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EdExcel Triple Science Unit C3EdExcel Triple Science Unit C3

Chemistry in Chemistry in ActionAction

N Smith

St. Aidan’s

21/04/23Topic 1 – Quantitative Topic 1 – Quantitative AnalysisAnalysis

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Chemical EconomicsChemical EconomicsHi. We’re industrial scientists and we want to analyse this

chemical. What tests could we do?

There are two main types of analysis:

1) Qualitative – descriptions of what is present

2) Quantitative – analysis of how much of a chemical is present

You need to use different tests for different ions – for example, if this chemical contains copper chloride

then we’d need to verify by testing for copper ions and

testing for chloride ions.

Tests like these are important for industries like the water

industry and medicine. Why?

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Testing using PrecipitatesTesting using PrecipitatesSome metal compounds form precipitates, i.e. an insoluble solid that is formed when sodium hydroxide is added to them. Consider calcium chloride:

CaCl2 + 2NaOH Ca(OH)2 + 2NaCl

What precipitates are formed with the following metal compounds when they react with sodium hydroxide?

Metal ion Precipitate formed

Soluble or insoluble?

Colour

Calcium Calcium hydroxide White

Aluminium

Copper

Iron(II)

Iron(III)

21/04/23Ammonium, nitrate, bromide and Ammonium, nitrate, bromide and iodide ionsiodide ions

Ammonium ions:

Add sodium hydroxide, warm it and test the gas using damp litmus paper – ammonia gas turns damp litmus paper blue.

Chloride, bromide and iodide ions:

Add a few drops of dilute nitric acid followed by a few drops of silver nitrate solution. A white precipitate should be formed for chloride ions, a pale yellow precipitate should be formed for bromide ions and a darker yellow precipitate for iodide ions.

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Flame tests revisionFlame tests revisionCompounds containing lithium, sodium, potassium, calcium and barium ions can be recognised by burning the compound and observing the colours produced:

Lithium

Red

Sodium

Yellow

Potassium

Lilac

Calcium

Brick red

Barium

Green

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Testing for carbonate ionsTesting for carbonate ions

Limewater turns milky/cloudy

Limewater

Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water

21/04/23Topic 2 – Quantitative Topic 2 – Quantitative AnalysisAnalysis

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WaterWaterAmazing facts about water:

1) 95% of your body mass is water (94% in women due to a higher body fat content)

2) Dinosaurs would have drunk the same water you do

3) Water dissolves more substances than any other liquid – most ionic substances are soluble and most covalent substances are insoluble

4) Around 75% of the world’s surface is made of water

5) To feel thirsty you need to lose around 1% of your body water

6) 5,000 children die every day due to not having clean drinking water

7) An average person in the West uses 200-300 litres of water every day

21/04/23

Hard and Soft WaterHard and Soft WaterDefinition: Hard water is water that contains

lots of dissolved ions like magnesium and calcium that come from contact with rocks.

When it reacts with soap it forms scum.

Advantages of hard water

Disadvantages of hard water

Dissolved ions are good for your health

They also help reduce the development of heart disease

More soap is needed to form lather

Can lead to deposits forming (e.g. limescale) so its more expensive

There are two types of hard water – permanent and temporary. What is the difference between these two?

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Temporary hard waterTemporary hard waterTemporary hard water is water that contains hydrogencarbonate ions (HCO3

-). You can boil this water to soften it up and here’s what happens:

Step 1 – The hydrogencarbonate ions decompose to produce carbonate ions

Step 2 – The carbonate ions react with calcium and magnesium ions to form precipitates

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Measuring Water HardnessMeasuring Water HardnessHardness can be measured by adding soap and seeing how much soap it takes to form a lather:

No. of drops of soap needed to form a lather

Water sample Before boiling After boiling

A 27 27

B 25 4

C 4 4

1) Which sample is soft water?

2) Which sample is temporary hard water?

3) Which sample is permanent hard water?

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Removing hardnessRemoving hardnessOne way to remove permanent hardness:

Pass the water through an “ion-exchange” column that contains a special resin to “swap” the calcium and magnesium ions for sodium or hydrogen ions. This is how some commercial water softeners work.

