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GCSEChemistry: Combined ScienceOCR GatewayExam Questions5. Monitoring & Controlling Chemical Reactions5.2 Controlling Reactions

Controlling Reactions (OCR Gateway GCSE Chemistry: Combined Science)

Exam Questions

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5.2 Controlling Reactions

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5.2 Controlling Reactions

1a3 marks

Zinc and dilute sulfuric acid react to make hydrogen.

Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g)

A student measures the rate of this reaction by measuring the loss in mass of the reaction mixture.

She finds that the change in mass is very small and difficult to measure.

Draw a labelled diagram to show a better way of measuring the rate of this reaction.

How did you do?

1b7 marks

The reaction between zinc and dilute sulfuric acid is slow.

The student decides to try and find a catalyst for this reaction.

She tests four possible substances.

Each time she adds 0.5 g of the substance to 1.0 g of zinc and 25 cm3 of dilute sulfuric acid.

Look at her table of results.

Substance added Colour of substance at start Colour of substance at end Relative rate of reaction
no substance     1
calcium sulfate powder white white 1
copper powder pink pink 10
copper(II) sulfate powder blue pink 30
manganese(IV) oxide powder black black 1

i)
It is important to do the reaction with only zinc and dilute sulfuric acid and no substance added.

Explain why.
[1]
ii)
It is important to do all of the reactions with the same concentration of acid.

Explain why.
[1]
iii)
Which of the substances could be a catalyst for the reaction between zinc and dilute sulfuric acid?

Explain your answer.
[2]

iv)
There is not enough evidence to confirm which substance is a catalyst.

Suggest an extra piece of experimental evidence that could be collected to confirm which substance is a catalyst.
[1]
v)
The student does the experiment with copper, zinc and dilute sulfuric acid again.

This time she uses a lump of copper rather than copper powder.

Predict, with reasons, the relative rate of reaction.
[2]

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2a2 marks

Antacid tablets are used to treat indigestion.

A student investigates two different antacid tablets, X and Y. Both tablets, X and Y, contain calcium carbonate, CaCO3.

Calcium carbonate reacts with hydrochloric acid. Calcium chloride, CaCl2, water and carbon dioxide are made.

Write a balanced symbol equation for this reaction.

How did you do?

2b4 marks

The diagram shows the apparatus the student uses.

q18b-paper-2-june-2018-ocr-gcse-chem

The student reacts tablet X with 100 cm3 of hydrochloric acid. The hydrochloric acid is in excess.

He measures the volume of gas made every minute during the first five minutes.

He does a second experiment using tablet Y and a fresh 100 cm3 sample of the same hydrochloric acid.

The table shows his results.

Time
(minutes)		 Volume of gas (cm3)
Tablet X Tablet Y
0 0 0
1 38 32
2 48 54
3 48 67
4 48 72
5 48 72

i)
The graph shows the results for tablet X.

What is the volume of gas made by the end of the experiment?

Answer = ...................................... cm3 [1]

q18bi-paper-2-june-2018-ocr-gcse-chem

ii)
Plot the results for tablet Y on the grid. Draw a line of best fit.
[2]
iii)
Tablet X contains less calcium carbonate than tablet Y.

How do the results show this?
[1]

How did you do?

2c4 marks

The rate of reaction between calcium carbonate and hydrochloric acid can be increased by:

  • Using a more concentrated solution of hydrochloric acid
  • Increasing the temperature of the acid.

Explain how each of these methods increase the rate of the reaction.

Use ideas about collisions between particles.

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3a4 marks

A student investigates the rate of reaction between dilute hydrochloric acid and magnesium carbonate.

She wants to find out how the concentration of the acid changes the rate of reaction.

Fig. 18.1 shows the apparatus she uses.

fig-18-1-paper-2-nov-2020-ocr-gcse-chem

Carbon dioxide gas is given off in the reaction.

The student measures the loss in mass every 30 seconds for 5 minutes.

Another student also investigates the rate of reaction between dilute hydrochloric acid and magnesium carbonate.

Fig. 18.2 shows diagrams of some of the apparatus he uses.

fig-18-2-paper-2-nov-2020-ocr-gcse-chem

The student also wants to find out how the concentration of the acid changes the rate of reaction.

Describe the method he follows using the apparatus in Fig. 18.2.

Include a labelled diagram of the set-up of the apparatus he uses.

How did you do?

3b7 marks

The students now investigate the reaction between sodium thiosulfate and dilute hydrochloric acid.

They want to find out how temperature changes the rate of reaction.

Fig. 18.3 is a diagram of their experiment.

Add dilute hydrochloric acid and start timing

fig-18-3-paper-2-nov-2020-ocr-gcse-chem

A yellow solid is made during the reaction.

The students time how long it takes for the cross to disappear. This is the reaction time.

Look at their results.

Temperature (°C) Reaction Time (s)
10 140
20 56
30 34
40 26
50 22

i)

Plot a graph of the results on the grid. Draw a line of best fit.

q18bi-paper-2-nov-2020-ocr-gcse-chem

[3]

ii)
What is the reaction time at 25 °C?
Reaction time = ....................................................... s [1]

iii)
What happens to the rate of reaction as the temperature increases?

[1]
iv)
Explain your answer to (b)(iii). Include ideas about collisions between particles in your answer.

[2]

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4a2 marks

A student investigates the reaction between magnesium and dilute hydrochloric acid, HCl.

The student adds magnesium ribbon to hydrochloric acid in a beaker, as shown in the diagram.

q21-paper-2-june-2019-ocr-gcse-chem

Magnesium chloride, MgCl2, and hydrogen gas are made.

Write the balanced symbol equation for this reaction.

How did you do?

4b6 marks

The student measures the time it takes for all the magnesium to react. This is the reaction time.

