Rates of Reaction (Edexcel IGCSE Chemistry: Double Science)

Exam Questions

2 hours18 questions

1a1 mark

The copper(II) carbonate in the mineral, malachite, reacts with hydrochloric acid according to this equation.

CuCO₃(s) + 2HCl (aq) → CuCl₂ (aq) + H₂O (g) + CO₂ (g)

Some students investigate the effect of changing the concentration of acid on the rate of this reaction. The diagram shows the apparatus they use.

screen-shot-2022-10-10-at-17-50-46

This is the method they use:

set the balance to zero
add an excess of malachite lumps to the conical flask and replace the cotton wool
start a timer and record the balance reading after one minute

The experiment is repeated using different concentrations of hydrochloric acid. The mass and number of malachite lumps are kept the same in each experiment.

The table shows the results obtained in one series of experiments.

screen-shot-2022-10-10-at-19-35-37

State why the balance readings have negative values.

[1]

How did you do?

1b2 marks

The graph shows the results of this series of experiments.

The circled point indicates an anomalous result.

Suggest one mistake the students could have made to produce this result.

[1]

ii)

State the relationship shown by the graph.

[1]

How did you do?

1c2 marks

Explain why an increase in the concentration of the acid causes an increase in the rate of the reaction. You should use the particle collision theory in your answer.

[2]

How did you do?

Did this page help you?

2a1 mark

Dilute hydrochloric acid reacts with a solution of sodium thiosulfate (Na₂S₂O₃) to form a precipitate.

The equation for the reaction is

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

State the name of the precipitate that forms.

(1)

How did you do?

2b2 marks

The reaction is often used to investigate rates of reaction.

The diagram shows the apparatus a student uses to investigate the effect of temperature on the rate of the reaction.

This is the student’s method.

Pour 50 cm³ of cold sodium thiosulfate solution into a conical flask and heat it to 20 °C
Draw a cross (X) on a piece of paper and place it under the flask
Add 5 cm³ of dilute hydrochloric acid to the flask
Look at the cross from above and record the time taken until the cross cannot be seen

The student repeats the experiment four times, using sodium thiosulfate solution at a different temperature each time.

He keeps the volumes of sodium thiosulfate solution and hydrochloric acid constant in each experiment.

Give two other factors that the student should keep constant.

(2)

1 ....................................................................................................

2 ....................................................................................................

How did you do?

2c1 mark

The table shows the student’s results.

Temperature in °C	Time until cross cannot be seen in s
20	400
30	188
40	84
50	44
60	24

The highest temperature the student uses is 60 °C because he thinks the results might not be as accurate at temperatures higher than 60 °C.

Suggest a reason why the results might not be as accurate at temperatures higher than 60 °C.

(1)

How did you do?

2d2 marks

The student wants to compare the rates of the reaction at the different temperatures.

He uses this formula to obtain a value for each rate of reaction

rate =

\frac{1}{time in s}

The table shows the value of the rate of reaction at each temperature.

Temperature in °C	Time until cross cannot be seen in s	Rate of reaction in s^-1
20	400	0.0025
30	188	0.0053
40	84	0.012
50	44	0.023
60	24	0.042

Plot the values of temperature and rate of reaction on the grid.

Draw a curve of best fit through the points.

(2)

How did you do?

5 marks

e) i)

Use the graph to determine a value for the rate of the reaction at 45 °C.

Show on the graph how you obtained your answer.

(2)

rate of reaction = .............................................................. s⁻¹

ii)

Calculate the time that it would take for the cross not to be seen at 45 °C.

(2)

time = .............................................................. s

iii)

Describe the relationship between rate of reaction and temperature shown by the graph.

(1)

How did you do?

2f3 marks

Explain, in terms of particle collision theory, the effect that increasing the temperature has on the rate of a reaction.

(3)

How did you do?

Did this page help you?

4a4 marks

This question is about reactions that form gases.

