IGCSE Chemistry 0620 Paper 63, May/June 2025

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0620/63 · May/June 2025

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Fermentation is a process in which yeast is used to convert aqueous glucose to ethanol and carbon dioxide. Fermentation takes place at a temperature of between 25C and 35C. $C_{6} H_{12} O_{6} (a q) \to 2 C_{2} H_{5} O H (a q) + 2 C O_{2} (g)$ A student uses the apparatus shown in Fig. 1.1 to make carbon dioxide by fermentation.

Name the items of apparatus labelled A and B in Fig. 1.1. A ............................................................................................................................................... B ...............................................................................................................................................

[2]

Suggest why a water-bath is used.

[1]

The student measures the volume of gas that is collected every 10 minutes for 90 minutes. Their results are shown in Fig. 1.2. Describe how the results in Fig. 1.2 show that the fermentation is not complete after 90 minutes.

[1]

d(i)

The student repeats the experiment using the apparatus shown in Fig. 1.3. State what happens to the appearance of the limewater during fermentation.

[1]

d(ii)

State one observation the student would make that shows that fermentation is complete.

[1]

State the method the student should use to obtain ethanol from the fermentation mixture.

[1]

A student investigates how the rate of reaction between dilute hydrochloric acid and aqueous sodium thiosulfate changes as the concentration of the aqueous sodium thiosulfate decreases. During the reaction, the solution slowly becomes cloudy. As the solution becomes cloudy, it becomes more difficult to see through the solution. The student does five experiments. Experiment 1 • Use a $50 c m^{3}$ measuring cylinder to pour $50 c m^{3}$ of aqueous sodium thiosulfate into a $100 c m^{3}$ beaker. • Use a $10 c m^{3}$ measuring cylinder to pour $5 c m^{3}$ of dilute hydrochloric acid into the beaker containing the aqueous sodium thiosulfate. • Immediately start a stop-watch and stir the contents of the beaker. • Stand the beaker on a printed sheet and look down from above the beaker as shown in Fig. 2.1. • When the text on the printed sheet is not visible, stop the stop-watch and record the time to the nearest whole number of seconds. • Empty the contents of the beaker and rinse the beaker with distilled water. Experiment 2 • Repeat Experiment 1 using $40 c m^{3}$ of aqueous sodium thiosulfate instead of $50 c m^{3}$ . Use the $50 c m^{3}$ measuring cylinder to add $10 c m^{3}$ of distilled water to the beaker before adding the dilute hydrochloric acid. Experiment 3 • Repeat Experiment 2 using $30 c m^{3}$ of aqueous sodium thiosulfate and $20 c m^{3}$ of distilled water. Experiment 4 • Repeat Experiment 2 using $25 c m^{3}$ of aqueous sodium thiosulfate and $25 c m^{3}$ of distilled water. Experiment 5 • Repeat Experiment 2 using $20 c m^{3}$ of aqueous sodium thiosulfate and $30 c m^{3}$ of distilled water.

Use the information in the description of the experiments and the stop-watch diagrams to complete Table 2.1.

[3]

Write a suitable scale on the y-axis and plot the results from Experiments 1 to 5 on Fig. 2.2. Draw a curve of best fit.

[4]

c(i)

The relative rate of reaction in each experiment is calculated using the equation shown. $relative rate of reaction = \frac{1}{time taken}$ Calculate the relative rate of reaction in Experiment 1. Do not give units for your answer. relative rate of reaction = ..............................

[1]

c(ii)

State in which Experiment, 1, 2, 3, 4 or 5, the relative rate of reaction was greatest.

[1]

d(i)

In each experiment the total volume of aqueous sodium thiosulfate and distilled water is constant. Calculate the volume of distilled water needed when the volume of aqueous sodium thiosulfate is $37 c m^{3}$ . volume = ..............................

[2]

d(ii)

From your graph in Fig. 2.2, deduce the time for the text to not be visible when the volume of aqueous sodium thiosulfate is $37 c m^{3}$ . Show clearly on Fig. 2.2 how you worked out your answer. time = .............................. s

[2]

d(iii)

Explain why the total volume of aqueous sodium thiosulfate and distilled water is kept constant.

[1]

e(i)

State why measuring the volume of the dilute hydrochloric acid with a burette instead of a measuring cylinder would be an improvement.

[1]

e(ii)

Explain why it is not possible to use a volumetric pipette to measure the volume of aqueous sodium thiosulfate in each experiment.

[1]

Explain why it is important not to change the size of the beaker to a larger beaker during the investigation.

