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Grade 11, University Preparation Chemistry

Lesson 5 – Chemical Changes

SCH3U – Chemistry Lesson 5

Lesson 5 – Chemical Changes

Learning Objectives:

Identify synthesis and decomposition reactions Write balanced chemical equations to represent synthesis and decomposition

reactions using the IUPAC nomenclature system Investigate synthesis and decomposition reactions by testing the products such as

gases Predict the products of different types of synthesis and decomposition reactions Analyse, on the basis of research chemical reactions used in various industrial

processes that can have an impact on the health and safety of local populations

Introduction

All around us, and even inside us, substances are combining to produce new substances. Sometimes the products are useful and other times not so useful. Sometimes they can even be hazardous such as the reaction between household bleach and acidic toilet bowl cleaner.

Plastics, fabrics, pharmaceuticals, fertilizers, and pesticides are each products of a chemical reaction. These products prove that understanding chemicals and their reactions are necessary to modern society. However chemical reactions also have the potential to cause harm. In 1997, 400 000 kg of plastic at a manufacturing plant caught fire in Hamilton, Ontario. The fire took three days before it could be controlled, and in that time people were exposed to hazardous chemicals such as hydrochloric acid, and benzene. This fire is an example of an uncontrolled chemical reaction.

Observing Matter

Matter is anything that has mass and takes up volume (space). Characteristics that help chemists describe mater are called properties. A physical property can be observed without changing one kind of matter into something new. For example iron is a strong metal, with a shiny surface, and a solid at room temperature. A chemical property can be observed when one kind of matter is converted into a different kind of matter. For example iron reacts with oxygen to form a different kind of matter rust.

Some properties of matter, such as colour, and flammability are qualitative, meaning that you can describe these properties with words. Other properties of matter are quantitative, because they can be measured and expressed numerically. For example density and boiling point are both quantitative properties of matter.

The following flow chart shows how matter is classified. It is broken up into mixtures, and pure substances which are further divided into homogeneous and heterogeneous solutions and elements and compounds.

Copyright © 2009, Durham Continuing Education of 43


Classification of Matter

The Kinetic Molecular TheoryThe kinetic molecular theory states that all matter is made up of particles. These particles are in constant and continuous motion. Temperature plays an important role in this theory, it is a measure of the average speed of the particles. As temperature increases the particles gain more energy and mover faster.

According to the kinetic molecular theory, the motion of all particles results in random collisions. As the temperature of a substance increases the speed of its molecules increase, which leads to more collisions. This is one way to increase the chances of a chemical reaction taking place. Not only are collisions between molecules required, but we also need to have those molecules collide with the correct orientation or positioning. In the following figure you can see that only one orientation will result in a chemical reaction. No reaction will occur during collision 2, 3 or 4.


MATTER

Has mass and occupies space

MIXTURES

Two or more substances mixed together without chemically combining in any way

PURE SUBSTANCES

Have a definite composition and are uniform throughout the sample.

SOLUTIONS(homogeneous)

Components are uniformly distributed throughout, but not

chemically combined.

Ex: Sterling silver, Kool Aid, Salt water

MECHANICAL MIXTURES

(heterogeneous)

Components are not uniformly distributed

throughout.

Ex: Carbonated pop, Pizza

ELEMENTS

Cannot be brokendown into simpler

substances by ordinary chemical means.

Ex: C, H, O, Ca, Ne, Au

COMPOUNDS

Two or more elements that are chemically

combined with bonds.

Ex: NaCl, H2O, CO2, CH4, CH3COOH


Physical and Chemical ChangeA physical change is when the chemical identity of a substance remains the same. For example; when candle wax melts it is still candle wax just in a new state (liquid instead of solid). The same can be said for water freezing or melting. A change of state (solid, liquid, gas) is always indication that a physical change has taken place.

In a chemical change at least one new substance must be formed. This means that the reactants (starting materials) must be different than the products (end materials). For example when a candle burns it produces carbon dioxide (CO2) and water (H2O). There are several clues that a chemical change has occurred. Colour change, production of gas, change of smell, formation of a precipitate (a solid formed when two liquids are mixed together), and the release of heat or light are all examples of indicators which signal that a chemical change has taken place.

In chemical changes, the total mass of the matter present before the change is always the same as the total mass present after the change, no matter how different the new substances appear. In a chemical change particles rearrange themselves at the molecular level. This means the mass must be constant. Due to this fact all chemical reactions must follow the law of conservation of mass.



Chemical ReactionsThere are several ways to represent a chemical reaction. Word equations effectively communicate information about chemical reactions. They give the chemical names of the reactants and products. A chemical equation includes the formulae of the reactants and products as well as the proportions in which they react. These proportions are shown by writing coefficients in front of the chemical symbols for each substance.

Reactants Products

Word Equation Identifies chemicals in a

reaction by name

sodium + chlorine sodium chloride

Balanced Equation Coefficients are used to

abide by the Law of Conservation of Mass

2 Na(s) + Cl2(g) 2NaCl(s)

Practice writing out a chemical equation!

Write out the chemical equation for the following word equation:

Magnesium + Oxygen Magnesium Oxide

Step 1: Convert all chemical names into formulae

Magnesium Mg

Oxygen O2 *oxygen is O2 since it is a diatomic molecule (H, O, F, Br, I, N, and Cl are all diatomic molecules)

Magnesium Oxide Mg has a charge of +2 O has a charge of -2

Mg+2O-2

The 2 from the O becomes the subscript for Mg, while the 2 from Mg becomes the subscript for O (Mg2O2). Since both numbers are equal they can be reduced to 1. Therefore the formula becomes MgO

The chemical equation for this question is:



Mg + O2 MgO

Step 2: Balance all chemical formulae in the equation

Left Side Right Side1 Mg 1 Mg2 O 1 O we need to multiply O by 2

Left Side Right Side1 Mg 2 Mg because we multiplied MgO by 2 we now have 2 Mg and 2 O on the right

2 O 2 O

Left Side Right Side1 Mg we need to multiply Mg by 2 2 Mg2 O 2 O

Left Side Right Side2 Mg 2 Mg2 O 2 O

Both sides are equal indicating the equation is balanced

The balanced chemical equation for this question is: 2Mg + O2 2MgO

Support Questions

1. When an alka-seltzer tablet is added to a glass of water, bubbles are produced and the tablet eventually disappears. Is this a chemical or physical change? Give reasons for your answer.