Ca2+

Na+

ResinCa2+

Na+

Resin

Ca2+

Na+

Resin

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The MoleThe MoleDefinition: A mole is a measure of the number of particles in a substance. 1 mole is 6x1023

particles.Molar Mass (g/mol)

Molar mass is the mass of one mole of a substance and is equal to the relative atomic mass (in grams).

For example:

1)Carbon has a relative atomic mass of 12, so 1mol of carbon atoms would have a mass of 12g

2)Aluminium has a relative atomic mass of 27, so 1mol of aluminium atoms would have a mass of ___g

3)Sodium hydroxide has a relative atomic mass of 40, so 2mols of NaOH would have a mass of ____g

21/04/23

Molar CalculationsMolar Calculations

No. of moles = Mass (g)

Molar mass (g/mol)

N = m

M

Some example questions:

1)Calculate the mass of 4mol of lithium

2)Calculate the mass of 2mol of sodium

3)Calculate the number of moles in 36g of carbon

4)Calculate the number of moles in 88g of carbon dioxide

5)Calculate the number of moles in 27g of water

21/04/23

A note about volume…A note about volume…The two most commonly used units of volume in chemistry are the cm3 and the dm3:

1cm3

1dm3 (= 1000cm3)

1) Convert 1250cm3 into dm3

2) Convert 1cm3 into dm3

3) Convert 0.056dm3 into cm3

4) Convert 1.28dm3 into cm3

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ConcentrationConcentrationConcentration means “how much of a chemical there is in a fixed volume” and can be measured in g/dm3 or mol/dm3.

A solution of low concentration

(“dilute”)

A solution of high concentration

(“strong”)

21/04/23

Questions on ConcentrationQuestions on ConcentrationTo calculate the concentration of a substance you could use one of these formulae:

Conc. = Mass of substance (g)

Volume of solvent (dm3)

Conc. = Amount of solute (mol)

Volume of solvent (dm3)

Calculate, with units, the concentration of the following:

1) A solution of 10g salt in 1dm3 of water

2) 2mol of hydrochloric acid in 500cm3 of water

3) 10kg of salt in 200dm3 of water

4) 0.5mol of sodium hydroxide in 100cm3 of water

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Converting concentrationsConverting concentrationsTo convert g/dm3 into mol/dm3 you can use the following formula:

Concentration = Concentration (g/dm3)

(mol/dm3) Molar mass

Convert the following:

1) 0.5mol/dm3 of sodium hydroxide into g/dm3.

2) 2mol/dm3 of HCl into g/dm3.

3) 20g/dm3 of NaCl into mol/dm3.

4) 500g/dm3 of CaCl2 into mol/dm3.

21/04/23

Numbers of molesNumbers of molesConsider two liquids:

Now consider two gases:

20cm3 of 0.1mol/dm3 of hydrochloric acid

20cm3 of 0.1mol/dm3 of sodium hydroxide

These two beakers contain the same number of moles

20cm3 of helium at room temperature and pressure

20cm3 of argon at room temperature and pressure

These two gases contain the same number of moles

21/04/23Universal Indicator and the pH Universal Indicator and the pH scalescale

Strong acid Strong alkali

Neutral

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Universal Indicator is a mixture of liquids that will produce a range of colours to show how strong the acid or alkali is:

Stomach acid

Lemon juice

Water Soap Oven cleaner

Baking powder

An acid contains hydrogen ions, H+

An alkali contains hydroxide ions, OH-

21/04/23Neutralisation reactionsNeutralisation reactionsWhen acids and alkalis react together they will NEUTRALISE each other:

OHNa

Sodium hydroxide

ClH

Hydrochloric acid

The sodium “replaces” the hydrogen from HCl

ClNa

Sodium chloride

H2O

Water

General equation: H+(aq) + OH-

(aq) H2O(l)

21/04/23

Common acids and alkalisCommon acids and alkalis

Acids Alkalis

Hydrochloric acid, HCl

Sodium hydroxide, NaOH

Nitric acid, HNO3

Sulphuric acid, H2SO4

Potassium hydroxide, KOH

Magnesium hydroxide, Mg(OH)2

Calcium hydroxide, Ca(OH)2

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TitrationTitration

5) Repeat until you get similar results

4) Slowly add the alkali until the mixture in the flask turns pink

3) Add phenolphthalein indicator to the flask

2) Accurately measure out 25cm3 of acid and place it in the conical flask

1) Fill a burette with sodium hydroxide solution of known concentration

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Using the correct indicatorUsing the correct indicator

