Chemical Change & Rate of Reaction (Cambridge (CIE) IGCSE Chemistry)

Exam Questions

10 hours71 questions
1a2 marks

An organic compound decomposes to form nitrogen.

C6H5N2Cl(aq) → C6H5Cl(l) + N2(g)

Explain the state symbols.

aq

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

l

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

g

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

1b2 marks

Draw a diagram to show the arrangement of the outer electrons in one molecule of nitrogen.

1c6 marks

The rate of this reaction can be measured using the following apparatus.

rate-of-reaction-volume-of-gas

The results of this experiment are shown on the graph below.

 

volume-of-rates-graph-

i) How does the rate of this reaction vary with time?

[1]

ii) Why does the rate vary?

[2]

iii) The reaction is catalysed by copper powder. Sketch the graph for the catalysed reaction on the same grid.

[2]

iv) Why is copper powder more effective as a catalyst than a single piece of copper?

[1]

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2a3 marks

Biological catalysts produced by microbes cause food to deteriorate and decay. 

i) What is the name of these biological catalysts?

[1]

ii) Freezing does not kill the microbes. Suggest why freezing is still a very effective way of preserving food.

[2]

2b3 marks

Describe how the pea plant makes a sugar such as glucose.

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3a1 mark

A student investigates the reaction of small pieces of zinc with dilute sulfuric acid at 20 °C. The zinc is in excess.

The graph shows the volume of hydrogen gas released as the reaction proceeds.  

q4a_specimen-paper-0620-03-cie-igcse-chemistry

Suggest why the volume of hydrogen gas stays the same after 10 minutes.

3b1 mark

Deduce the time taken from the start of the experiment to collect 20 cm3 of hydrogen gas.

3c2 marks

The student repeats the experiment at 30 °C.

All other conditions stay the same.

Draw a line on the grid in part (a) to show how the volume of hydrogen gas changes with time when the reaction is carried out at 30 °C.

3d2 marks

The student repeats the experiment using zinc powder instead of small pieces of zinc.

Describe how the rate of reaction differs when zinc powder is used.

Give a reason for your answer.

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4a1 mark

Acids have characteristic properties.

The rate of reaction of iron with sulfuric acid can be determined by measuring the time taken to produce 20cm3 of hydrogen.

A student measured the time taken to produce 20 cm3 of hydrogen using three different concentrations of sulfuric acid.

In each experiment the student used:

  • 1g of iron powder

  • the same temperature

  • the same volume of sulfuric acid.

The results are shown in the table. 

concentration of acid in mol / dm3

time / s

0.1

33

0.2

17

0.5

8

Use the information in the table to describe how the rate of reaction changes with the concentration of sulfuric acid.

4b2 marks

Describe the effect of each of the following on the rate of this reaction with 0.5 mol / dm3 of sulfuric acid.

  • Larger pieces of iron are used. All other conditions stay the same. ...................................................................................................................  

  • The temperature is increased. All other conditions stay the same. ...................................................................................................................

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51 mark

Sulfur dioxide is a pollutant in the air.

Sulfur dioxide is oxidised to sulfur trioxide in the air. Oxides of nitrogen act as catalysts for this reaction.

What is meant by the term catalyst?

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6a1 mark

A student investigates the rate of reaction of large pieces of magnesium carbonate with an excess of dilute nitric acid.

MgCO3 + 2HNO3 → Mg(NO3)2 + CO2 + H2O

Name the salt formed when magnesium carbonate reacts with dilute nitric acid.

6b1 mark

The graph shows how the volume of carbon dioxide changes with time.

q7b-0620_s19_qp_33

After how many seconds did the reaction finish?

6c1 mark

From the graph, deduce the volume of carbon dioxide produced during the first 50 seconds of the experiment.

6d2 marks

The experiment is repeated using smaller pieces of the same mass of magnesium carbonate.

All other conditions are kept the same.

Draw a line on the grid for the experiment using smaller pieces of magnesium carbonate.

6e1 mark

How does increasing the temperature affect the rate of this reaction?
All other conditions are kept the same.

6f1 mark

How does decreasing the concentration of nitric acid affect the rate of this reaction?
All other conditions are kept the same.

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1a6 marks

Separate: Chemistry and Extended Only

A length of magnesium ribbon was added to 50 cm3 of sulfuric acid, concentration 1.0 mol/dm3. The time taken for the magnesium to react was measured. The experiment was repeated with the same volume of different acids. In all these experiments, the acid was in excess and the same length of magnesium ribbon was used.