2. List four changes that can be used as evidence for chemical reactions. For each change provide an example from everyday life.

3. Does the following equation adhere to the law of conservation of mass? If not, explain why.

Pb(s) + AgNO3(aq) Ag(s) + Pb(NO3)2(aq)

Synthesis Reactions



Ammonia is an important industrial product. It is prepared by combining nitrogen gas and hydrogen gas. This process is used around the world to produce agricultural fertilizer.

The reaction between nitrogen gas and hydrogen gas to produce ammonia is known as a synthesis reaction. In a synthesis reaction, two or more substances combine to form a single product. The compound formed by a synthesis reaction can be either ionic or molecular. Synthesis reactions can be represented by the general equation:

A + B C

Several synthesis reactions are associated with the combustion of gasoline. For example the burning of gasoline at high temperatures causes nitrogen in the air to react with oxygen producing nitrogen monoxide.

N2(g) + O2(g) 2 NO(g)

In cases where the reactants are elements, it is easy to recognize the reaction as a synthesis reaction. A reaction in which one or both of the reactants is a compound can still be a synthesis reaction. For example, when gasoline is burned in air, the nitrogen monoxide produced can further react with oxygen to produce nitrogen dioxide.

2 NO(g) + O2(g) 2 NO2(g)

There are several types of products that can be formed by synthesis reactions. The following table shows four possible products.

SynthesisA + B C

1. Metal and a non-metal – form an ionic bond (binary compound) Na + Cl NaCl

2. Metal or a non-metal combine with oxygen to form an oxide

2Mg + O2 2MgO C + O2 CO2

3. A metal oxide with water forms a BASE (pH > 7) MgO + H2O Mg(OH)2

4. A non-metal oxide with water forms an ACID (pH < 7) CO2 + H2O H2CO3

Practice writing out a synthesis reaction!



When sodium metal is added to a container of bromine liquid, the reaction produces sodium bromide. Represent this synthesis reaction in a word equation and a balanced chemical equation.

Step 1: Determine the word equation

sodium + bromine sodium bromide


Na(s) + Br2(l) NaBr


Left Side Right Side1 Na we need to multiply Na by 2 1 Na2 Br 1 Br we need to multiply Br by 2

Left Side Right Side2 Na 2 Na2 Br 2 Br


The balanced chemical equation for this question is: 2Na(s) + Br2(l) 2NaBr

Decomposition ReactionsDuring warm weather, nitrogen dioxide can accumulate in the atmosphere forming a brown haze known as smog. UV radiation from the sun can cause the NO2 to decompose into NO and O. This reaction is an example of a decomposition reaction.

In this type of reaction a compound decomposes to form two or more substances. The products can be elements, or compounds. Decomposition of binary compounds generally produce the two elements that make up the compound. Decomposition reactions can be represented by the general equation:

C A + B

Decomposition reactions are the basis for industrial production of many elements from natural sources. For example, the decomposition of water produces oxygen and hydrogen.



2H2O(l) 2 H2(g) + O2(g)

Fig. 1 Hoffman apparatus used in decomposition of water

There are several types of products that can be formed by decomposition reactions. The following table shows two possible products.

DecompositionC A + B

1. Decomposition of Water: 2H2O(l) 2H2(g) + O2(g)

2. Decomposition of Calcium Carbonate CaCO3 CaO + CO2

Practice writing out a decomposition reaction!

Zinc carbonate undergoes thermal decomposition to produce zinc oxide and carbon dioxide. Represent this synthesis reaction in a balanced chemical equation.


ZnCO3 ZnO + CO2



The balanced chemical equation for this question is: ZnCO3 ZnO + CO2



Support Questions

4. Classify the following reactions as synthesis, or decomposition. Predict the products of the reactions using balanced chemical equations.

a. Al(s) + F2(g)

b. KCl(s)

5. Balance the following reactions:

a. ___Fe + ___O2 ___Fe2O3

b. ___P4 + ___Cl2 ___PCl3

6. For each of the following reactions predict the products by writing a balanced chemical equation to represent the reaction. Be sure to classify the reaction type.

a. For many thousands of years, molten copper has been produced by heating the ore CuO(s).

b. A frequent problem associated with swimming pool maintenance is that the copper pipes react with aqueous chlorine which is added to kill bacteria.

Key Question #51. Chemical reactions are important reactions that occur numerous times everyday.

Your task is to research 4 different chemical reactions that occur either in your home, or in industry. For each chemical reaction, write out the word equation, balanced chemical equation, state the type of reaction, where it is used, and why it is important. (15 marks)

2. For one of the reactions you have researched, determine the impact it has had on the health and safety of local populations. Provide your results in the form of a well structured paragraph that includes an introduction and conclusion. (10 marks)


SCH3U


Lesson 6 – Displacement Reactions


Lesson 6 – Displacement ReactionsLearning Objectives:

Identify single displacement, and double displacement reactions Write balanced chemical equations to represent single, and double displacement

reactions using the IUPAC nomenclature system Investigate single, and double displacement reactions by testing the products such

as gases Predict the products of single displacement reactions, using the metal activity series

and the halogen series; and the products of double displacement reactions Plan and conduct an inquiry to demonstrate a single displacement reaction, using

elements from the metal activity series Use appropriate terminology related to chemical reactions such as precipitates

Introduction

Most metals occur naturally as ores which are metal containing minerals. To extract silver from its ore, it is reacted with cyanide. The cyanide binds to the silver making silver cyanide. This solution of silver cyanide is then reacted with zinc.

