IGCSE Chemistry 0620 Paper 63, Oct/Nov 2024

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0620/63 · Oct/Nov 2024

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When crystals of hydrated calcium ethanedioate, ${C a C}_{2} O_{4} \cdot H_{2} O$ , are heated they decompose to form solid calcium carbonate, steam and carbon monoxide gas. ${C a C}_{2} O_{4} \cdot H_{2} O (s) \to {C a C O}_{3} (s) + H_{2} O (g) + C O (g)$ A student suggests using the apparatus shown in Fig. 1.1 to decompose hydrated calcium ethanedioate and obtain the products. Table 1.1 shows some information about carbon monoxide. Table 1.1

	$melting point /^{\circ} C$	$boiling point /^{\circ} C$	$density compared to air$	$solubility in water$	$safety warning$
$carbon monoxide$	-205	-192	$about the same$	$insoluble$	$toxic$

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

[2]

The apparatus shown in Fig. 1.1 will not work because there is an error in how the gas is collected. This error makes it dangerous to use the apparatus. Identify the error and explain why this error makes it dangerous to use the apparatus. error ........................................................................................................................................... .................................................................................................................................................... explanation ................................................................................................................................ ....................................................................................................................................................

[2]

Complete Fig. 1.2 to show how the gas could be collected safely.

[1]

Add one arrow to Fig. 1.2 to show where the apparatus should be heated.

[1]

Identify the substance that collects at the point marked X on Fig. 1.2.

[1]

Suggest why this experiment should be carried out in a fume cupboard.

[1]

A student investigates the temperature change when solid P dissolves in water. The student does two experiments. Experiment 1 ● Use a $25 {c m}^{3}$ measuring cylinder to pour $20 {c m}^{3}$ of distilled water into a boiling tube. ● Use a thermometer to measure the temperature of the distilled water. This is the temperature at $time = 0 seconds$ . ● Add a $5 g$ sample of solid P to the distilled water in the boiling tube. At the same time start a stop-watch. ● Continually stir the contents of the boiling tube using the thermometer. ● Measure the temperature of the mixture in the boiling tube every 20 seconds for 120 seconds. ● Rinse the boiling tube with distilled water. Experiment 2 ● Repeat Experiment 1 using $10 {c m}^{3}$ of distilled water instead of the $20 {c m}^{3}$ of distilled water.

Complete Table 2.1 by using the thermometer diagrams and calculating the temperature decreases from the temperature at 0 seconds. For example, at 60 seconds: $temperature decrease = temperature at 0 s - temperature at 60 s$ Table 2.1

[5]

Complete a suitable scale on the y-axis and plot the results from Experiment 1 and Experiment 2 on Fig. 2.1. Draw two lines of best fit. Both of your lines of best fit must go to (0,0). Label both lines.

[4]

State whether the energy change in Experiment 1 is exothermic or endothermic. Explain your answer.

[1]

Compare the maximum temperature decrease in Experiment 1 with the maximum temperature decrease in Experiment 2.

[2]

From your graph in Fig. 2.1, deduce the temperature decrease in Experiment 2 after 45 seconds. Show clearly on Fig. 2.1 how you worked out your answer. temperature decrease = .............................. °C

[2]

The average rate of temperature decrease in each experiment can be calculated using the equation shown. $average rate of temperature decrease = \frac{temperature decrease}{time}$ Calculate the average rate of temperature decrease in Experiment 1 for 120 seconds. Give units for the average rate you have calculated. average rate of temperature decrease = .............................. units = ..............................

[2]

State two possible sources of error in these experiments. For each source of error, suggest an improvement which reduces the error. source of error 1 ........................................................................................................................ improvement 1 ........................................................................................................................... .................................................................................................................................................... source of error 2 ........................................................................................................................ improvement 2 ........................................................................................................................... ....................................................................................................................................................

[4]

A student tests two substances: solid R and solid S. Tests on solid R Table 3.1 shows the tests and the student's observations for solid R. Table 3.1

tests	observations
test 1
$Gently heat about half of solid R in a boiling tube.$	$the white solid forms a colourless liquid$
	$steam comes out from the boiling tube and condensation forms at the top of the boiling tube$
test 2
$The remaining solid R is dissolved in distilled water to form solution R. Solution R is divided into four portions.$	$white precipitate forms$
$To the first portion of solution R, add aqueous sodium hydroxide dropwise and then in excess.$	$the white precipitate dissolves in excess aqueous sodium hydroxide$
test 3
$To the second portion of solution R, add aqueous ammonia dropwise and then in excess.$	$white precipitate forms$
	$the white precipitate remains in excess aqueous ammonia$
test 4
$To the third portion of solution R, add$ $1 {c m}^{3}$ $of dilute nitric acid followed by a few drops of aqueous barium nitrate.$	$no change$
test 5
$To the fourth portion of solution R, add$ $1 {c m}^{3}$ $of dilute nitric acid followed by a few drops of aqueous silver nitrate.$	$cream precipitate forms$

State the conclusion that can be made from the observations in test 1.