Experiment

Acid 

Concentration in mol/dm3

Time / s

A

sulfuric acid

1.0 

20

B

propanoic acid

0.5

230

C

hydrochloric acid

1.0

40

D

hydrochloric acid

0.5

80

i) Write these experiments in order of reaction speed. Give the experiment with the fastest speed first.

[1]

ii) Give reasons for the order you have given in (i).

[5]

1b5 marks

Suggest two changes to experiment C which would increase the speed of the reaction and explain why the speed would increase. The volume of the acid, the concentration of the acid and the mass of magnesium used were kept the same.

change 1 ....................................................................................................

explanation ................................................................................................

change 2 ....................................................................................................

explanation .................................................................................................

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2a3 marks

Manganese is a transition element. It has more than one valency and the metal and its compounds are catalysts.

Predict three other properties of manganese that are typical of transition elements.

2b3 marks

Extended Only

It has several oxides, three of which are shown below. Manganese(II) oxide, which is basic. Manganese(III) oxide, which is amphoteric. Manganese(IV) oxide, which is acidic.

i) Complete the word equation.

manganese(II) oxide + hydrochloric acid → .....................  ..................... + .....................

[2]

ii) Which, if any, of these oxides will react with sodium hydroxide?

[1]

2c7 marks

Aqueous hydrogen peroxide decomposes to form water and oxygen.

2H2O2 (aq) → 2H2O (l) + O2 (g)

This reaction is catalysed by manganese(IV) oxide. The following experiments were carried out to investigate the rate of this reaction. A 0.1 g sample of manganese(IV) oxide was added to 20 cm3 of 0.2 mol / dm3 hydrogen peroxide solution. The volume of oxygen produced was measured every minute. The results of this experiment are shown on the graph.

graph-o2-vs-time

i) How does the rate of reaction vary with time? Explain why the rate varies.

[3]

ii) The following experiment was carried out at the same temperature. 0.1 g of manganese(IV) oxide and 20 cm3 of 0.4 mol / dm3 hydrogen peroxide. Sketch the curve for this experiment on the same grid.

[2]

iii) How would the shape of the graph differ if only half the mass of catalyst had been used in these experiments?

[2]

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3a
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6 marks

The equation for the reaction between sodium thiosulfate and hydrochloric acid is given below.

Na2S2O3 (aq) + 2HCl (aq) → 2NaCl (aq) + S (s) + SO2 (g) + H2O (l)

The speed of this reaction was investigated using the following experiment. A beaker containing 50 cm3 of 0.2 mol/dm3 sodium thiosulfate was placed on a black cross.

5.0 cm3 of 2.0 mol/dm3 hydrochloric acid was added and the clock was started.

cie-igcse-sq-6-1-cross-reaction

Initially, the cross was clearly visible. When the solution became cloudy and the cross could no longer be seen, the clock was stopped and the time recorded.

The experiment was repeated with 25 cm3 of 0.2 mol/dm3 sodium thiosulfate and 25 cm3 of water. Typical results for this experiment and a further two experiments are given in the table.

thiosulfate-table

 

i) Explain why it is necessary to keep the total volume the same in all the experiments.

[2]

ii) Complete the table.

[1]

iii) How and why does the speed of the reaction vary from experiment 1 to 4?

[3]

3b4 marks

Extended Only

The idea of collisions between reacting particles is used to explain changes in the speed of reactions. Use this idea to explain the following results.

cie-igcse-sq-6-1-cross-reaction-results-2-

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4a7 marks

The rate of the reaction between iron and aqueous bromine can be investigated using the apparatus shown below.

cie-igcse-sq-6-1-mass-reaction-diagram-

A piece of iron was weighed and placed in the apparatus. It was removed at regular intervals and the clock was paused. The piece of iron was washed, dried, weighed and replaced. The clock was restarted.
This was continued until the solution was colourless.
The mass of iron was plotted against time. The graph shows the results obtained.

cie-igcse-sq-6-1-mass-reaction-graph

i) Suggest an explanation for the shape of the graph.

[3]

ii) Predict the shape of the graph if a similar piece of iron with a much rougher surface had been used. Explain your answer.

[2]

iii) Describe how you could find out if the rate of this reaction depended on the speed of stirring.

