Rates of Reaction (Edexcel GCSE Chemistry: Combined Science)

Exam Questions

3 hours21 questions

1a1 mark

A student used the equipment in Figure 6 to investigate the rate of reaction between zinc and excess dilute hydrochloric acid.

fig-5-q6-1cho-2f-specimen-2018

Figure 6

The student uses the following method:

place a known mass of granulated zinc into the conical flask
pour 25 cm³of dilute hydrochloric acid (an excess) into the conical flask and fit the bung quickly into the neck of the flask
measure the volume of gas produced every 20 seconds until after the reaction finishes.

Figure 7 shows the results.

time / s	volume of hydrogen / cm³
0	0
20	42
40	66
60	75
80	80
100	82
120	82
140	82

Figure 7

Give the name of a piece of equipment that can be used to measure 25 cm³of dilute hydrochloric acid accurately.

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1b3 marks

Draw a graph of the volume of hydrogen gas produced against time using the grid.

fig-q5b-1cho-2f-specimen-2018

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1 mark

The average rate of reaction in the first 20 seconds in cm³of hydrogen produced per second is

☐	A	2.1
☐	B	8.4
☐	C	21
☐	D	84

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1d2 marks

The student repeated the experiment keeping all conditions the same but using the same mass of powdered zinc instead of granulated zinc.

On the grid above sketch the graph you would expect when the experiment is repeated using powdered zinc.
Label your line A.

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1e3 marks

Sodium thiosulfate solution, Na₂S₂O₃, reacts with dilute hydrochloric acid as shown in the equation.

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

The rate of this reaction can be investigated by mixing the reactants and finding the time taken for a precipitate of sulfur to become visible.

A student wants to investigate the effect of changing the temperature on the rate of this reaction.

Devise a method the student could use to find out how the time taken for the precipitate of sulfur to become visible changes with temperature.

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5a1 mark

Hydrogen peroxide decomposes to form water and oxygen.

The rate of this reaction can be found by measuring the volume of oxygen formed after different time intervals.

Hydrogen peroxide solution is placed in a conical flask.
The apparatus is set up as shown in Figure 5.

fig-5-q3-1cho-2f-paper-1-june-2018

Figure 5

State the name of the piece of apparatus labelled Z in Figure 5.

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5b1 mark

At the end of the reaction the bung is removed from the conical flask.
A glowing splint is put into the gas in the flask.

State what you would see.

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5c3 marks

A solid catalyst can be used for this reaction.

The experiment is repeated under identical conditions but with the catalyst added.

In the experiment with the catalyst added

(1)

☐	A	the rate of reaction is the same as when no catalyst is present
☐	B	water and oxygen are the only products of the reaction
☐	C	some of the catalyst is used up
☐	D	the volume of oxygen produced when all the hydrogen peroxide is decomposed is larger than when no catalyst is present

ii)

At the end of the experiment with the catalyst added, the mass of the catalyst remaining is found.

The method used to find the mass of the catalyst remaining is

filter the mixture of products and catalyst
determine the mass of the filter paper and solid catalyst
subtract the mass of a filter paper from the mass of filter paper and solid catalyst.

This method would not give the accurate mass of catalyst remaining.

Which of the following needs to be done to give a more accurate mass?

(1)

☐	A	dry the filter paper and catalyst before finding their mass
☐	B	scrape the catalyst off the filter paper and find the mass of the catalyst
☐	C	find the mass of the filtrate and not the filter paper and catalyst
☐	D	repeat the experiment

iii)

A given mass of catalyst is more effective if it has a large surface area.

State how you could increase the surface area of some lumps of solid catalyst.

(1)

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5d2 marks

The experiment is repeated three times

once using a more dilute solution of hydrogen peroxide
once using a lower temperature
once using a larger flask

In each case, all other conditions are kept the same.

Circle the word that shows the change in the rate of decomposition in each case.

	change in rate
hydrogen peroxide solution is more dilute	faster slower unchanged
the temperature used is lower	faster slower unchanged
the reaction is carried out in a larger flask	faster slower unchanged

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5e2 marks

Complete the balanced equation for the reaction and fill in the two missing state symbols.

.......... H₂O₂(aq) $\to$ 2H₂O (..........) + O₂(..........)

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4 marks

The rate of reaction between magnesium ribbon and dilute hydrochloric acid at room temperature is investigated.

The apparatus used is shown in Figure 1.