Zn(s) + 2 AgCN(aq) 2 Ag(s) +Zn(CN)2(aq)

Photography is another field in which chemical reactions are important. Early photographic developing techniques made use of copper plates coated with silver nitrate. The copper would displace the silver resulting in a photograph of silver.

Cu(s) + 2 AgNO3(aq) 2 Ag(s) + Cu(NO3)2(aq)

These two types of reactions are referred to as single displacement reactions. Single displacement reactions are usually metallurgical processes.

There are three clues that tell us that a reaction is taking place; if a precipitate (solid) is formed, if a gas is produced (bubbles), or if the solution becomes more neutral (less acidic or basic).

Analytical chemists often make use of the potential for precipitate formation in double displacement reactions to determine the presence of a particular chemical in a sample. This type of analysis is referred to as a qualitative analysis, as only the identity of the chemical is determined, not the amount of chemical present.



Single Displacement ReactionsIn a single displacement reaction a free element replaces another similar element in a compound to produce a different compound, and a different free element. Single displacement reactions can be represented by the general equation:

A + BC AC + B

An example of a single displacement reaction is the thermite reaction between aluminum and iron III oxide. A thermite reaction is not explosive, but creates short bursts of extremely high temperatures focused on a very small are for a short period of time.

2 Al(s) + Fe2O3(s) Al2O3(s) + 2 Fe(l)

The element which is displaced from the compound is always the more metallic compound. Reminder: reactivity of metals is greatest at the bottom left of the periodic table.

The displaced element isn’t always a metal. Another common single displacement reaction displaces hydrogen from acids by using metals. The very reactive metal will react with water as in the example below.

Ca(s) + 2 H2O(l) Ca(OH)2(aq) + H2(g)

Calcium metal in this example reacts with water to form calcium hydroxide and hydrogen gas.

Less reactive metals such as iron, do not react with water at all, but can react with acids.

Fe(s) + 2 HCl(aq) FeCl2(aq) + H2(g)

Scientists have gathered empirical data in order to be able to list elements in order of their reactivity. These lists are known as the activity series.

There are two patterns by which all single displacement reactions occur. The following table shows both possibilities.

Single DisplacementA + BC B + ACDE + F DF + E

1. Metal replaces metal Mg + 2AgNO3 2Ag + Mg(NO3)2

2. Non-metal replaces non-metal Br2 + CaI2 I2 + CaBr2

The Activity SeriesAn activity series of metals appears below. It contains a list of metallic elements arranged in order of decreasing reactivity. Whether or not a single displacement



reaction will occur can be predicted by using the activity series. Each metallic element will displace a metal ion that appears below it in the series.

Zn(s) + FeCl2(aq) Fe(s) + ZnCl2(aq)

Since zinc is higher than iron on the activity series it can displace the iron. A reaction of tin and iron II chloride would not occur however since tin is below iron in the activity series.

Sn(s) + FeCl2(aq) no reaction

ACTIVITY SERIES OF THE METALS


Most Reactive

LithiumPotassium

BariumCalciumSodium

MagnesiumAluminum

ZincChromium

IronCadmium

CobaltNickel

TinLead

Hydrogen*CopperMercury

SilverPlatinum

Gold

Least Reactive


ACTIVITY SERIES OF THE HALOGENS

Practice writing out a single displacement reaction!

Predict the products if any of the reaction between chlorine gas and a solution of sodium bromide obtained from sea water. Represent the reaction in a balanced equation.

Step 1: Write out the reactants for this reaction

Cl2(g) + NaBr(aq)

Step 2: Use the activity series to see if the reaction will occur

Cl is higher on the activity series of halogens than bromine, this means it will displace Br, and the reaction will occur.

Step 3: Write out the products of the reaction

Cl2(g) + NaBr(aq) NaCl(aq) + Br2(g)

Step 4: Balance your reaction

Cl2(g) + 2 NaBr(aq) 2 NaCl(aq) + Br2(g)

The balanced chemical equation for this question is: Cl2(g) + 2 NaBr(aq) 2 NaCl(aq) + Br2(g)


Most Reactive

FluorineChlorineBromineIodine

Least Reactive


Support Questions

1. For each of the following, use the activity series to determine which single displacement reactions will occur. For the reactions that do occur, predict the products and complete and balance the equation.

a. Pb(s) + HCl(aq)

b. Ca(s) + H2O(l)

c. Sn(s) + AgNO3(aq

d. Al(s) + ZnSO4(aq)

2. What types of reactants are likely to be involved in a single displacement reaction?

Double Displacement ReactionsIn a double displacement reaction two compounds swap cations (positive ions), displacing each other to form two new compounds. Double displacement reactions can be represented by the general equation:

AB + CD AD + CB

Magnesium chloride, a soluble ionic compound, occurs naturally in sea water. In commercial preparation of magnesium, calcium hydroxide is added to large quantities of sea water, resulting in the production of a white powder, magnesium hydroxide. This is an example of a double displacement reaction.

MgCl2(aq) + Ca(OH)2(aq) Mg(OH)2(s) + CaCl2(aq)

Double displacement reactions involve two ionic compounds as reactants. As the equation above shows, the ions change partners to form the products. This type of reaction commonly occurs in aqueous solutions. An aqueous solution is when a compound is dissolved in water. It is shown in a chemical equation by adding (aq) to the chemical formula.

In order to predict products of single and double displacement reactions we need to understand solutions, and learn how to determine whether a substance will dissolve in water, or form a precipitate. A precipitate is a solid formed from a reaction that takes place in solution.



There are two patterns by which all double displacement reactions occur. The following table shows both possibilities.

Double DisplacementAB + CD AD + CB

1. Metals exchange places with metals, and non-metals exchange places with non-metals.

Pb(NO3)2 + 2KI PbI2 + 2KNO3

2. Neutralization Reactions ACID + BASE IONIC SALT + WATER

HCl + NaOH NaCl + H2O

Solubility

A solution is a homogenous mixture of a solute and a solvent. A solute is a substance that dissolves in a solvent to form a solution. A solvent is the medium in which a solute dissolves. Every solute has its own solubility in a given solvent. Solubility is a property of a substance that measures the maximum amount of a substance that will dissolve in a fixed quantity of a given solute at a specified temperature.