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Universal Indicator is a mixture of liquids that will produce a range of colours to show how strong the acid or alkali is:

Strong acid Neutral Strong alkali

Because of the gradual colour changes it’s not a very good indicator to use for titration. It’s better to use an indicator with a sudden colour change:

Indicator Colour in acid Colour in alkali

Litmus Red Blue

Phenolphthalein Colourless Pink

Screened methyl orange Purple Green

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Using the correct indicatorUsing the correct indicator

Strong acid + strong alkali – use any indicator

Strong acid + weak alkali – use methyl orange indicator

Weak acid + weak alkali – use phenolphthalein indicator

21/04/23

Titration EquationsTitration Equations

The key steps:

Q. 0.05dm3 of HCl neutralises 0.1dm3 of NaOH of concentration 0.5mol dm-3. What is the concentration of the

acid?

1) Look at the equation to compare the numbers of moles:

HCl + NaOH NaCl + H2O

Notice that 1 mole of HCl neutralises 1 mole of NaOH

2) Use this equation:

No. of moles = concentration x volume

a) So, the number of moles of NaOH is (0.5 x 0.1) = 0.05mol

b) According to the equation, this will neutralise 0.05mol of HCl

c) Therefore we have (0.05mol/0.05dm3) = 1mol dm-3 HCl

21/04/23

Titration EquationsTitration Equations1) 0.2dm3 of HCl neutralises 0.1dm3 of NaOH of

concentration 0.5mol dm-3. What is the concentration of the acid?

2) H2SO4 of concentration 0.4mol dm-3 neutralises 0.1dm3 of NaOH of concentration 0.2mol dm-3. How much acid was used?

HCl + NaOH NaCl + H2O

H2SO4 + 2NaOH Na2SO4 + 2H2O

21/04/23Topic 3 – Electrolytic Topic 3 – Electrolytic ProcessesProcesses

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ElectrolytesElectrolytesAn electrolyte is an ionic substance that has been melted or dissolved in water so that the ions are free to move:

Cl- Na+ Cl-

Na+ Cl- Na+

Cl- Na+ Cl-

Na+ Cl- Na+

21/04/23ElectrolysisElectrolysis

++++

----

Positive electrode

(“anode”)

Cu2+

Cu2+

Cu2+

Negative electrode

(“Cathode”)Cl-

Cl-

Cl-

Electrolyte solution

containing copper ions

(cations) and chloride ions (anions)

21/04/23

ElectrolysisElectrolysisDuring electrolysis the substance being broken down is called the “electrolyte”.

= chloride ion

= copper ion

When we electrolysed copper chloride the _____ chloride ions moved to the ______ electrode and the ______ copper ions moved to the ______ electrode – OPPOSITES ATTRACT!!!

21/04/23Redox reactionsRedox reactions“Redox” reactions happen during electrolysis:

These two processes are called REDOX REACTIONS

OILRIG – Oxidation Is Loss of electrons

Reduction Is Gain of electrons

At the positive electrode (anode) the negative ions LOSE electrons

to become neutral – this is OXIDATION

At the negative electrode (cathode) the positive ions GAIN

electrons to become neutral – this is REDUCTION

21/04/23Electrolysis half equationsElectrolysis half equationsWe need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride):

2 2

2

At the negative electrode the positive ions GAIN electrons to

become neutral copper ATOMS. The half equation is:

Cu2+ + e- Cu

At the positive electrode the negative ions LOSE electrons to

become neutral chlorine MOLECULES. The half equation is:

Cl- - e- Cl2

21/04/23Electrolysis of molten sodium Electrolysis of molten sodium chloridechloride

++++

----

Positive electrode

(“anode”)

Na+

Na+

Na+

Negative electrode

(“Cathode”)Cl-

Cl-

Cl-

Write half equations for these reactions and state where oxidation and reduction occur