[2]

4b3 marks

Extended Only

Iron has two oxidation states +2 and +3. There are two possible equations for the redox reaction between iron and bromine.

Fe + Br2 → Fe2+ + 2Br 2Fe + 3Br2 → 2Fe3+ + 6Br

i) Indicate, on the first equation, the change which is oxidation. Give a reason for your choice.

[2]

ii) Which substance in the first equation is the reductant (reducing agent)?

[1]

4c3 marks

Describe how you could test the solution to find out which ion, Fe2+ or Fe3+, is present.

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5a
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6 marks

Some of the factors that can determine the rate of a reaction are concentration, temperature and light intensity.

A small piece of calcium carbonate was added to an excess of hydrochloric acid. The time taken for the carbonate to react completely was measured. 

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l) 

The experiment was repeated at the same temperature, using pieces of calcium carbonate of the same size but with acid of a different concentration. In all the experiments an excess of acid was used. 

concentration of acid in mol / dm3

4

2

2

..........

number of pieces of carbonate

1

1

2

1

time in s

..........

80

..........

160

 i) Complete the table (assume the rate is proportional to both the acid concentration and the number of pieces of calcium carbonate).

 [3]

 ii) Explain why the reaction rate would increase if the temperature was increased.

 [2]

 iii) Explain why the rate of this reaction increases if the piece of carbonate is crushed to a powder.

[1]

5b3 marks

Sodium chlorate(I) decomposes to form oxygen and sodium chloride. This is an example of a photochemical reaction. The rate of reaction depends on the intensity of the light. 

2NaClO (aq) → 2NaCl (aq) + O2 (g)

i) Describe how the rate of this reaction could be measured.

 [2]

 ii) How could you show that this reaction is photochemical?

 [1]

5c2 marks

Separate: Chemistry Only

Photosynthesis is another example of a photochemical reaction. Glucose and more complex carbohydrates are made from carbon dioxide and water.

Complete the equation. 

6CO2 + 6H2O → C6H12O6 + ...........

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6a
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2 marks

The decomposition of hydrogen peroxide is catalysed by manganese(IV) oxide.

2H2O2 (aq) → 2H2O (l) + O2 (g)

To 50 cm3 of aqueous hydrogen peroxide, 0.50 g of manganese(IV) oxide was added. The volume of oxygen formed was measured every 20 seconds. The average reaction rate was calculated for each 20 second interval.

cie-igcse-sq-6-1-h-table-q17

Explain how the average reaction rate, 2.4 cm3/s, was calculated for the first 20 seconds.

6b
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1 mark

Complete the table.

6c2 marks

Explain why the average reaction rate decreases with time.

6d6 marks

The experiment was repeated but 1.0 g of manganese(IV) oxide was added.

What effect, if any, would this have on the reaction rate and on the final volume of oxygen?

Give a reason for each answer.

i) Effect on rate.

[1]

ii) Reason

[2]

iii) Effect on final volume of oxygen.

[1]

iv) Reason

[2]

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7a4 marks

The rate of a reaction depends on the concentration of reactants, temperature and possibly a catalyst or light.

A piece of magnesium ribbon was added to 100 cm3 of 1.0 mol/dm3 hydrochloric acid. The hydrogen evolved was collected in a gas syringe and its volume was measured every 30 seconds.

cie-igcse-sq-6-1-mg-practical-

In all the experiments mentioned in this question, the acid was in excess. The results were plotted to give a graph.

cie-igcse-sq-6-1-mg-graph

i) The experiment was repeated. Two pieces of magnesium ribbon were added to 100 cm3 of 1.0 mol/dm3 hydrochloric acid. Sketch this graph on the same grid and label it X.

[2]

ii) The experiment was repeated using one piece of magnesium ribbon and 100 cm3 of 1.0 mol/dm3 ethanoic acid. Describe how the shape of this graph would differ from the one given on the grid.

[2]

7b4 marks

Extended Only

Reaction rate increases when concentration or temperature is increased.

Using the idea of reacting particles, explain why; 

i) Increasing concentration increases the reaction rate,

[2]

ii) Increasing temperature increases reaction rate.

[2]

7c3 marks

Separate: Chemistry Only

The rate of a photochemical reaction is affected by light. A reaction, in plants, between carbon dioxide and water is photochemical. 

i) Name the two products of this reaction.

[2]

ii) This reaction will only occur in the presence of light and another chemical. Name this chemical.