For example, if salt is slowly added to water, and we stir after each addition, the salt will dissolve until the salt solution reaches its maximum concentration. At this point, any extra salt that is added will remain solid.

If the product of a double displacement reaction is very soluble it will stay in solution, and we assign it the subscript (aq). If the product is only slightly soluble, it is likely that more will be produced that can dissolve. If the product is a solid it will be visible as a precipitate and assigned the subscript (s). If a gas appears it will be given the subscript (g).

The following table outlines the solubilities of a large number of ionic compounds. It can be used to predict whether the products of a reaction will produce a precipitate or remain in solution.



In the reaction of barium chloride and potassium sulphate a precipitate of barium sulphate is formed. The potassium chloride is aqueous since everything except Ag, Pb, and Hg is soluble in Cl. Barium sulphate however is insoluble since they are not soluble when mixed with Ag, Ca, Sr, Ba or Pb.

BaCl2 (aq) + K2SO4(aq) 2 KCl(aq) + BaSO4(s)

Some double displacement reactions produce a gas product. For example, sodium sulphide solution and hydrochloric acid react to produce hydrogen sulphide gas.

Na2S (aq) + 2 HCl(aq) 2 NaCl(aq) + H2S(g)



Practice writing out a double displacement reaction!

Predict the products formed by a double displacement reaction in aqueous solution of copper II nitrate and magnesium chloride. Write a balanced chemical equation indicating the physical state of the products formed.

Step 1: Write out the reactants for this reaction

Cu(NO3)2(aq) + MgCl2(aq)

Step 2: Predict the products of the double displacement reaction by switching the two metals (cations)

Cu(NO3)2(aq) + MgCl2(aq) CuCl(aq) + Mg(NO3)2(aq)

Step 3: Write out the states of the products by using the solubility table

Cu(NO3)2(aq) + MgCl2(aq) CuCl2(aq) + Mg(NO3)2(aq)

CuCl2 is aqueous since Cl is soluble with everything except Ag, Pb, and Hg.Mg(NO3)2 is also aqueous since NO3 is soluble with everythingWhen both products are aqueous solutions the reaction is not likely to take place.


Cu(NO3)2(aq) + MgCl2(aq) CuCl2(aq) + Mg(NO3)2(aq)

The balanced chemical equation for this question is:

Cu(NO3)2(aq) + MgCl2(aq) no reaction

Summary-Predicting Double Displacement ReactionsDouble Displacement reactions are likely to proceed if:

one of the products is a precipitate one of the products is a gas, or the reactants are an acid and a base, and the result is a neutralization reaction

producing a salt and water.



Support Questions

3. Predict the solubility in water of each of the following compounds. Write out the chemical formula as well as its state of matter.

a. potassium nitrateb. aluminum sulphatec. ammonium carbonate

4. Classify each reaction as single or double displacement.

a. Cu(s) + 2 AgNO3(aq) 2 Ag(s) + Cu(NO3)2(aq)

b. b) KI(aq) + AgNO3(aq) AgI(s) + KNO3(aq)

5. Predict the products formed by double displacement reactions in aqueous solution of each of the following pairs of compounds. In each case write a balanced chemical equation indicating the physical state of the products formed.

a. copper II nitrate and magnesium chlorideb. barium hydroxide and iron III sulphatec. ammonium sulphide and iron II sulphate

Key Question #6

1. Chromium, manganese, and barium are all examples of metals that can be prepared in a pure form by combining oxides of theses elements with reactive metals. When aluminum is chosen as the reactive metal, the process is referred to as the Goldschmidt process or the Thermite process.

a. What type of reaction is the Goldschmidt process? (1 mark)b. Write the formulas for the common oxides formed by chromium, manganese,

and barium. (3 marks)c. Predict the products formed by each of the three oxides in the Goldschmidt

process, using a balanced chemical equation. (6 marks)

2. Beryllium was first isolated as a relatively pure metal when investigators heated solid beryllium chloride with solid potassium.

a. Predict the products of this reaction in a balanced equation; also indicate what type of reaction this is. (2 marks)



Key Question #6 (continued)

b. Beryllium chloride, is still used in the production of beryllium. However, it can cause lung cancer if small particles of the compound are inhaled, it can also damage skin with repeated contact. Another danger of working with this compound is that it reacts with the water in air to produce hydrochloric acid, which is highly corrosive. Suggest at least three safety precautions that would be needed in the industrial storage and use of this substance. (3 marks)

3. Analytical chemists are trying to determine the identity of an unknown solution. They have narrowed it down to two possibilities, silver nitrate or potassium nitrate. You have been assigned the task of determining how to finish testing the solution to reveal its identity. Use your knowledge of double displacement reactions, and the solubility table to come up with a laboratory procedure which will identify the unknown solution. Be sure to include a purpose (1 mark), hypothesis (2 marks), materials (2 marks) and procedure (5 marks). Hint: Find a solution that you can react with both unknowns that will produce different results. (one soluble, and one insoluble)


SCH3U


Lesson 7 – Combustion Reactions


Lesson 7 – Combustion Reactions


Identify combustion reactions Write balanced chemical equations to represent combustion reactions using the

IUPAC nomenclature system Design an inquiry to demonstrate the difference between complete and incomplete

combustion reactions Explain the difference between a complete combustion reaction and an incomplete

combustion reaction

Introduction

Getting up to a warm home, having a hot shower, cooking breakfast, and catching the bus to school are all everyday things that are made possible by the combustion of fossil fuels. Less obvious things that are just as dependent on combustion reactions include the things we have such as; our clothes, shelter, books, and entertainment.

Our way of life depends on the combustion of hydrocarbons, If the sources of hydrocarbons were depleted our way of life would dramatically change. Cellular respiration is also an example of a combustion reaction. Glucose is burned to supply living cells with energy. The products of the reaction are carbon dioxide and water. These are the same products produced when hydrocarbons are burned.