[2]

A student tests two solids: solid L and solid M.

Tests on solid L Solid L is hydrated aluminium chloride. The student dissolves solid L in distilled water to form solution L. Solution L is divided into four approximately equal portions. To the first portion of solution L, the student adds aqueous sodium hydroxide dropwise and then in excess. observations when added dropwise ......................................................................................... observations in excess .............................................................................................

[2]

To the second portion of solution L, the student adds aqueous ammonia dropwise and then in excess. observations when added dropwise ......................................................................................... observations in excess .............................................................................................

[2]

To the third portion of solution L, the student adds about $1 c m^{3}$ of dilute nitric acid followed by a few drops of aqueous silver nitrate. observations ............................................................................................................................. .............................................................................................................................................

[1]

To the fourth portion of solution L, the student adds about $1 c m^{3}$ of dilute nitric acid followed by a few drops of aqueous barium nitrate. observations ............................................................................................................................. .............................................................................................................................................

[1]

Tests on solid M Table 3.1 shows the tests and the student’s observations for solid M. Identify the gas given off in test 3.

[1]

Identify solid M.

[2]

Lead(II) chloride, $P b C l_{2}$ , is an insoluble salt. Solid lead(II) chloride can be made by reacting aqueous sodium chloride with aqueous lead(II) nitrate. $2 N a C l (a q) + P b (N O_{3})_{2} (a q) \to 2 N a N O_{3} (a q) + P b C l_{2} (s)$ Describe how to make a pure, dry sample of solid lead(II) chloride. You are provided with solid sodium chloride, solid lead(II) nitrate, distilled water and common laboratory apparatus.

[6]

Mark scheme

0620/63 · May/June 2025

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1a · 2 marks

1 mark
A (conical) flask
1 mark
B (gas) syringe

1b · 1 mark

1 mark
to keep (the contents of the flask) warm / at 25 °C to 35 °C

1c · 1 mark

1 mark
gas volume still increasing / gas volume not constant

1d(i) · 1 mark

1 mark
(turns) milky / cloudy

1d(ii) · 1 mark

1 mark
no more bubbles

1e · 1 mark

1 mark
(fractional) distillation

2a · 3 marks

M1
volume of aqueous sodium thiosulfate and volume of water correctly recorded for all five experiments and volume of dilute hydrochloric acid shown as 5 cm3 for all experiments: (50, 0, 5), (40, 10, 5), (30, 20, 5), (25, 25, 5), (20, 30, 5)
M2
all five stop clock reading correct: 30, 37, 49, 59, 73
M3
all times in whole number of seconds only

2b · 4 marks

M1
y-axis linear scale linear and points extend over more than half of the y-axis
M2
points plotted correctly (first mark)
M3
all points plotted correctly (second mark)
M4
line of best fit

2c(i) · 1 mark

1 mark
correct evaluation of 1 ÷ time for experiment one. expected answer is 1 / 30 = 0.033

2c(ii) · 1 mark

1 mark
1

2d(i) · 2 marks

M1
13
M2
cm3

2d(ii) · 2 marks

M1
correct working shown at 37 cm3 on graph to show where value read
M2
correct reading from their working shown on graph.

2d(iii) · 1 mark

1 mark
so depth of liquid in beaker is the same in all experiments / so concentration of dilute hydrochloric acid in mixture is the same for all experiments

2e(i) · 1 mark

1 mark
a burette is more accurate than a measuring cylinder

2e(ii) · 1 mark

1 mark
volume of aqueous sodium thiosulfate is not 25 cm3
1 mark
volume of aqueous sodium thiosulfate is not constant / fixed
1 mark
volumetric pipettes not available in those sizes

2f · 2 marks

M1
(different size beaker would) change depth
M2
so changes time measured

3a · 2 marks

M1
dropwise: white precipitate
M2
excess: precipitate dissolves

3b · 2 marks

M1
dropwise: white precipitate
M2
excess: precipitate remains / no change

3c · 1 mark

1 mark
white precipitate

3d · 1 mark

1 mark
no change

3e · 1 mark

1 mark
ammonia / NH3

3f · 2 marks

M1
barium / Ba2+
M2
nitrate / NO3–

4 · 6 marks

1 mark
add sodium chloride / lead nitrate to water
1 mark
stir / mix / shake (to dissolve)
1 mark
add / combine / mix the two reactants together
1 mark
use of a suitable container
1 mark
filter (to obtain lead(II) chloride as residue)
1 mark
pour water over the residue (in the funnel)
1 mark
description of how to dry the solid

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