IGCSE Chemistry 0620 Paper 61, May/June 2024

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0620/61 · May/June 2024

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A student carries out a titration to find the concentration of a sample of dilute hydrochloric acid. The student: ● adds $25.0 {cm}^{3}$ of aqueous potassium hydroxide to the apparatus labelled A in Fig. 1.1 ● adds a few drops of a suitable indicator to the apparatus labelled A ● uses a burette to add dilute hydrochloric acid to the aqueous potassium hydroxide and indicator mixture in the apparatus labelled A.

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

[2]

b(i)

The student adds the indicator after the volume of the $25.0 {cm}^{3}$ of aqueous potassium hydroxide has been measured. Explain why the student adds an indicator to the aqueous potassium hydroxide.

[1]

b(ii)

Name a suitable indicator.

[1]

Describe how the student can determine the volume of dilute hydrochloric acid used in this titration.

[2]

The student observes the colour changes that occur as they add dilute hydrochloric acid from the burette. State one other thing the student should do as they add the dilute hydrochloric acid to the aqueous potassium hydroxide.

[1]

A student investigates the temperature change when magnesium reacts with dilute sulfuric acid. The student does five experiments. Experiment 1 ● Use a $25 {cm}^{3}$ measuring cylinder to pour $20 {cm}^{3}$ of dilute sulfuric acid into a boiling tube. ● Use a thermometer to measure the initial temperature of the acid in the boiling tube. Record the initial temperature. ● Add a coiled $5 cm$ length of magnesium ribbon to the acid in the boiling tube. At the same time start a timer. ● Continually stir the contents of the boiling tube using the thermometer. ● After 45 seconds, measure the temperature of the mixture in the boiling tube. Record this temperature. ● Rinse the boiling tube with distilled water. Experiment 2 ● Use the $25 {cm}^{3}$ measuring cylinder to pour $20 {cm}^{3}$ of dilute sulfuric acid into the boiling tube. ● Use a $10 {cm}^{3}$ measuring cylinder to add $2.0 {cm}^{3}$ of distilled water to the acid in the boiling tube. ● Place a bung in the boiling tube and invert the tube to mix the acid and water. ● Use the thermometer to measure the initial temperature of the contents of the boiling tube. Record the initial temperature. ● Add a coiled $5 cm$ length of magnesium ribbon to the contents of the boiling tube. At the same time start a timer. ● Continually stir the contents of the boiling tube using the thermometer. ● After 45 seconds, measure the temperature of the mixture. Record this temperature. ● Rinse the boiling tube with distilled water. Experiment 3 ● Repeat Experiment 2, adding $4.0 {cm}^{3}$ of distilled water instead of $2.0 {cm}^{3}$ . Experiment 4 ● Repeat Experiment 2, adding $6.0 {cm}^{3}$ of distilled water instead of $2.0 {cm}^{3}$ . Experiment 5 ● Repeat Experiment 2, adding $10.0 {cm}^{3}$ of distilled water instead of $2.0 {cm}^{3}$ .

Use the information in the description of the experiments and the thermometer diagrams to complete Table 2.1.

[5]

b(i)

State which Experiment, 1, 2, 3, 4 or 5, had the smallest temperature change.

[1]

b(ii)

Explain why the temperature change was smallest in the experiment you have given in (b)(i).

[1]

Complete a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on Fig. 2.1. Draw a line of best fit.

[4]

Use your graph in Fig. 2.1 to deduce the temperature increase when Experiment 2 is repeated with $7.5 {cm}^{3}$ of distilled water instead of $2.0 {cm}^{3}$ . Show clearly on Fig. 2.1 how you worked out your answer.

[2]

The average rate of temperature increase in each experiment is calculated using the equation shown. $average rate of temperature increase = \frac{temperature increase}{45 seconds}$ Calculate the average rate of temperature increase in Experiment 1. Give units for the rate you have calculated. average rate of temperature increase = .............................. units = ..............................

[2]

f(i)

Explain why the results of the experiment are more accurate if the boiling tube is wrapped in cotton wool.

[2]

f(ii)

Explain why a $25.0 {cm}^{3}$ volumetric pipette cannot be used to accurately measure the volume of the distilled water added.

[1]

f(iii)

State one other way in which the apparatus can be changed to give more accurate results.