Combustion ReactionsEvery time we flick a lighter, strike a match, fire up the barbeque, or stoke a camp we are starting a combustion reaction. Combustion reactions are more commonly known as burning. They can be identified by the fact that they produce heat. A combustion reaction is the reaction of a substance with oxygen to produce oxides and energy. For combustion reactions to occur three things must be present; fuel, oxygen, and heat

The combustion of hydrocarbons can be represented by the general equation:

hydrocarbon + O2 CO2 + H2O

There are several patterns by which all combustion reactions occur. The following table shows the possibilities. The one we will be concentrating on is the combustion of hydrocarbons.



Combustion

Metal + oxygenmetal oxide

Nonmetal + oxygen nonmetal oxide

Hydrocarbon+ oxygenCO2 + H2O

S + O2 SO2

CH4 + 2 O2 CO2 + 2 H2O

Complete Combustion In complete combustion a hydrocarbon (a compound which contains hydrogen and carbon) reacts with oxygen to produce carbon dioxide and water vapour. Petroleum is used as fuel in combustion engines. The following combustion reaction of petroleum shows that it produces energy.

2 C8H18(l) + 25 O2(g) 16 CO2(g) + 18 H2O(g) + energy

So much carbon dioxide is produced by burning fossil fuels that human activities are leading to the increase of carbon dioxide in our atmosphere. This increase in carbon dioxide may also be contributing to the increase of the Earth’s average temperature. (Global warming) The exploitation of fossil fuels has its issues. Without them, we wouldn’t be living in our current way of life, but with them we may be sacrificing our children’s futures.

Practice writing out a complete combustion reaction!

Write the word, and balanced chemical equation for the complete combustion of butane gas, C4H10.

Step 1: Write out the word equation for this reaction

butane gas + oxygen gas carbon dioxide gas + water vapour

Step 2: Write out the chemical equation for this reaction

C4H10(g) + O2(g) CO2(g) + H2O(g)


2 C4H10(g) + 13 O2(g) 8 CO2(g) + 10 H2O(g)



The balanced chemical equation for this question is: 2 C4H10(g) + 13 O2(g) 8 CO2(g) + 10 H2O(g)

Support Questions

1. a. Why are there signs at gas stations warning motorists to turn off their vehicles engines, refrain from smoking, and avoid causing sparks?

b. What type of reaction is the concern?

c. What are the necessary conditions for this reaction to proceed?

2. Write out the balanced chemical equation showing the complete combustion of jet fuel, C14H30(l).

Incomplete Combustion

Incomplete combustion reacts an element of compound with oxygen to produce some oxides with less oxygen content such as carbon monoxide. Ideally the combustion of hydrocarbons produces only carbon dioxide and water vapour, but if there isn’t enough oxygen available the combustion of hydrocarbons can also produce carbon monoxide and or carbon (soot).

The larger the hydrocarbon the more likely it is to undergo incomplete combustion. This is why incomplete combustion is more of a problem for gasoline (C8H18) than natural gas (CH4). The following reactions show the complete and incomplete combustion of gasoline. Notice that when less oxygen is used, less carbon dioxide, and more carbon monoxide or carbon is produced.

Complete combustion

C8H18(l) + 25/2 O2(g) 8 CO2(g) + 9 H2O(g)

Incomplete combustion

C8H18(l) + 12 O2(g) 7 CO2(g) + CO(g) + 9 H2O(g)

C8H18(l) + 23/2 O2(g) 6 CO2(g) + 2 CO(g) + 9 H2O(g)

C8H18(l) + 5 O2(g) CO(g) + 7C(s) + 9 H2O(g)

Incomplete combustion of a fuel such as octane is undesirable because it produces less energy, leaves black residue (carbon) and produces toxic carbon monoxide.

Carbon monoxide is a colourless, odourless gas found in air. Car emissions in large cities during rush hour can cause major health problems. If there is no wind, and the



temperature is high, headaches are very common. They are a sign of mild carbon monoxide poisoning. Parking in a car with the motor running for extended periods of time can result in carbon monoxide poisoning if there are leaks in the exhaust system. Faulty exhaust systems have been the cause of deaths of children and other passengers in the back seat.

Practice writing out an incomplete combustion reaction!

Provide the balanced chemical equation for one of the possible chemical equations for the incomplete combustion of butane gas, C4H10.

Step 1: Write out the chemical equation for this reaction.

There are three possibilities

C4H10(g) + O2(g) 3 CO2(g) + CO(g) + H2O(g)

C4H10(g) + O2(g) 2 CO2(g) + 2 CO(g) + H2O(g)

C4H10(g) + O2(g) CO(g) + C(s) + H2O(g)


C4H10(g) + 6 O2(g) 3 CO2(g) + CO(g) + 5 H2O(g)

2 C4H10(g) + 11 O2(g) 4 CO2(g) + 4 CO(g) + 10 H2O(g)

C4H10(g) + 3 O2(g) CO(g) + 3C(s) + 5 H2O(g)

The balanced chemical equation for this question is one of the following;

C4H10(g) + 6 O2(g) 3 CO2(g) + CO(g) + 5 H2O(g)

2 C4H10(g) + 11 O2(g) 4 CO2(g) + 4 CO(g) + 10 H2O(g)

C4H10(g) + 3 O2(g) CO(g) + 3C(s) + 5 H2O(g)

Thought Lab: Combustion Reactions

Purpose: What are the products of the combustion of natural gas?

Evidence: A beaker of cold water moved though the flame condenses a clear,



colourless liquid. No black deposit is observed. Limewater was added to the gas produced, and the result was a cloudy mixture. This is indicative of the presence of carbon dioxide.

Analysis: According to the evidence provided what is the answer to the purpose?

Evaluation: a. Evaluate the evidence collected. For example, is it possible to determine whether the combustion was complete?

b. Suggest an improvement to this experiment to be more certain about the type of combustion.