[1]

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8a2 marks

Extended Only

The following apparatus was used to measure the rate of the reaction between zinc and iodine.

cie-igcse-sq-6-1-experiment-zn

The mass of the zinc plate was measured every minute until the reaction was complete.

Write an ionic equation for the redox reaction that occurred between zinc atoms and iodine molecules.

8b3 marks

Describe how you could show by adding aqueous sodium hydroxide and aqueous ammonia that a solution contained zinc ions.

Result with sodium hydroxide .....................................................................................

Excess sodium hydroxide .....................................................................................

Result with aqueous ammonia .....................................................................................

Excess aqueous ammonia .....................................................................................

8c5 marks

From the results of this experiment two graphs were plotted.

cie-igcse-sq-6-1-graphs-19

i) Which reagent iodine or zinc was in excess? Give a reason for your choice.

[1]

ii) Describe how the shape of graph 1 would change if 100 cm3 of 0.05 mol/dm3 iodine had been used.

[2]

iii) On graph 2, sketch the shape if the reaction had been carried out using 100 cm3 of 0.1 mol/dm3 iodine at 35 °C instead of at 25 °C.

[2]

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9a1 mark

A student investigates the progress of the reaction between dilute hydrochloric acid, HCl, and an excess of large pieces of marble, CaCO3, using the apparatus shown in Fig. 5.1.

q5

Fig. 5.1

A graph of the volume of gas produced against time is shown in Fig. 5.2.

q5a

Fig. 5.2

State how the shape of the graph shows that the rate of reaction decreases as the reaction progresses.

9b1 mark

Suggest why the rate of reaction decreases as the reaction progresses.

9c1 mark

Deduce the time at which the reaction finishes.

9d2 marks

The experiment is repeated using the same mass of smaller pieces of marble.
All other conditions are kept the same.
Draw a line on the grid in Fig. 5.2 to show the progress of the reaction using the smaller pieces of marble. 

9e2 marks

Extended Only

The original experiment is repeated at a higher temperature. All other conditions are kept the same. The resulting increase in rate of reaction can be explained in terms of activation energy and collisions between particles.

Define the term activation energy. 

9f3 marks

Extended Only

Explain why the rate of a reaction increases when temperature increases, in terms of activation energy and collisions between particles.

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10a1 mark

Sulfur dioxide, SO2 , is used in the manufacture of sulfuric acid.

Why is a catalyst used?

10b3 marks

Extended Only

Explain, in terms of particles, why a high temperature increases the rate of this reaction.

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11a2 marks

Oxygen is produced by the decomposition of hydrogen peroxide. Manganese(IV) oxide is the catalyst for this reaction.

What is meant by the term catalyst?

11b4 marks


Extended Only

A student measures the volume of oxygen produced at regular time intervals using the apparatus shown. Large lumps of manganese(IV) oxide are used.

q4b-1-0620-s20-qp-42

A graph of the results is shown.

q4b-2-0620-s20-qp-42

What happens to the rate of this reaction as time increases?
In your answer, explain why the rate changes in this way.

11c2 marks

The experiment is repeated using the same mass of manganese(IV) oxide.

Powdered manganese(IV) oxide is used instead of large lumps. All other conditions stay the same.

Sketch a graph on the axes in (b) to show how the volume of oxygen changes with time.

11d3 marks

Extended Only

In terms of particles, explain what happens to the rate of this reaction when the temperature is increased.

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123 marks

Extended Only

Ammonia is manufactured by the Haber process.

Explain, in terms of particles, what happens to the rate of this reaction when the temperature is increased.

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13a1 mark

A student investigates the rate of reaction of small pieces of calcium carbonate with an excess of hydrochloric acid of concentration 1mol/dm3.

CaCO subscript 3 space end subscript open parentheses straight s close parentheses space plus space 2 HCl space open parentheses aq close parentheses rightwards arrow CaCl subscript 2 space end subscript open parentheses aq close parentheses space plus CO subscript 2 space end subscript open parentheses straight g close parentheses space plus straight H subscript 2 straight O space open parentheses straight l close parentheses

Name the salt formed when calcium carbonate reacts with hydrochloric acid.

13b1 mark

The graph shows how the mass of the reaction mixture changes with time.

q7b-0620_s19_qp_31

State why the reaction mixture decreases in mass.

13c
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1 mark

Calculate the loss in mass during the first 40 seconds of the experiment.