The student does five experiments.

This is the student’s prediction:

“The smaller the volume of acid and the smaller the mass of magnesium, the shorter the reaction time.”

Look at the student’s results.

Experiment Mass of magnesium
used (g)		 Volume of acid used
(cm3)		 Concentration
of acid
(mol/dm3)		 Reaction time
(s)
1 0.05 25 1.0 30
2 0.05 50 1.0 30
3 0.05 50 2.0 15
4 0.10 25 1.0 30
5 0.10 50 2.0 15

Describe and explain whether the student’s results support his prediction.

Include ideas about the reacting particle model in your answer.

How did you do?

4c3 marks

The student repeats experiment 1. This time he uses acid at a lower temperature.

Explain, using the reacting particle model, what happens to the rate of reaction and predict the reaction time for this reaction.

How did you do?

4d2 marks

During chemical reactions, reactants are used up and the rate of reaction decreases.

Explain, in terms of particles, why the rate of reaction decreases.

How did you do?

4e3 marks

The student repeats experiment 3. This time he uses acid at a higher temperature.


Explain, using the reacting particle model, what happens to the rate of reaction and predict the reaction time for this reaction.

How did you do?

4f
Sme Calculator3 marks
Another student investigates the reaction between marble chips and hydrochloric acid.

She times how long it takes for all the marble chips to react.

Look at her results.

Experiment Size of marble chips Reaction time (s) Mean rate of reaction
(g/s)
1 large 240 8.33 × 10-4
2 large 120  
3 large 100 2.00 × 10-3
4 small 50 4.00 × 10-3

Look at the student’s results for experiment 2.

Calculate the mean rate of reaction in experiment 2.

Give your answer to 3 significant figures and in standard form.

Mean rate of reaction = ................................................... g/s

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5a2 marks

A student investigates the reaction between marble chips, CaCO3, and hydrochloric acid.

Calcium chloride, CaCl2, carbon dioxide and water are made.

Write a balanced symbol equation for the reaction.

How did you do?

5b
Sme Calculator4 marks

The student does three experiments, A, B and C.

q18b-paper-4-june-2018-ocr-gcse-chem

In each experiment she uses a different size of marble chip. She uses the same mass of marble in each experiment. She also uses the same concentration of acid.

Look at the graph of her results.

q18b2-paper-4-june-2018-ocr-gcse-chem

i)

Look at the line for experiment B on the graph.

When is the rate of reaction greatest?

Choose your answer from the list.

0 – 30 seconds
30 – 60 seconds
60 – 90 seconds
90 – 120 seconds

Answer = ..................................... seconds

[1]

ii)
Look at the line for experiment C.

Calculate the rate of reaction during the first 45 seconds.
   
Give your answer to 2 significant figures.


Answer = ..................................... cm3 / s

[3]

How did you do?

5c4 marks

The rate of reaction between marble and hydrochloric acid can be decreased by:

• Using a more dilute solution of hydrochloric acid
• Cooling the acid.

Explain how each of these methods make the reaction slower.

Use ideas about collisions between particles.

How did you do?

5d2 marks

A catalyst can be used to increase the rate of a reaction.

Look at the energy profile diagram for a reaction without a catalyst.

q18d-paper-4-june-2018-ocr-gcse-chem

Complete the energy profile diagram to show

i)
The reaction profile for the reaction with a catalyst. 

[1]

ii)
Label the activation energy for the reaction with a catalyst. 
[1]

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6a1 mark

A student added 2.4 g of magnesium to hydrochloric acid. She observed that no magnesium was left when the reaction was complete.

The student transferred the solution to an evaporating basin. She heated the solution using a Bunsen burner and evaporated all the water.

a)
Explain how you can tell from the student’s observation that the hydrochloric acid was in excess.
[1]

How did you do?

6b1 mark
b)
Look at the equation for the reaction.

Mg + 2HCl rightwards arrowMgCl2 + H2

The student knows the reaction is complete when there is no magnesium left.

Use the equation to explain one other way the student could tell that the reaction was complete.
[1]

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7a5 marks

A student investigates the rate of reaction between dilute hydrochloric acid and magnesium carbonate.

She wants to find out how the concentration of the acid changes the rate of reaction.

Look at the apparatus she uses.

q19-paper-4-nov-2020-ocr-gcse-chem

Carbon dioxide gas is given off in the reaction.

The student measures the loss in mass every 30 seconds for 5 minutes.

a)
Another student also investigates the rate of reaction between dilute hydrochloric acid and magnesium carbonate.

He also wants to find out how the concentration of the acid changes the rate of reaction. He uses a different method.

Describe the method he uses.

Include a labelled diagram of the set‑up of the apparatus he uses.

[5]

How did you do?

7b8 marks
b)
The students now investigate the reaction between sodium thiosulfate and dilute hydrochloric acid.

They want to find out how temperature changes the rate of reaction.

Look at the diagram of their experiment.

Add dilute hydrochloric acid and start timing
q19b-paper-4-nov-2020-ocr-gcse-chem

A yellow solid is made during the reaction.

The students time how long it takes for the cross to disappear. This is the reaction time.

Look at their results.

Temperature (°C) Reaction time (s) Rate of reaction (s−1)
10 140 7 × 10−3
20 56 2 × 10−2
30 34 3 × 10−2
40 26 4 × 10−2
50 22 5 × 10−2

i)

Plot a graph of the results on the grid. Draw a line of best fit.

q19bi-paper-4-nov-2020-ocr-gcse-chem

[4]

ii)
What happens to the rate of reaction as the temperature increases?.

[1]

iii)

Explain your answer to (b)(ii).

Use ideas about collisions between particles in your answer.

[3]

How did you do?

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