Support Questions

3. How do the products of complete combustion, and incomplete combustion differ?

4. Heptane, C7H16(l) is a component of gasoline. Write a balanced chemical equation for:

a. the complete combustion of heptane

b. the incomplete combustion of heptane, assuming equal amounts of the two carbon oxides are the only carbon containing products.

The Greenhouse EffectCarbon dioxide and water are products of the combustion of carbon compounds including fossil fuels and wood in forest fires. These gases are also released in volcanic eruptions and by living organisms during cellular respiration. All of these sources have been present for billions of years, and have had a significant effect on the atmosphere by making it warmer.

The greenhouse effect is a theory which states that heat is trapped near Earth’s surface by carbon dioxide gas, atmospheric water vapour and some other gases. The heat which is trapped comes from visible sunlight that is able to pass through the atmosphere to Earth’s surface. There it is absorbed. The heated surface emits infrared radiation (heat) into the atmosphere where carbon dioxide and water vapour absorbs and re emits it back towards Earth. This prevents heat from escaping which in turn leads to increasing temperatures. (Global warming)



Our increased burning of fossil fuels in vehicles, furnaces and industry is widely to blame for the increasing amounts of carbon dioxide in the atmosphere. Average global temperatures have also been on the rise. Many scientists believe these two phenomena are linked. The extra carbon dioxide in the atmosphere is like an extra blanket on your bed, causing the temperature to rise. Continued emission of carbon dioxide at the same rate may lead to continued global warming and dramatic climate changes.

Global WarmingThe chemical products of the combustion of hydrocarbons can be variable. With sufficient oxygen present the combustion of hydrocarbons such as methane produces carbon dioxide and water vapour. These gases are the two most important greenhouse gases. They absorb heat radiation from Earth and then re-emit it back towards us. An important current issue is the concern about an enhanced greenhouse effect in which additional carbon dioxide and other greenhouse gases such as methane accumulate in the atmosphere and increase the heating effect. The resulting increase in average global temperature is called global warming. Global warming is considered by many scientists to be the most crucial environmental problem in the world today. The increase in CO2 concentration is largely due to the combustion of fossil fuels such as coal, oil, and natural gas. Temperature increases of only a few degrees can cause a melting of polar ice caps, a rise in sea levels, and significant climate change. The following diagram shows projected temperature changes around the word.



Although the rate and extent of global warming is difficult to predict, it seems reasonable to reduce the production of greenhouse gases to avoid any long term damage to our biosphere. We can practice energy conservation, and use energy sources that do not produce carbon dioxide such as solar power, wind power, fuel cells, and photovoltaic cells.

Support Questions

5. How might Canada be affected if global warming becomes significant?



Key Question #7

1.

Take a Stand: Global Warming

Background: As Canada tries to meet government regulations to control the emission of carbon dioxide and other greenhouse gasses, we must consider how we as individuals impact our environment. Technological fixes are not the only answer. Changes in our lifestyles can have a huge impact on how efficiently we use energy. The following technologies are recommended as a means of reducing the production of greenhouse gasses.

More fuel efficient cars High efficiency natural gas furnaces Improved insulation in buildings Improved mass transportation Home energy saving technologies such as set back thermostats

Research: Use library and internet resources to collect information about one of the technologies listed above.

Evaluation:

a. Before people will change their lifestyles or switch to a new technology, they have to be convinced that there is a benefit. Identify a target group, and prepare an advertisement in the form of a poster designed to promote the technology you researched. (20 marks)

b. In a separate report (minimum one page) identify your target group, explain why you think your ad will be effective, and summarize any risks and benefits of the technology that you did not include in your ad. (30 marks)



Key Question #7 (continued)

2. Some vehicles use diesel fuel instead of gasoline. Use the internet to investigate the properties of each of these fuels and the products of their combustion. Which fuel poses a greater threat to the environment? Provide your results in the form of a one page research paper. Be sure to include the properties, chemical formula, combustion reaction, and impact to the environment for each fuel. (10 marks)

3. For the Combustion Reaction Thought Lab, write out your answers for the analysis, and evaluation sections. (5 marks)


SCH3U


Lesson 8 – Neutralization Reactions


Lesson 8 – Neutralization Reactions


Use appropriate terminology related to chemical reactions such as neutralization, acidic and basic

Investigate double displacement neutralization reactions by testing the products for the presence of acids or bases

Assess the effectiveness of some applications of chemical reactions that are used to address social,, and environmental needs and problems

Predict the products of double displacement neutralization reactions Plan and conduct an inquiry to compare the properties of non metal oxide solutions

and metal oxide solutions Investigate neutralization reactions Explain the chemical reactions that result in the formation of acids and bases from

metal oxides and non metal oxides

Introduction

Acid indigestion, antacid remedies, pH balanced shampoos all of these everyday things refer to acids, or acidity. Many people think that all acids are corrosive and dangerous. How can this be if boric acid is often used as an eye wash. Can acids really be as dangerous as people think they are?

The media doesn’t help provide an understanding of what acids and bases are, or what they do. In fact they usually accentuate only one idea such as the environmental damage caused by acid rain, or the cleaning power of a base. A consumer can get confused, take for instance buying fertilizer. We know the media says that acidic rain kills plants and trees. Why then do they sell fertilizer for acid loving plants such as evergreens?In this lesson we will look at how acids and bases combine to produce neutral products.

Acids and Bases

For thousands of years people have known that vinegar, lemon juice and many other foods taste sour. However, it was not until a few hundred years ago that it was discovered why these things taste sour, it is because they are all acids.

In the seventeenth century, Robert Boyle first labelled substances as either acids or bases according to the following characteristics: Acids taste sour, are corrosive to metals, change litmus paper red, and become less acidic when mixed with bases. Bases feel slippery, change litmus paper blue, and become less basic when mixed with acids. In the late 1800s, the Swedish scientist Svante Arrhenius proposed that water can dissolve many compounds by separating them into their individual ions. Arrhenius


http://www.visionlearning.com/library/pop_glossary_term.php?oid=853&l=


http://www.visionlearning.com/library/module_viewer.php?mid=57#solvent





suggested that acids are compounds that contain hydrogen and can dissolve in water to release hydrogen ions into solution. The following equation shows the dissociation of HCl in water to form hydrogen ions (indicates HCl is an acid) and chloride ions.