13d2 marks

The experiment is repeated using hydrochloric acid of concentration 2 mol/dm3

All other conditions are kept the same.

Draw a line on the grid for the experiment using hydrochloric acid of concentration 2 mol/dm3.

13e
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1 mark

In the experiment, when 2.00 g of calcium carbonate is used, the loss in mass of the reaction mixture is 0.88 g. All other conditions are kept the same.

Calculate the loss in mass when 0.50 g of calcium carbonate is used.

13f1 mark

The experiment is repeated using the same mass of different-sized pieces of calcium carbonate. All other conditions are kept the same. The sizes of the pieces of calcium carbonate are:

  • powder

  • small pieces

  • large pieces.

Complete the table by writing the sizes of the pieces of calcium carbonate in the first column.

size of pieces of calcium carbonate

initial rate of loss in mass in g/ s

 

0.005

 

0.030

 

0.100

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14a2 marks

The graph shows how the volume of hydrogen produced changes with time.

q7b-0620_s19_qp_32

Describe how the rate of reaction changes with time.
Use the graph to explain your answer.

14b1 mark

How many seconds did it take to collect the first 25 cm3 of hydrogen?

14c2 marks

The experiment is repeated at a higher temperature. All other conditions are kept the same.

Draw a line on the grid for the experiment using a higher temperature.

14d
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1 mark

If 2.4 g of magnesium is used, 0.2 g of hydrogen is produced. Calculate the mass of magnesium needed to produce 0.8 g of hydrogen using an excess of dilute hydrochloric acid.

mass of magnesium = .............................. g

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151 mark

Oxides of nitrogen are pollutants in the air.

Oxides of nitrogen act as catalysts.
What is meant by the term catalyst?

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1a4 marks

Hydrogen peroxide decomposes to form water and oxygen. This reaction is catalysed by manganese(IV) oxide.

2H2O2 (aq) → 2H2O (l) + O2 (g)

The rate of this reaction can be investigated using the following apparatus.

cie-igcse-sq-h-6-1-q1a

40 cm3 of aqueous hydrogen peroxide was put in the flask and 0.1 g of small lumps of manganese(IV) oxide was added. The volume of oxygen collected was measured every 30 seconds. The results were plotted to give the graph shown below.

cie-igcse-sq-6-1h-graph-q5a

i) How do the rates at times t1, t2 and t3 differ?

[2]

ii) Explain the trend in reaction rate that you described in a) i).

[2]

1b4 marks

The experiment was repeated using 0.1 g of finely powdered manganese(IV) oxide. All the other variables were kept the same.

i) On the same axes as the graph in part a), sketch the graph that would be expected for this change.

[2]

ii) Explain the shape of this graph.

[2]

1c4 marks

Describe how you could show that the catalyst, manganese(IV) oxide, was not used up in the reaction.

Manganese(IV) oxide is insoluble in water.

1d
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3 marks

In the first experiment, the maximum volume of oxygen produced was 96 cm3 measured at r.t.p.

Calculate the concentration of the aqueous hydrogen peroxide in mol/dmby completing the following steps.

2H2O2 (aq) → 2H2O (l) + O2 (g)

i) Calculate the number of moles of O2 formed

[1]

ii) Calculate the number of moles of H2O2 in 40 cm3 of solution

[1]

iii) Calculate the concentration of the aqueous hydrogen peroxide in mol/dm3

[1]

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2a5 marks

The speed (rate) of a chemical reaction depends on a number of factors, including temperature and the presence of a catalyst.

Reaction speed increases as the temperature increases.

 

i) Explain why reaction speed increases with temperature.

[3]

ii) Reactions involving enzymes do not follow the above pattern.

The following graph shows how the speed of such a reaction varies with temperature.

rsP2-wMk_cie-igcse-sq-6-1-h-enzyme-graph-q2a

Suggest an explanation why initially the reaction speed increases then above a certain temperature the speed decreases.

[2]

2b6 marks

An organic compound decomposes to give off nitrogen. 

C6H5N2Cl (aq) → C6H5Cl (l) + N2 (g)

The speed of this reaction can be determined by measuring the volume of nitrogen formed at regular intervals. Typical results are shown in the graph below.

cie-igcse-sq-6-1-h-graph-q2a

The reaction is catalysed by copper.

i) Sketch the graph for the catalysed reaction on the diagram above.

