ – cold water bath.

Q3 Increased temperature (up to about 60 °C in the lab); more concentrated acid (up to 1 mol dm−3

); powdered solid

reactants are permitted conditions. No catalyst is needed for acid/base reactions; a little copper sulfate solution

added to zinc makes the metal react faster with acids.

Q4 Check student’s quantities as well as method before giving approval.

Q5 Limited to filtration, evaporation and crystallisation. Note that many salts are hygroscopic and difficult to

crystallise; nitrates generally decompose on heating; as do transition metal sulfates.


Q1 Check the formulae; balancing; and state symbols.

Q2 a) Using MgCO3 and 1 M H2SO4 it is 0.7 g and 0.82 g (8.3 cm3), respectively – but solid should be in excess.

b) Using the same reactants, the amounts are 7 tonnes and 8.2 tonnes (833 333 dm3).

100 cm3 of the respective 1 mol dm

−3 solutions contain 9.8 g of sulfuric acid and 3.65 g of hydrochloric acid.

Students will need to weigh out sufficient solid to be in excess of the amount of acid they choose.

Q3 e.g. Appearance, test pH, dissolve and titrate against standard alkali, recrystallise and collect impurities.

Q4 Check student’s calculations of theoretical and actual yield.




Technician sheet



� test tubes and test tube rack

� thermometer

� measuring cylinders (10 cm3 and 100 cm3)

� conical flask with attachment to gas syringe

� stopclock

� large beakers

� filter funnel

� filter paper


� Bunsen burner

� tripod and gauze.

� access to balance

� source of hot water

� indicators and reactants mentioned in the table below

Method

Students will be devising their own procedures – which will be checked and approved by the teacher or technician.

Notes

� The table on the next sheet gives suggested products and their possible raw materials. Each group of students could be given a different product, or the groups could be in ‘competition’ to produce the best process for a single product.

Health and Safety

� Students should find out if any of the substances they intend to use are hazardous. Teachers/technicians should check their findings before approving a procedure.

� Students should wear goggles and a lab coat. They should report all spillages.

� if a member, refer to CLEAPSS Hazcards.



Product RFM Suggested raw materials Comments

Epsom salts

(magnesium

sulfate, MgSO4)

120 sulfuric acid +

magnesium carbonate

� use 1 mol dm−3

acid or lower

� magnesium sulfate is hygroscopic

but can be heated to dryness sulfuric acid +

magnesium

sulfuric acid +

magnesium oxide

copper sulfate

(CuSO4)

159.5 sulfuric acid +

copper oxide


acid or lower

� copper compounds are toxic

sulfuric acid +

copper carbonate

iron(II) sulfate

(FeSO4)

152 sulfuric acid +

iron


acid or lower

� iron(II) compounds oxidise in the air

slowly sulfuric acid +

iron(II) oxide

sulfuric acid +

iron(II) carbonate

potassium chloride

(KCl)

74.5 hydrochloric acid +

potassium hydroxide


acid or lower

� all potassium compounds are

soluble hydrochloric acid +

potassium carbonate

calcium chloride

(CaCl2)

111 hydrochloric acid +

calcium


acid or lower

� calcium is fairly reactive

� calcium hydroxide is partially

soluble

� calcium chloride is deliquescent but

can be heated to dryness

hydrochloric acid +

calcium hydroxide

hydrochloric acid +

calcium carbonate




‘Saltz’ is a new company that manufactures salts for many different uses. They need your help to plan the synthesis of a particular salt. You will be told the name of the salt, and below are some suggestions about what you need to do.

1 Choosing the reaction

Name of salt: ....................................................................

1 Research the reactions that could be used to make your salt.

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2 Choose the raw materials that you will use, and explain why you have chosen them.

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3 Write a word equation for the reaction you have chosen.

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4 What are the hazards of your raw materials or are caused by the reaction? How could you make the risk lower?

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5 Design a presentation or prepare a report describing the work you have done on your product.



2 Making the products

1 Is the reaction you have chosen exothermic or endothermic?

2 How will you cope with the energy changes that happen in the process?

3 What conditions are needed to produce the product as quickly as possible, but safely and economically?

4 You may be able to carry out some tests to find out the answer to the questions above. Plan your experiment and make a list of the apparatus and materials you need. You will only be able to carry out your investigation if your teacher approves your plan.

5 How will you separate your product and purify it?


3 Finding the amounts (Higher tier only)

1 Write a balanced chemical equation for the reaction you are using.

2 Calculate the amount of reactants needed to produce:

a) 1 g of trial product

b) 10 tonnes of manufactured product.

3 Suggest ways of testing the purity of your product.

4 You may be able to carry out a trial preparation of your product if your teacher approves your method. Weigh the sample that you prepare and calculate the percentage yield that you achieved.


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