Sodium is a useful metal – it can be used in street lights and as a coolant for nuclear reactors. It can be made

from the electrolysis of molten sodium chloride:

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Positive electrode

Negative electrode

Electrolysis of Salt WaterElectrolysis of Salt Water

Sodium chloride solution (salt water)

NaCl(aq) Sodium hydroxide (NaOH(aq))

When solutions are electrolysed (instead of the molten compound) the results are different. Consider the electrolysis of salty water (a

solution of sodium chloride):

Chlorine gas (Cl2) Hydrogen gas (H2)

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Electrolysis of SolutionsElectrolysis of SolutionsThe electrolysis of sodium chloride solution brings different results to the electrolysis of molten sodium chloride because of the presence of hydrogen (H+) and hydroxide (OH-) ions. Two rules:

1) At the anode the “simplest” ion is discharged – e.g., in the electrolysis of a chloride the Cl- ion would be discharged (instead of the OH- ion) whereas in the electrolysis of a sulphate the OH- ion would be discharged (instead of the SO4

2- ion). The OH- ion will then form oxygen at the anode.

2) At the cathode a metal will be discharged if its less reactive then hydrogen. If it’s more reactive than hydrogen then hydrogen will be discharged.

++++

----

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Products from electrolysisProducts from electrolysisGiven these two rules, complete the following table:

Electrolyte Product at cathode

Product at anode

Copper chloride solution

Copper sulfate solution

Sodium sulfate solution

Molten lead bromide

Copper Chlorine

Copper Oxygen

Hydrogen Oxygen

Lead Bromine

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Purifying CopperPurifying Copper

++++

----

Solution containing copper ions

Impure copper

Cu2+

Cu2+

Cu2+

Pure copper

At the positive electrode:

Cu(s) Cu2+(aq) + 2e-

At the negative electrode:

Cu2+(aq) + 2e- Cu(s)

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ElectroplatingElectroplating

++++

----

Solution containing silver ions

Silver electrode

Object to be plated

Ag+

Ag+

Ag+

21/04/23Topic 4 – Gases, Equilibria and Topic 4 – Gases, Equilibria and AmmoniaAmmonia

21/04/23

Revision about VolumeRevision about VolumeThe two most commonly used units of volume in chemistry are the cm3 and the dm3:

1cm3

1dm3 (= 1000cm3)

1) Convert 1250cm3 into dm3

2) Convert 1cm3 into dm3

3) Convert 0.056dm3 into cm3

4) Convert 1.28dm3 into cm3

21/04/23

Revision about MolesRevision about MolesConsider two liquids:

Now consider two gases:

20cm3 of 0.1mol/dm3 of hydrochloric acid

20cm3 of 0.1mol/dm3 of sodium hydroxide

These two beakers contain the same number of moles

20cm3 of helium at room temperature and pressure

20cm3 of argon at room temperature and pressure

These two gases contain the same number of moles

21/04/23Calculating Volumes of Calculating Volumes of GasesGases

An important fact: 1 mole of a gas at room temperature and pressure occupies a volume of

24dm3.1) What is the volume of 2 moles of oxygen?

2) What is the volume of 0.25 moles of carbon dioxide?

3) How many moles would be in 8dm3 of nitrogen?

4) How much volume would 80g of argon occupy?

5) A balloon contains 12dm3 of carbon dioxide. What is the mass of this much CO2?

21/04/23Calculating the mass of a Calculating the mass of a productproduct

E.g. what mass of magnesium oxide is produced when 60g of magnesium is burned in air?

Step 1: READ the equation:

2Mg + O2 2MgO

IGNORE the oxygen in step 2 – the question

doesn’t ask for it

Step 3: LEARN and APPLY the following 3 points:

1) 48g of Mg makes 80g of MgO

2) 1g of Mg makes 80/48 = 1.66g of MgO

3) 60g of Mg makes 1.66 x 60 = 100g of MgO

Step 2: WORK OUT the relative formula masses (Mr):

2Mg = 2 x 24 = 48 2MgO = 2 x (24+16) = 80

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Work out Mr: 2H2O = 2 x ((2x1)+16) = 36 2H2 = 2x2 = 4