HCl H+ + Cl-

Arrhenius defined bases as substances that dissolve in water to release hydroxide ions (OH) into solution. The following equation shows the dissociation of sodium hydroxide in water to form sodium ions and hydroxide ions (indicates NaOH is a base).

NaOH Na+ + OH-

The Arrhenius definition of acids and bases explains a number of things. It explains that all acids have similar properties because they release H+ into solution. The same can be said for bases. All bases have similar properties because they release OH- into solution. This being said, it is easy to understand that acids and bases counteract each other. This idea, that a base can make an acid weaker, and vice versa, is called neutralization.

Summary of the properties of acids and bases

Acids BasesTaste Sour

household vinegar (acetic acid) lemon juice, orange juice or citrus fruit

juices (citric acid) Vitamin C (ascorbic acid) Coca-Cola (contains phosphoric acid)

Bitter Milk of Magnesia (magnesium

hydroxide) Maalox antacid

(Magnesium hydroxide and aluminum hydroxide)

Feel bases often feel slippery or soapy;

Reaction to Litmus Paper

turn litmus paper red turn litmus paper blue

Reactions React with bases to form salt and water (i.e. neutralization reaction)

React with metals such as magnesium, zinc, iron to produce hydrogen gas, H2 (g).

React with acids to form salt and water (i.e. neutralization reaction)

Examples car battery (sulphuric acid) stomach acid (hydrochloric acid) carbonate water (carbonic acid)

drain cleaner, oven cleaner (sodium hydroxide)

cleaning products (ammonia solution)


http://nobel.scas.bcit.ca/0010/i-m.htm#litmus










pHSkin care and hair care products are often advertised as being pH balanced. pH is a way of indicating the concentration of H+ ions present in a solution. We now know that all acids release H+ ions when they dissociate in water, meaning pH measures how acidic a solution is. Every solution contains H+ and OH- ions. You might think that a glass of neutral water contains no H+ but it does. Even pure water contains tiny amounts of both hydrogen ions, and hydroxide ions. The more hydrogen ions a solution has the more acidic it is. The more hydroxide ions there are, the more basic the solution. Neutral solutions have equal numbers of H+ ions and OH- ions.

H2O H+ + OH-

The pH of pure water is 7, this is neutral. Any solution with a pH below 7 is an acid and any solution with a pH above 7 is a base.

Lab: Making a pH Indicator

Purpose: To create a solution which when added to a compound will change colour indicating whether it is an acid or a base.

Materials: red cabbageknifepot or sauce panwaterstovefilter paper (coffee filter, or a strainer)

Procedure: Chop the cabbage into small pieces until you have about two cups. Place the cabbage into a pot and cover with water. Boil this mixture for at least 10 minutes. This will allow the colour to be extracted from within the cabbage.



Separate the cabbage from the red-purple liquid. This liquid is pH 7, and will be used as an indicator.

Support Questions

1. For each of the following solutions, determine whether they are acidic or basic. Don’t forget to include your reasoning.

a. H2SO4

b. NaOHc. HNO3

d. Mg(OH)2

Acidic and Basic Solutions

The combustion of metals and non-metals, produces products which are either acidic or basic.

When metals combine with oxygen in a combustion reaction their products are basic. The following example shows that MgO2 produced in the combustion reaction is basic.

Metal + oxygenmetal oxide (basic)

Mg + O2 MgO2

When non-metals combine with oxygen in a combustion reaction their products are acidic. The following example shows that SO2 produced in the combustion reaction is acidic.

Nonmetal + oxygen nonmetal oxide

S + O2 SO2

Acid RainRain is normally slightly acidic due to the presence of carbon dioxide, which dissolves in atmospheric moisture and reacts to form very dilute carbonic acid. Nitrogen oxides from lightning strikes, and plant decay, and sulphur oxides from volcanic eruptions also contribute to the natural acidity of rain. The combustion of non-metals contributes to the acidity of rain. They produce nitric and sulphuric acid in reactions with atmospheric water.

Human activity has considerably increased the amount of oxides being released into the atmosphere. Our every day activities involve a great number of combustion reactions from riding the bus to heating our homes. Gaseous oxides of nitrogen such as nitrogen



monoxide, and nitrogen dioxide, and sulphur such as sulphur dioxide and sulphur trioxide are released from sources such as automobiles and coal burning power plants.

These oxides join the naturally produced oxides in the atmosphere, react with water vapour to form acids, and are responsible for the increased acidity of precipitation known as acid rain. Acid rain is any form of natural precipitation that has an abnormally high acidity.

Support Questions

1. For each of the following solutions, determine whether they are acidic or basic. Don’t forget to include your reasoning.

a. SO3 b. CaO2 c. NO

2. Sulphur trioxide is a by product of the combustion of gasoline in car engines. In the atmosphere it reacts with condensed water on dust particles producing sulphuric acid. Write out the balanced chemical equation for this reaction. Indicate whether the products are acidic, basic, or neutral.



Neutralization ReactionsAn acid can react with a base in a double displacement reaction called neutralization. A neutralization reaction is a double displacement reaction between an acid and a base to produce an ionic compound such as a salt and water. In this type of reaction the products formed are neither acidic nor basic. The following reaction between magnesium hydroxide (a base) and hydrochloric acid ( an acid) is an example of this type of double displacement neutralization reaction.

Mg(OH)2(s) + 2 HCl(aq) MgCl2(aq) + 2 H2O(l)

From our knowledge of acids and bases we know that acids release H+ into solution, and bases release OH-. If we were to mix an acid and base together, the H+ would combine with the OH- to make a water molecule H2O.

H+ + OH- H2O

The neutralization reaction of an acid and a base will always produce water and a salt as shown by the equation below. .

Acid + Base H2O + Salt

Practice writing out a neutralization reaction!

