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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.
Pages 190–191 in the Student Book provide a student-friendly checklist for revision.
When and how to use these pages
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.
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.
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
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
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
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
� 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 ‘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?
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).
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?
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.
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?
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,
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.
In this lesson students are learning to:
� 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
Obstacles to learning
The number of possible combinations of acids and salts make it difficult for some students to recall all the formulas
required by the specification.
Stimuli and starter suggestions
� 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.
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.
� 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.
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.
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.
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
C6.2.1 identify the stages in a given chemical synthesis of an inorganic compound (limited to acid–alkali
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.
In this lesson students are learning to:
� 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
Obstacles to learning
Some students will have difficulty handling the ratios of reacting quantities.
Stimuli and starter suggestions
� 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
� 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.
Equipment and materials
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?
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.
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.
Student Book pages 172−173 � Interactive Book: Matching pairs ‘Planning and carrying out a synthesis’; Quick starter ‘Performing a titration’ � Homework pack c6_05
Files on Teacher Pack CD: c6_05_practical; c6_05_technician
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.
In this lesson students are learning to:
� 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
Obstacles to learning
Carrying out titrations requires considerable manual dexterity and coordination. Students need time to become
familiar with handling the apparatus and to build up skills.
Stimuli and starter suggestions
� 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
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)
� 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.
� 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
Files on Teacher Pack CD: c6_06_worksheet; c6_06_practical; c6_06_technician
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
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: Explaining ideas about acidity.
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.
In this lesson students are learning to:
� 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
Obstacles to learning
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.
Stimuli and starter suggestions
� 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.
� 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.
Equipment and materials
beakers • conical flask • pipette and filler • 100 cm3 volumetric flask • burette and stand
• small funnel • white tile • spatula • weighing boat • access to a balance
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:
� 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.
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:
Student Book pages 176−177 � Interactive Book: Naked Scientist animation ‘What are catalysts?’; Practical investigations ‘Weak and strong’ � Homework pack c6_07
Files on Teacher Pack CD: c6_07_worksheet; c6_07_practical; c6_07_technician
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.
C6.2.1 identify the stages in a given chemical synthesis of an inorganic compound (limited to acid–alkali
reactions), including: d. carrying out the reaction in suitable apparatus in the right conditions (such as temperature)
Numeracy focus: Carrying out calculations using experimental data, including finding the mean and the range.
ICT focus: Using sensors and dataloggers.
In this lesson students are learning to:
� 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
Obstacles to learning
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.
Stimuli and starter suggestions
� 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.
� 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.
Equipment and materials
polystyrene cups • measuring cylinder • stirring rod
• thermometer (or temperature sensor and datalogger)
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.
� hand-warmers and self-heating cans; cold packs and coolers for picnic bags
Practical
Each group of students will need:
� 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.
� 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.
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.
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.
Stimuli and starter suggestions
� 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
� use filtering and evaporating to purify a sample of salt.
Remember that apparatus that has been heated can stay hot for a long time.
Equipment and materials
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.
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)
Each group of students will need:
� 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)
Each group of students will need:
� beaker and stirring rod
� filter funnel and paper
� evaporating dish
� 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 ‘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.
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.
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?
� 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.
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.
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.
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.
� 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.
� Magnesium ribbon is FLAMMABLE.
� 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.
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.
In this lesson students are learning to:
� 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
Obstacles to learning
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.
Stimuli and starter suggestions
� 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.
P Investigating factors that change the rate of reactions
Objectives
In this activity you will:
� 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.
• 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.
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.
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.
� Magnesium ribbon is FLAMMABLE.
� 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.
Files on Teacher Pack CD: c6_11_worksheet; c6_11_practical; c6_11_technician
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
C6.2.1 identify the stages in a given chemical synthesis of an inorganic compound (limited to acid–alkali
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.
In this lesson students are learning to:
� understand how catalysts can speed up reactions
� interpret information about controlling rates of reaction
Key vocabulary
catalyst ���� catalytic converter
Obstacles to learning
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.
Stimuli and starter suggestions
� 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.
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.
Worksheet answers Activity 1 (Low demand)
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
Activity 2 (Standard demand)
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.
Activity 3 (High demand)
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.
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.
Equipment and materials
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?
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.’
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.
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.
� 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.
‘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.
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?
6 Design a presentation or prepare a report describing the work you have done on your product.
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.
5 Design a presentation or prepare a report describing the work you have done on your product.