1. 36g of water produces 4g of hydrogen

2. So 1g of water produces 4/36 = 0.11g of hydrogen

3. 6g of water will produce (4/36) x 6 = 0.66g of hydrogen

Mr: 2Ca = 2x40 = 80 2CaO = 2 x (40+16) = 112

80g produces 112g so 10g produces (112/80) x 10 = 14g of CaO

Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204 4Al = 4x27 = 108

204g produces 108g so 100g produces (108/204) x 100 = 52.9g of Al2O3

1) When water is electrolysed it breaks down into hydrogen and oxygen:

2H2O 2H2 + O2

What mass of hydrogen is produced by the electrolysis of 6g of water?

3) What mass of aluminium is produced from 100g of aluminium oxide?

2Al2O3 4Al + 3O2

2) What mass of calcium oxide is produced when 10g of calcium burns?

2Ca + O2 2CaO

21/04/23Calculating the volume of a Calculating the volume of a productproduct

REMEMBER THIS - At normal temperature and pressure the Relative Formula Mass (Mr) of a gas will occupy a volume of 24

litrese.g. 2g of H2 has a volume of 24 litres

32g of O2 has a volume of 24 litres

44g of CO2 has a volume of 24 litres etc

Q. When water is electrolysed it breaks down into hydrogen and oxygen:

2H2O 2H2 + O2

What VOLUME of hydrogen is produced by the electrolysis of 6g of water?• On the previous page we said that the MASS of hydrogen produced was 0.66g

• 2g of hydrogen (H2) will occupy 24 litres (from the red box above),

• So 0.66g will occupy 0.66/2 x 24 = 8 litres

21/04/23Example questionsExample questions1) What volume of hydrogen is produced when 18g of water is

electrolysed?

2H2O 2H2 + O2

2) Marble chips are made of calcium carbonate (CaCO3). What volume of carbon dioxide will be released when 500g of CaCO3 is reacted with dilute hydrochloric acid?

CaCO3 + 2HCl CaCl2 + H2O + CO2

3) Magnesium will react with hydrochloric acid. What volume of hydrogen would be produced if you reacted 1g of magnesium with excess acid?

Mg + 2HCl MgCl2 + H2

21/04/2321/04/23

Reversible ReactionsReversible ReactionsSome chemical reactions are reversible. In other words, they can go in either direction:

A + B C + D

NH4Cl NH3 + HCl

e.g. Ammonium chloride

Ammonia + hydrogen chloride

If a reaction is EXOTHERMIC in one direction what must it be in the opposite direction?

For example, consider copper sulphate:

Hydrated copper sulphate (blue)

Anhydrous copper sulphate (white)

+ Heat

+ Water

CuSO4 + H2OCuSO4.5H2O

21/04/2321/04/23

Reversible ReactionsReversible ReactionsWhen a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants are added or taken away) an EQUILIBRIUM is achieved – in other words, the reaction goes at the same rate in both directions (a “dynamic equilibrium”):

A + B C + D

Endothermic reactions

Increased temperature:

Decreased temperature:

A + B C + D

A + B C + D

More products

Less products

Exothermic reactions

Increased temperature:

Decreased temperature:

A + B C + D

Less products

More products

A + B C + D

21/04/2321/04/23

Making AmmoniaMaking Ammonia

Nitrogen + hydrogen Ammonia N2 + 3H2 2NH3

•High pressure

•450O C

•Iron catalystRecycled H2 and N2

Nitrogen

Hydrogen

Mixture of NH3, H2 and N2. This is cooled causing NH3 to liquefy.

Fritz Haber, 1868-1934

Guten Tag. My name is Fritz Haber and I won the Nobel Prize for chemistry. I came up with the Haber

Process that uses nitrogen from the air and hydrogen from natural gas to make ammonia:

To produce ammonia from nitrogen and hydrogen you have to use three conditions:

21/04/2321/04/23Haber Process: The Haber Process: The economicseconomicsA while ago we looked at reversible reactions:

A + B C + D

Endothermic, increased temperature

A + B C + D

Exothermic, increase temperature

ExothermicEndothermic

1) If temperature was DECREASED the amount of ammonia formed would __________...