Write the balanced chemical equation for the reaction of hydrochloric acid with sodium hydroxide.

Step 1: Write out the chemical equation for this reaction

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

Step 2: Balance your reaction.

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

The balanced chemical equation for this question is: HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)



Support Questions

3. Predict the products for the following reaction. Write a balanced chemical equation to represent the reaction.

NaOH(aq) + H2SO4(aq)

Lab: Neutralization Reactions

Purpose: How does an antacid neutralize stomach acid?

Hypothesis: Write out the double displacement reaction for the antacid, and acid of your choice. Be sure to include a balanced chemical equation. Using your knowledge from this unit, and your reaction, predict the pH of the products (acidic, basic or neutral)

Materials: Red cabbage indicatorAcid solution (vinegar, lemon juice etc)Antacid (baking soda, tums, milk of magnesia etc)

Procedure: 1. Measure out 10 mL of your acid (vinegar etc)2. Add 30 - 40 drops of your pre made red cabbage indicator3. Record the colour of the initial solution4. Add a spoonful of your antacid to the container that has both the

acid, and indicator. (If you are using tablet antacids, be sure to crush them into powder form first)

5. Stir well6. Record any observations that may be important such as colour

change

Observations: Create an observation table that includes all quantitative and qualitative observations that you made.

Analysis: 1. What products were formed as a result of the neutralization reaction? What observations provide evidence to support your answers?

2. Express the reaction observed in this investigation in the form of a word equation.

3. 3. Write a balanced chemical equation for the reaction observed.



Evaluation: 1. What types of safety precautions were followed during this experiment? Suggest an improvement to this experiment that would allow you to be more certain about the reaction.

2. Are there any discrepancies between your observations/results, and hypothesis? If so, explain why this might be.

Conclusion: Explain how antacids neutralize stomach acid. Be sure to include your results as evidence.

Key Question #8

1.Take a Stand: Power Plant Scrubbers

Background: Power plants are presently in the process of changing how they produce energy. There currently is a shift from oil to burning coal to power these large plants. With the increase in this technology more non metal oxides such as nitrogen monoxide, and sulphur dioxide will be released into the atmosphere. To counteract this environmental problem, scrubbers have been introduced. They are supposed to help control the increased amount of sulphur dioxide air pollution that is being produced from power plants.

Research: Use library and internet resources to collect information about scrubbers

Evaluation: Before power plants will switch to a new technology, they have to be convinced that there is a benefit. Prepare a pamphlet targeted to the industrial sector designed to promote installing scrubber systems in their plants. (20 marks)

2. For the neutralization reaction lab write out a formal lab report including a title page, purpose, hypothesis, materials, procedure, observations, analysis, evaluation and conclusion section. Be sure to answer any questions present in the lab. (15 marks)


SCH3U


Support Question Answers

SCH3U – Chemistry Support Question Answers

Lesson 5

1. This is a chemical change, since bubbles form. The bubbles indicate a gas was produced.

2. Gas produced: In baking, the baking soda causes carbon dioxide to form which allows baked goods to rise

Light produced: Striking a match

Change in smell: Souring of milk

Colour change: The ripening of a tomato

3. This reaction does not follow the law since there is an extra NO3 on the products side.

4. a. 2 Al(s) + 3 F2(g) 2 AlF3 synthesis reaction

b. 2 KCl(s) 2 K + Cl2 decomposition

5. a. _4__Fe + __3_O2 __2_Fe2O3

b. _1__P4 + __6 _Cl2 _4__PCl3

6. a. 2 CuO 2 Cu + O2 decomposition

b. Cu + Cl2 CuCl2 synthesis

Lesson 6

1. a. Pb(s) + 2 HCl(aq) PbCl2 + H2

b. Ca(s) + 2 H2O(l) Ca(OH)2 + H2

c. Sn(s) + 2 AgNO3(aq Sn(NO3)2 + 2 Ag

d. 2 Al(s) + 3 ZnSO4(aq) Al2(SO4)3 + 3 Zn

2. An element and a compound react to produce a single displacement reaction.

3. a. KNO3 (aq)

b. Al(SO4) (aq)

c. (NH4)2CO3 (aq)


SCH3U – Chemistry Support Question Answers

4. a. single displacementb. double displacement

5. a. 2 CuNO3(aq) + MgCl2(aq) Mg(NO3)2(aq) + 2 CuCl(aq)

b. 3 Ba(OH)2(aq) + Fe2(SO4)3(aq) 2 Fe(OH)3(s) + 3 BaSO4(s)

c. (NH4)2S (aq) + FeSO4 (aq) FeS (s) + (NH4)2SO4(aq)

Lesson 7

1. a. Any potential sparks could lead to a fire or explosion.b. The type of reaction that could occur is a combustion reaction. c. A spark, or heat is required, as well as oxygen, and fuel.

2. 2 C14H30 + 43 O2 28 CO2 + 30 H2O

3. Complete combustion produces carbon dioxide and water, where incomplete combustion produces carbon, carbon monoxide, carbon dioxide, and water.

4. a. C7H16 + 11 O2 7 CO2 + 8 H2O

b. 4 C7H16 + 37 O2 14 CO + 14 CO2 + 32 H2O

5. Canada would no longer have 4 seasons. The snowfall we get in the winter would be drastically reduced. Temperatures would be abnormally high allowing different types of crops/produce to now be grown i.e., citrus. Another change could be caused by the potential for the ice caps to melt. If melting occurs, Canada could see a large part of itself underwater.

Lesson 9

1. a. acidic, produces H+

b. basic, produces OH-

c. acidic, produces H+

d. basic, produces OH-

2. a. acidic, since S is a non metal, and when non metals combine with O they produce acidic oxides.

b. basic, since Ca is a metal, and when metals combine with O they produce basic oxides.

c. acidic, since N is a nonmetal

3. SO3 + H2O H2SO4 This reaction produces an acidic product.

4. 2 NaOH(aq) + H2SO4(aq) Na2SO4 + 2 H2O


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