[2]

ii) How does the speed of this reaction vary with time?

[1]

iii) Why does the speed of reaction vary with time?

[3]

2c7 marks

Catalytic converters reduce the pollution from motor vehicles. 

i) Describe how carbon monoxide and the oxides of nitrogen are formed in car engines. 

[4]

ii) Describe the reaction(s) inside the catalytic converter which change these pollutants into less harmful gases.

Include at least one equation in your description.

[3]

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3a3 marks

Hydrogen peroxide, H2O2, decomposes into water and oxygen in the presence of a catalyst, manganese(IV) oxide.

2H2O2 (aq) → 2H2O (l) + O2 (g)

What is meant by the term catalyst?

3b2 marks

A student studies the rate of decomposition of hydrogen peroxide using the apparatus shown.

The student uses 20 cm3 of 0.1 mol/dm3 hydrogen peroxide and 1.0 g of manganese(IV) oxide.

The student measures the volume of oxygen given off at regular time intervals until the reaction stops. A graph of the results is shown.

h2o2-and-cat-equip-graph

i) When is the rate of reaction highest?

[1]

ii) Suggest one method of increasing the rate of reaction using the same amounts of hydrogen peroxide and manganese(IV) oxide.

[1]

3c
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5 marks

The reaction can be examined quantitatively. 

i) Calculate the number of moles of hydrogen peroxide used in this experiment.

[1]

ii) Use your answer to c) i) and the equation to calculate the number of moles of oxygen produced in the reaction. 

2H2O2 (aq) → 2H2O (l) + O2 (g)

[1]

iii) Calculate the volume (at r.t.p.) of oxygen produced in dm3

[1]

iv) What would be the effect on the volume of oxygen produced if the mass of the catalyst was increased?

[1]

v) Deduce the volume of oxygen, in dm3, that would be produced if 20 cm3 of 0.2 mol/dm3 hydrogen peroxide was used instead of 20 cm3 of 0.1 mol/dm3 hydrogen peroxide

[1]

3d3 marks

The student carries out a second experiment to investigate whether another substance, copper(II) oxide, is a better catalyst than manganese(IV) oxide.

Describe how the second experiment is carried out. You should state clearly how you would make sure that the catalyst is the only variable.

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4a4 marks

The reactions between metals and acids are redox reactions. 

Zn + 2H+ → Zn2+ + H2

i) Which change in the above reaction is oxidation, Zn to Zn2+ or 2H+ to H2? Give a reason for your choice.

[2]

ii) Which reactant in the above reaction is the oxidising agent? Give a reason for your choice.

[2]

4b5 marks

The rate of reaction between a metal and an acid can be investigated using the apparatus shown below.

cie-igcse-sq-6-1-q4b

A piece of zinc foil was added to 50 cm3 of hydrochloric acid, of concentration 2.0 mol/dm3. The acid was in excess. The hydrogen evolved was collected in the gas syringe and its volume was measured every minute.

The results were plotted and labelled as graph 1.

cie-igcse-sq-6-1-graph-q4b

The experiment was repeated to show that the reaction between zinc metal and hydrochloric acid is catalysed by copper.

A small volume of aqueous copper(II) chloride was added to the acid before the zinc was added.

The results of this experiment were plotted on the same grid and labelled as graph 2.

i) Explain why the reaction mixture in the second experiment contains copper metal. Include an equation in your explanation.

[2]

ii) Explain how graph 2 shows that copper catalyses the reaction.

[3]

4c4 marks

If the first experiment was repeated using ethanoic acid, CH3COOH, instead of hydrochloric acid, how and why would the graph be different from graph 1?

4d
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3 marks

Calculate the maximum mass of zinc which will react with 50 cm3 of hydrochloric acid, of concentration 2.0 mol/dm3

Zn + 2HCl → ZnCl2 + H2

Show your working.

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5a8 marks

Sodium chlorate(I) decomposes to form sodium chloride and oxygen. The rate of this reaction is very slow at room temperature provided the sodium chlorate(I) is stored in a dark bottle to prevent exposure to light.

2NaClO → 2NaCl + O2

The rate of this decomposition can be studied using the following experiment.

cie-igcse-sq-6-1-q5a

Sodium chlorate(I) is placed in the flask and 0.2 g of copper(II) oxide is added. This catalyses the decomposition of the sodium chlorate(I) and the volume of oxygen collected is measured every minute. The results are plotted to give a graph of the type shown below.

cie-igcse-sq-6-1-graph-q5a

i) Explain why the gradient (slope) of this graph decreases with time.