2) However, if temperature was INCREASED the rate of reaction in both directions would ________ causing the ammonia to form faster

3) If pressure was INCREASED the amount of ammonia formed would INCREASE because there are less molecules on the right hand side of the equation

Nitrogen + hydrogen Ammonia

N2 + 3H2 2NH3

21/04/2321/04/23

Haber Process SummaryHaber Process Summary

•200 atm pressure

•450O C

•Iron catalyst

Recycled H2 and N2

Nitrogen

Hydrogen

Mixture of NH3, H2 and N2. This is cooled causing NH3 to liquefy.

To compromise all of these factors, these conditions are used:

A low temperature increases the yield of ammonia but is too slow

A high temperature improves the rate of reaction but decreases the yield too much

A high pressure increases the yield of ammonia but costs a lot of money

21/04/23EutrophicationEutrophicationAmmonia is used to make fertilisers. One possible problem with fertilisers is eutrophication. Eutrophication is when lakes become stagnant due to careless use of fertiliser…

1) Inorganic fertilisers used on fields are washed into the lake

3) This growth causes overcrowding and many plants die due to lack of enough light or food

2) The fertiliser causes increased growth in water plants

21/04/23

EutrophicationEutrophication4) Microorganisms and bacteria increase in number due to the extra dead material

5) These microorganisms use up the oxygen in the lake during respiration

6) The lack of oxygen causes the death of fish and other aquatic animals

Can’t…breathe…

21/04/23

EutrophicationEutrophication4) Microorganisms and bacteria increase in number due to the extra dead material

5) These microorganisms use up the oxygen in the lake during respiration

6) The lack of oxygen causes the death of fish and other aquatic animals

21/04/23

Topic 5 – Organic ChemistryTopic 5 – Organic Chemistry

21/04/23

EthanolEthanol

Ethanol is produced from ethene, a chemical produced from the fractional distillation of crude oil and involving cracking using a catalyst at high temperature and pressure:

Ethanol is a “clean burning” energy source and produces little or no greenhouse gases. How is it made? Ford Escape E85 –

runs on 85% ethanol

The “fossil fuel” way

The “renewable” way

Ethene + steam ethanol

Ethene is produced by “cracking” oil

Sugar ethanol + carbon dioxide

This process uses yeast as an enzyme

...or by the fermentation of sugar from standard crops like sugar cane and corn, under warm and anaerobic conditions:

21/04/23Making ethanol from Making ethanol from etheneethene

EtheneReaction vessel with high temperature and pressure Ethanol

Unused ethene recycled

Ethene + water ethanol

C2H + H2O C2H5OH

21/04/23

Distillation revisionDistillation revision

This apparatus can be used to separate water and ethanol because they have different _____ ______. The ______ will evaporate first, turn back into a _______ in the condenser and collect in the _______. The water remains in the round flask, as long as the _______ does not exceed water’s boiling point. This method can be used to separate crude oil.

Words – temperature, boiling points, ethanol, beaker, liquid

21/04/23

Key facts about ethanolKey facts about ethanolThe following facts apply to ethanol:

1) They all dissolve in water to form a neutral solution

2) They are used as fuels and solvents and ethanol is the main alcohol in alcoholic drinks

3) Ethanol can be dehydrated to form ethene

Remember us? When we’re making ethanol there are two main things we need to consider – how available are

the raw materials (sugar cane or crude oil) and how good is the final

product?

21/04/23

AlkanesAlkanesAlkanes are SATURATED HYDROCARBONS. What does this mean?

HYDROCARBONS are molecules that are made up of hydrogen and carbon atoms

SATURATED means that all of these atoms are held together by single COVALENT bonds, for example:

Ethane

Alkanes are fairly unreactive (but they do burn well). The general formula for an alkane is CnH2n+2

C C

HH

H

HH

H

Butane

C C

HH H

HH

H C C H

H

HH

21/04/23General Formulae for General Formulae for AlkanesAlkanesAlkanes form a homologous series (they have the same

general formula)…

General formula for alkanes = CnH2n+2

Butane (n=4)

H

C C

H

HH

H

C C

H

HH

H H

Methane (n=1)

H

C H

H

H

Ethane (n=2)

H

H

C C

H

HH

H

Propane (n=3)

H

C H

H

H

C C

H

HH

H

21/04/23

AlkenesAlkenesAlkenes are different to alkanes; they contain DOUBLE COVALENT bonds (a bond that has two shared electrons). For example:

Ethane Ethene

Butane Butene

This double bond means that alkenes have the potential to join with other molecules – this make them REACTIVE.