Hydrogen peroxide decomposes to form water and oxygen.

The equation for the reaction is

2H₂O₂ → 2H₂O + O₂

25.0 cm³ of hydrogen peroxide solution are poured into a conical flask and 1.00 g of solid manganese(IV) oxide is added.

Bubbles of oxygen gas are formed.

Give the test for oxygen gas.

(1)

ii)

Describe a method to show that solid manganese(IV) oxide is a catalyst in this reaction and not a reactant.

(3)

How did you do?

4b9 marks

A student uses this apparatus to investigate the rate of the reaction between zinc and an excess of dilute hydrochloric acid.

2021-ja1c-q11b1

This is the student’s method.

pour 50 cm³ of dilute hydrochloric acid into a conical flask
add about 1.2 g of zinc lumps
record the volume of hydrogen gas collected every 30 s until no more hydrogen is collected

The graph shows the student’s results.

2021-ja1c-q11b2

Calculate the mean (average) rate of reaction, in cm³/ s, in the first 120 s.

(2)

mean rate = .............................................................. cm³/ s

ii)

The equation for the reaction between zinc and hydrochloric acid is

Zn (s) + 2HCl (aq) → ZnCl₂ (aq) + H₂(g)

Use this equation and the particle collision theory to explain why the rate of reaction is greatest at the start of the reaction.

(3)

iii)

The student repeats the experiment at a higher temperature but keeps all other conditions the same.

On the grid, draw the curve you would expect to see in this experiment.

(2)

iv)

Explain why the rate of reaction is greater if the same mass of zinc powder is used instead of zinc lumps. All other conditions are kept the same.

(2)

How did you do?

2 marks

In another experiment, the student adds 0.55 g of zinc to a solution containing 2.50 × 10⁻² moles of hydrochloric acid.

Use the equation to show that hydrochloric acid is in excess.

Zn (s) + 2HCl (aq) → ZnCl₂ (aq) + H₂ (g)

[A_r of Zn = 65]

(2)

How did you do?

Did this page help you?

11a1 mark

A student uses this apparatus in an experiment to study the rate of the reaction between zinc and dilute sulfuric acid.

zn-and-h2so4-gas-collection-practical

This is the student’s method.

Add a few zinc granules to a conical flask on a balance
Add 100 cm³ of dilute sulfuric acid to the flask, start a timer and immediately record the mass of the flask and contents
Record the mass of the flask and contents every minute until the mass remains constant

The mass of the flask and contents decreases because hydrogen gas is produced and leaves the flask.

The student uses the mass readings to calculate the total mass of hydrogen produced.

Complete the equation for the reaction by adding the state symbols.

(1)

Zn (................) + H₂SO₄ (................) → ZnSO₄ (................) + H₂ (................)

How did you do?

11b5 marks

The table shows the student’s results.

Time in minutes	Total mass of hydrogen produced in mg
0	0
1	80
2	110
3	130
4	148
5	162
6	165
7	184
8	192
9	198
10	204
11	209
12	214
13	218
14	220
15	220

Plot the student’s results. The first three have been done for you.

(1)

ii)

Draw a circle around the anomalous result.

(1)

iii)

Draw a curve of best fit.

(1)

Hnxkz0VQ_zn-and-h2so4-gas-collection-blank-graph

iv)

Give a possible reason for the anomalous result.

(1)

Determine a more likely value for this result.

(1)

How did you do?

11c3 marks

c) i)

Explain how the shape of the curve shows how the rate of the reaction changes as time increases.

(2)

ii)

At the end of the experiment there is no zinc left in the flask.

Give a conclusion the student could make from this observation.

(1)

How did you do?

11d3 marks

The student does another experiment using

the same amount of similarly sized magnesium granules instead of zinc
the same volume of sulfuric acid, but of a lower concentration

Explain why it is difficult to predict how the rate of reaction in this experiment compares with the rate of reaction in the first experiment.