[1]

Sketch on Fig. 2.1 the graph you would expect if all of the experiments were repeated using a $2 cm$ length of magnesium ribbon instead of the $5 cm$ length. Label your line g.

[1]

A student tests two substances: solution E and solid F. Tests on solution E Solution E is aqueous chromium(III) bromide. Solution E is divided into two portions. Record the expected observations.

To the first portion of solution E, the student adds aqueous sodium hydroxide dropwise and then in excess. observations adding dropwise ................................................................................................... .................................................................................................................................................... observation in excess ................................................................................................................ ....................................................................................................................................................

[2]

To the second portion of solution E, the student adds about $1 {cm}^{3}$ of dilute nitric acid and a few drops of aqueous silver nitrate. observations .............................................................................................................................. ..............................................................................................................................................

[1]

The observations in test 1 show that solid F is hydrated. Describe a chemical test to show that the condensation at the top of the boiling tube contains water. test ............................................................................................................................................. result ..........................................................................................................................................

[2]

From the tests and observations in Table 3.1 it is not possible to identify the cation in solid F. Give another test that can be carried out to help identify the cation in solid F.

[1]

Identify the anion in solid F.

[1]

A mixture contains three compounds: ● liquid ethanol ● solid sodium chloride ● solid zinc carbonate. Table 4.1 gives some information about these three compounds. Table 4.1

$name of compound$	$solubility in water$	$solubility in ethanol$
$ethanol$	$soluble$
$sodium chloride$	$soluble$	$insoluble$
$zinc carbonate$	$insoluble$	$insoluble$

Describe how to obtain a pure sample of each of the three compounds, ethanol, sodium chloride and zinc carbonate, from the mixture. You are provided with common laboratory apparatus.

[6]

Mark scheme

0620/61 · May/June 2024

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1a · 2 marks

M1
A (conical) flask
M2
B volumetric pipette

1b(i) · 1 mark

1 mark
so that it can change colour at the end point

1b(ii) · 1 mark

1 mark
methyl orange / thymolphthalein

1c · 2 marks

M1
take initial and final (burette) readings
M2
final reading minus initial reading

1d · 1 mark

1 mark
swirl (A) / swirl (the flask) / mix (the contents of A)

2a · 5 marks

M1
all five volumes of dilute sulfuric acid are 20
M2
all five volumes of water are correct (0, 2, 4, 6, 10)
M3
all temperatures and temperature changes are recorded to nearest 0.5 °C
M4
all five temperatures after 45 seconds are recorded correctly (37.0, 34.0, 31.5, 30.0, 27.5)
M5
all temperature increases correct (12.0, 8.5, 6.0, 4.0, 1.5)

2b(i) · 1 mark

1 mark
5

2b(ii) · 1 mark

1 mark
larger / largest volume (being heated)

2c · 4 marks

M1
suitable sensible scale on y-axis
M2
all five points plotted correctly
M3
all five points plotted correctly
M4
best fit line

2d · 2 marks

M1
correct working shown on graph
M2
correct value from their working to a point on the line

2e · 2 marks

M1
(12 ÷ 45 =) 0.27 or 0.267 or 0.3
M2
°C / s

2f(i) · 2 marks

1 mark
insulator
1 mark
so reduces / prevents heat loss / traps heat / temperature (more) accurate / does not cool down / prevents temperature decreasing

2f(ii) · 1 mark

1 mark
volume used is not fixed / volume needed is not the same in each experiment / volume used is not 25 cm3

2f(iii) · 1 mark

1 mark
use a burette instead of a measuring cylinder

2g · 1 mark

1 mark
sketch line is below results line for all volumes of water

3a · 2 marks

M1
green precipitate
M2
precipitate dissolves (giving a green solution) / soluble (in excess) / precipitate disappears

3b · 1 mark

1 mark
cream precipitate

3c · 2 marks

M1
anhydrous copper(II) sulfate / anhydrous cobalt(II) chloride
M2
(changes from white to) blue / (changes from blue to) pink

3d · 1 mark

1 mark
flame test

3e · 1 mark

1 mark
sulfate / SO42–

4 · 6 marks

1 mark
filter the initial mixture (ethanol obtained as filtrate)
1 mark
add water to the residue / mixture
1 mark
stir / warm after adding water
1 mark
filter after adding water
1 mark
wash residue from filtration after the addition of water
1 mark
dry the solid zinc carbonate / heat filtrate to remove water and obtain solid sodium chloride

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