ALK

AN

ES

ALK

EN

ES

21/04/23General Formulae for General Formulae for AlkenesAlkenes

General formula for alkenes = CnH2n

Propene (n=3)

H

C H

H

H

C C

H

H

Ethene (n=2)

H

H

C C

H

H

Butene (n=4)

H

C C

H

HH

H

C C

H

H H

Alkenes also form a homologous series…

Chemicals in the same homologous series will have the same general formula, they will show a gradual

variation in one property (e.g. increasing boiling points) and have

similar chemical properties.

21/04/23

AlcoholsAlcoholsAlcohols are a homologous series with a functional group –OH. Some examples:

General formula for alkanes = CnH2n+1OH

Methanol (n=1)

H

C O

H

H H

Ethanol (n=2)

O

H

C C

H

HH

H H

Methanol is an important raw material used in the manufacture of fuels, adhesives and solvents.

Ethanol can be oxidised using agents or microbes to form ethanoic acid, the main acid in vinegar (a flavouring and preservative).

The next alcohol in this series is propanol. Write its formula and draw its chemical structure.

21/04/23

Carboxylic acidsCarboxylic acidsCarboxylic acids form a homologous series with the functional group –COOH. The presence of the –COOH gives carboxylic acids their properties.

Some facts about carboxylic acids:

1) They dissolve in water to form weak acidic solutions

2) They react with carbonates to form carbon dioxide

3) They react with metals

4) They react with bases

Methanoic acid

CO

H

H

O

Ethanoic acid

H

CH

H CO H

O

Propanoic acid

H

CH

H CO H

OH

CH

21/04/23

EstersEstersEsters are compounds with the functional group –COO-. Ethyl ethanoate is the main example and it is formed when ethanoic acid reacts with an alcohol:

Ethanoic acid + ethanol ethyl ethanoate + water

The reaction is carried out in the presence of a catalyst (e.g. concentrated sulphuric acid). They have distinctive smells and are used perfumes and food products.

Structural formula of this reaction:

Ethanoic acid

H

CH

H CO H

O

Ethanol

O

H

C C

H

HH

H H

H

C

H

H O

O

C

H

H

C

H

H

C

H

H

Ethyl ethanoate Water

O

H

H

21/04/23

Uses of EstersUses of EstersPerfumes are synthetically made from esters. Here are some facts about perfumes. Why are these things important?1) Perfumes are non-toxic

2) They are non-irritants

3) They evaporate easily

4) They do not dissolve in water

5) They don’t react with water

Polymers containing the ester functional group are also used to make polyesters. Polyesters are fibres used to

make clothing or plastic bottles and they can be recycled to make fleece.

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Healthy and Unhealthy OilsHealthy and Unhealthy OilsUnhealthy oils:

Healthy oils:

“Saturated”

“Unsaturated”

Oils and fats are both classed as esters.

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Making SoapMaking Soap1) Take an oil and boil it with concentrated alkali solution

2) The oils break down into glycerol and long chain carboxylic acids

3) The acids then react with the alkali to make a salt and water

4) So a lot of soaps are basically sodium or potassium salts of long-chain carboxylic acids

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How soap worksHow soap worksSoaps work by having a “hydrophobic” and a “hydrophilic” end. The hydrophobic end dissolves in grease and the hydrophilic end dissolves in water:

How they work:

A hydrophobic soap anion

The soap anions surround the oil and form droplets around it, which enables the grease to “lift out” of the stain.

21/04/23Turning unsaturates into Turning unsaturates into saturatessaturates

The unsaturated fat is hardened by “catalytic hydrogenation”. Hydrogenated oils have a higher melting point and so are solid at room temperature, making them useful for margarines and pastries.

600C, Nickel catalyst

As the filtered oil cools down it turns into a solid fat – useful for margarine!