(3)

How did you do?

11e3 marks

Explain, in terms of particle collision theory, how increasing the temperature affects the rate of a reaction.

(3)

How did you do?

Did this page help you?

1a2 marks

A student uses this apparatus to investigate the rate of reaction between magnesium and an excess of dilute hydrochloric acid.

mg-and-hcl-gas-syringe-experiment

She uses this method.

use a graduated beaker to pour 50 cm³ of dilute hydrochloric acid of concentration 2.00 mol / dm³ into the conical flask
add a piece of magnesium ribbon of mass 0.086 g to the acid and put the bung into the neck of the flask
measure the total volume of gas collected every ten seconds until the reaction stops

The table shows the student's results.

Time in s	Volume of hydrogen in cm³
0	0
10	29
20	52
30	67
40	76
50	81
60	84
70	84
80	84

a) i)

Plot the student's results on the grid.

(1)

ii)

Draw a curve of best fit

(1)

How did you do?

1b4 marks

b) i)

The student repeats the experiment using

0.043 g of magnesium ribbon
50 cm³ of 2.00 mol / dm³ hydrochloric acid

Draw, on the grid in part (a), the curve you would expect in this experiment.

Label this curve Y.

(2)

ii)

The student repeats the experiment again, using

0.086 g of magnesium ribbon
50 cm³ of 2.00 mol / dm³ hydrochloric acid
a slightly higher temperature than the first experiment

Draw, on the grid in part (a), the curve you would expect in this experiment.

Label this curve Z.

(2)

How did you do?

1c1 mark

The expected volume of gas produced in the first experiment is 86 cm³.

Suggest why the volume collected is less than the expected volume.

(1)

How did you do?

1d2 marks

The student uses a graduated beaker to measure the volume of dilute hydrochloric acid.

Explain why it is not necessary to use a measuring cylinder in this experiment.

(2)

How did you do?

1e3 marks

The ionic equation for the reaction between magnesium and hydrochloric acid is

Mg (s) + 2H⁺ (aq) → Mg²⁺ (aq) + H₂ (g)

Use the information in this equation, and the particle collision theory, to explain why the rate of reaction decreases during each of the experiments.

(3)

How did you do?

Did this page help you?

☐	A	The frequency of the collisions between particles decreases
☐	B	The collisions are less energetic
☐	C	The activation energy increases
☐	D	There are fewer particles with the minimum energy to react

☐	A	Burette, beaker, pipette
☐	B	Ruler, thermometer, test tube
☐	C	Measuring cylinder, delivery tube, stopwatch
☐	D	Filter funnel, evaporating basin, Bunsen burner

☐	A	acid particles are moving
☐	B	gas is given off
☐	C	heat energy is produced
☐	D	marble chips are dissolving

☐	A	The mass of the catalyst at the start of the reaction is the same at the end of the reaction
☐	B	Catalysts increase the rate of reaction but do not increase the yield
☐	C	Catalysts are not chemically changed during the course of the reaction
☐	D	Catalysts provide an alternative reaction pathway which has a lower activation energy

☐	A	To prevent carbon dioxide gas from escaping
☐	B	To ensure the mass stays constant throughout the experiment
☐	C	To prevent the acid from leaving the conical flask
☐	D	To prevent oxygen entering the conical flask

Time in minutes	0	2	4	6	8	10	12	14	16
Volume of oxygen / cm³	0	22	38	50	55	69	76	80	80

☐	A	The reaction finishes after 30 seconds
☐	B	The rate of reaction speeds up during the reaction
☐	C	The final volume of gas produced is 60 cm³
☐	D	The concentration of the hydrogen peroxide decreases during the reaction

☐	A	Increase the temperature of the acid
☐	B	Increase the surface area of the pieces of magnesium
☐	C	Increase the concentration of the hydrochloric acid
☐	D	Increase the volume of hydrochloric acid solution used