[2]

ii) Cobalt(II) oxide is a more efficient catalyst for this reaction than copper(II) oxide.

Sketch, on the grid, the graph for the reaction catalysed by cobalt(II) oxide.

[2]

iii) All other conditions were kept constant.

What can you deduce from the comment that sodium chlorate(I) has to be shielded from light?

[1]

iv) Explain, in terms of collisions between particles, why the initial gradient would be steeper if the experiment was repeated at a higher temperature.

[3]

5b6 marks

The ions present in aqueous sodium chloride are Na+ (aq), Cl (aq), H+(aq) and OH (aq). The electrolysis of concentrated aqueous sodium chloride forms three products. They are hydrogen, chlorine and sodium hydroxide. 

i) Explain how these three products are formed. Give ionic equations for the reactions at the electrodes.

[4]

ii) If the solution of the electrolyte is stirred, chlorine reacts with sodium hydroxide to form sodium chlorate(I), sodium chloride and water. Complete the equation for this reaction.

  Cl2 + ...NaOH → ..................... + ..................... + .....................

[2]

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6a3 marks

20.0 g of small lumps of calcium carbonate and 40 cm3 of hydrochloric acid, concentration 2.0 mol / dm3, were placed in a flask on a top pan balance. The mass of the flask and contents was recorded every minute.

rate-co2-hcl-equipment

The mass of carbon dioxide given off was plotted against time.

graph-rate-vs-time

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O (l) + CO2 (g)

In all the experiments mentioned in this question, the calcium carbonate was in excess.

i) Explain how you could determine the mass of carbon dioxide given off in the first five minutes.

[1]

ii) Explain how the shape of the graph shows where the rate is fastest, where it is slowing down and where the rate is zero.

[2]

6b2 marks

Sketch on the same graph, the line which would have been obtained if 20.0 g of small lumps of calcium carbonate and 80 cm3 of hydrochloric acid, concentration 1.0 mol / dm3, had been used. 

6c4 marks

Explain in terms of collisions between reacting particles each of the following.

i) The reaction rate would be slower if 20.0 g of larger lumps of calcium carbonate and 40 cm3 of hydrochloric acid, concentration 2.0 mol / dm3, were used.

[2]

ii) The reaction rate would be faster if the experiment was carried out at a higher temperature.

[2]

6d
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4 marks

Calculate the maximum mass of carbon dioxide given off when 20.0 g of small lumps of calcium carbonate react with 40 cm3 of hydrochloric acid, concentration 2.0 mol / dm3.

CaCO3 (s) + 2HCl( aq) → CaCl2 (aq) + H2O (l) + CO2 (g)

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7a2 marks

A diagram of the apparatus which could be used to investigate the rate of reaction between magnesium and an excess of an acid is drawn below.

cie-igcse-sq-6-1-inverted-burette-practical

The magnesium kept rising to the surface. In one experiment, this was prevented by twisting the magnesium around a piece of copper. In a second experiment, the magnesium was held down by a plastic net fastened to the beaker.  

i) Suggest a reason why magnesium, which is denser than water, floated to the surface.

[1]

ii) Iron, zinc and copper have similar densities. Why was copper a better choice than iron or zinc to weigh down the magnesium?

[1]

7b2 marks

The only difference between the two experiments was the method used to hold down the magnesium. The results are shown below.

cie-igcse-sq-6-1-inverted-burette-graph

 

i) In which experiment did the magnesium react faster?

[1]

ii) Suggest a reason why the experiment chosen in part i) had the faster rate.

[1]

7c2 marks

The experiment was repeated using 1.0 mol/dm3 propanoic acid instead of 1.0 mol/dm3 hydrochloric acid. Propanoic acid is a weak acid. 

i) How would the graph for propanoic acid differ from the graph for hydrochloric acid? 

[1]

ii) How would the graph for propanoic acid be the same as the graph for hydrochloric acid?

[1]

7d4 marks

Give two factors which would alter the rate of this reaction. For each factor explain why it alters the rate.

Factor ............................................................................................................................
Explanation ....................................................................................................................

Factor ............................................................................................................................
Explanation ....................................................................................................................