The volume of hydrogen gas given off was measured at regular intervals during the reaction.

fig-11-q9a-1cho-2h-paper-1-june-2018

Figure 1

The graph in Figure 2 shows the results of this experiment.

fig-12-q9a-1cho-2h-paper-1-june-2018

Figure 2

State a change that can be made to the apparatus in Figure 1 to measure the volumes of gas more accurately.

(1)

ii)

A tangent has been drawn to the line on the graph in Figure 2.

Calculate the rate of reaction at this point.

(2)

rate of reaction = .............................................. cm³s^-1

iii)

On the graph in Figure 2, draw the line you would expect to obtain if the magnesium ribbon in this experiment was replaced with an equal mass of powdered magnesium. All other conditions are kept the same.

(1)

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2 marks

Higher Only

The balanced equation for this reaction is

Mg + 2HCl $\to$ MgCl₂ + H₂

In another experiment, 0.1 moles of hydrochloric acid, HCl, were reacted with 0.1 g of magnesium ribbon.

Calculate the number of moles of magnesium, Mg, in the 0.1 g sample of magnesium ribbon.

(relative atomic mass: Mg = 24)

(1)

number of moles = .........................................

ii)

In a further experiment, 0.5 mol of hydrochloric acid, HCl, were mixed with 0.5 mol of magnesium, Mg.

Use the equation to show that, in this experiment, the magnesium is in excess.

(1)

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1c6 marks

Two substances, A and B, each form a colourless solution.

If the solutions are mixed in a beaker, A and B react to form a coloured product.

The rate of the reaction between A and B can be investigated by placing the beaker containing the mixture on a cross on a piece of paper and timing how long it takes for enough coloured product to be produced to make the cross invisible when viewed from above, through the solution.

	experiment 1	experiment 2	experiment 3
concentration of A in solution in g dm^-3	10	10	40
temperature in °C	20	40	40
time for cross to become invisible in s	320	80	20

Figure 3

Use the results of these experiments to explain, in terms of the behaviour of particles, the effect of changing temperature and the effect of changing the concentration of A in solution on the rate of this reaction.

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4a2 marks

A student uses this apparatus to investigate the rate of reaction between magnesium and an excess of dilute hydrochloric acid. The apparatus is shown in Figure 1.

mg-and-hcl-gas-syringe-experiment

Figure 1

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 in Figure 2.

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

Figure 2

Plot the student's results on the grid.

(1)

ii)

Draw a curve of best fit in Figure 3.

(1)

Figure 3

How did you do?

4b4 marks

The student repeats the experiment using

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

On Figure 3 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

On Figure 3 draw, on the grid in part (a), the curve you would expect in this experiment.

Label this curve Z.

(2)

How did you do?

4c1 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.

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4d2 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.

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4e3 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.

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		Feature 1	Feature 2
☐	A	Lower activation energy for the reaction	More products made in total
☐	B	Alternative pathway for the reaction is provided	Not used up over the course of the reaction
☐	C	Makes industrial processes cheaper	Metal catalysts are cheap to buy
☐	D	Reduce the overall energy change of the reaction	Can be present in biological systems as enzymes

concentration of hydrochloric acid in mol dm^–3	volume of gas collected in cm³
concentration of hydrochloric acid in mol dm^–3	small lumps of calcium carbonate	large lumps of calcium carbonate
0.50	17.2	3.1
1.0	35.1	5.6

size of calcium carbonate pieces used	volume of carbon dioxide gas produced in five minutes in cm³
large	16
small	48
powder	90

step 1	pour 25 cm³of dilute sulfuric acid into a conical flask
step 2	warm the acid until its temperature is 30 °C
step 3	add a piece of magnesium to the acid
step 4	start a stopwatch
step 5	wait until the reaction has finished
step 6	stop the stopwatch
step 7	repeat steps 1–6 but at 50 °C.

Catalyst	Time for mixture to become colourless in s
no catalyst	57
cobalt(II) chloride solution	34
copper(II) sulfate solution	10
iron(II) sulfate solution	29
zinc nitrate solution	77

condition	experiment 1	experiment 2
temperature / °C	30	20
pressure / atm	1	2

☐	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

☐	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	2.9 mol s^-1
☐	B	2.0 mol s^-1
☐	C	0.05 mol s^-1
☐	D	0.005 mol s^-1

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

☐	A	CaCO₂
☐	B	CaCO₃
☐	C	Ca(CO)₃
☐	D	Ca(CO₃)₂