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8a3 marks

A small piece of marble, CaCO3, was added to 5.0 cm3 of hydrochloric acid, concentration 1.0 mol / dm3, at 25°C. The time taken for the reaction to stop was measured. The experiment was repeated using 5.0 cm3 of different solutions of acids. The acid was in excess in all of the experiments.

Typical results are given in the table.

Experiment

Temperature / oC

Acid solution

Time / min

1

25

hydrochloric acid 1.0 mol / dm3

3

2

25

hydrochloric acid 0.5 mol / dm3

7

3

25

ethanoic acid 1.0 mol / dm3

10

4

15

hydrochloric acid 1.0 mol / dm3

8

i) Explain why it is important that the pieces of marble are the same size and the same shape.

[2]

ii) How would you know when the reaction had stopped?

[1]

8b1 mark

The equation for the reaction in experiment 1 is:

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)

Complete the following ionic equation.

CaCO3 (s) + 2H+ (aq) → ............ + ............ + ............

8c6 marks

i) Explain why the reaction in experiment 1 is faster than the reaction in experiment 2.

[1]

ii) The acids used for experiment 1 and experiment 3 have the same concentration. Explain why experiment 3 is slower than experiment 1.

[2]

iii) Explain in terms of collisions between reacting particles why experiment 4 is slower than experiment 1.

[3]

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9a6 marks

A small piece of marble, calcium carbonate, was added to 5 cm3 of hydrochloric acid at 25 °C. The time taken for the reaction to stop was measured.

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)

Similar experiments were performed always using 5cmof hydrochloric acid.

Experiment

Number of pieces of marble

Concentration of acid in mol / dm3

Temperature / oC

 Time / min

1

1

1.00

25

3

2

1

0.50

25

7

3

1 piece crushed

1.00

25

1

4

1

1.00

35

2

Explain each of the following in terms of collisions between reacting particles.

i) Why is the rate in experiment 2 slower than in experiment 1?

[2]

ii) Why is the rate in experiment 3 faster than in experiment 1?

[2]

iii) Why is the rate in experiment 4 faster than in experiment 1?

[2]

9b
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7 marks

An alternative method of measuring the rate of this reaction would be to measure the volume of carbon dioxide produced at regular intervals.

i) Sketch this graph.

vol-vs-time-graph

[2]

ii) One piece of marble, 0.3 g, was added to 5 cm3 of hydrochloric acid, concentration 1.00 mol / dm3. Which reagent is in excess? Give a reason for your choice.

Mass of one mole of CaCO3 = 100g Number of moles of CaCO3 = Number of moles of HCl = Reagent in excess is: Reason:

[4]

iii) Use your answer to (ii) to calculate the maximum volume of carbon dioxide produced measured at r.t.p.

[1]

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10a5 marks

Many organic compounds which contain a halogen have chloro, bromo or iodo in their name.

The following diagram shows the structure of 1-chloropropane. 

cie-igcse-sq-11-3-1-chloropropane-3a

 i) Draw the structure of an isomer of this compound.

 [1]

 ii) Describe how 1-chloropropane could be made from propane.

 [2]

 iii) Suggest an explanation why the method you have described in (ii) does not produce a pure sample of 1-chloropropane.

 [2]

10b3 marks

Organic halides react with water to form an alcohol and a halide ion. 

CH3–CH2–I + H2O → CH3–CH2–OH + I 

 i) Describe how you could show that the reaction mixture contained an iodide ion.

 [2]

 ii) Name the alcohol formed when 1-chloropropane reacts with water.

 [1]

10c7 marks

The speed (rate) of reaction between an organic halide and water can be measured by the following method.

A mixture of 10 cm3 of aqueous silver nitrate and 10 cmof ethanol is warmed to 60 °C. Drops of the organic halide are added and the time taken for a precipitate to form is measured.

Silver ions react with the halide ions to form a precipitate of the silver halide.

Ag+ (aq) + X (aq) → AgX (s)

Typical results for four experiments, A, B, C and D, are given in the table. 

experiment 

organic halide

number of drops

time / min

A

bromobutane

4

6

B

bromobutane

8

3

C

chlorobutane

4

80

D

iodobutane

4

0.1

 i) Explain why it takes longer to produce a precipitate in experiment A than in B.

 [2]

 ii) How does the order of reactivity of the organic halides compare with the order of reactivity of the halogens?

 [2]

 iii) Explain why the time taken to produce a precipitate would increase if the experiments were repeated at 50 °C.

 [3]

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