[1]

Identify solid R.

[2]

Tests on solid S Solid S is sodium sulfite. Record the expected observations. The student carries out a flame test on solid S. observations ........................................................................................................................

[1]

The student dissolves the remaining solid S in distilled water to form solution S. The student divides solution S into two portions. To the first portion of solution S, the student adds about $2 {c m}^{3}$ of aqueous sodium hydroxide. observations ........................................................................................................................

[1]

To the second portion of solution S, the student adds a few drops of acidified aqueous potassium manganate(VII). observations ........................................................................................................................

[1]

A mixture contains three solid compounds: ● aluminium oxide ● calcium carbonate ● calcium chloride. Table 4.1 gives some information about the three compounds in the mixture. Table 4.1

$name of compound$	$solubility in water$	$effect of adding aqueous sodium hydroxide$
$aluminium oxide$	$insoluble$	$reacts to form a soluble compound$
$calcium carbonate$	$insoluble$	$no effect$
$calcium chloride$	$soluble$	$reacts to form an insoluble compound$

Plan an experiment to find the percentage by mass of calcium carbonate in the mixture. Your plan must include how you will calculate the percentage by mass of calcium carbonate in the mixture. You are provided with a sample of the mixture, distilled water, aqueous sodium hydroxide and common laboratory apparatus.

[6]

Mark scheme

0620/63 · Oct/Nov 2024

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1a · 2 marks

M1
A beaker
M2
B delivery tube

1b · 2 marks

M1
error: using a bung (in collecting tube) / the apparatus is sealed
M2
explanation: (pressure would increase and so the apparatus / tube would) explode/break

1c · 1 mark

1 mark
diagram showing collection over water OR using a gas syringe

1d · 1 mark

1 mark
an arrow pointing to the hydrated calcium ethanedioate

1e · 1 mark

1 mark
water / H2O

1f · 1 mark

1 mark
carbon monoxide is toxic

2a · 5 marks

M1
all six temperatures for Experiment 1 correct (22.5, 21.0, 20.0, 19.5, 19.0, 19.0)
M2
all six temperature decreases for experiment 1 correct (1.5, 3.0, 4.0, 4.5, 5.0, 5.0)
M3
all six temperatures for Experiment 2 correct (19.5, 17.0, 15.5, 14.0, 13.5, 13.0)
M4
all six temperature decreases for Experiment 2 correct (3.5, 6.0, 7.5, 9.0, 9.5, 10.0)
M5
all temperatures and temperature changes are recorded to 1dp

2b · 4 marks

M1
suitable scale on y-axis
M2
all points plotted correctly (first mark)
M3
all points plotted correctly (second mark)
M4
best-fit curves AND at least one line labelled

2c · 1 mark

1 mark
endothermic AND temperature decreases

2d · 2 marks

M1
maximum temperature change / decrease is greater in Experiment 2
M2
quantitative answer (e.g. 2 times greater in Experiment 2)

2e · 2 marks

M1
correct construction at 45 s shown on Fig 2.1
M2
correct reading

2f · 2 marks

M1
correct evaluation of temperature change in Experiment 1 ÷ 120 (5 / 120 = 0.0417)
M2
°C/s

2g · 4 marks

1 mark
error: heat gain / (volume of water due to using a) measuring cylinder / water already in boiling tube for Experiment 2
1 mark
improvement: insulate / (use a) lid / (use a) polystyrene (cup) / (use a) burette / dry / clean / new boiling tube
1 mark
error: second valid error identified
1 mark
improvement: second corresponding improvement

3a · 1 mark

1 mark
(R is) hydrated / has water of crystallisation

3b · 2 marks

M1
aluminium / Al3+
M2
bromide / Br–

3c · 1 mark

1 mark
yellow (flame)

3d · 1 mark

1 mark
no change / no reaction / remains colourless

3e · 1 mark

1 mark
becomes colourless / (pink / purple) is decolourised

4 · 6 marks

M1
MP1 find mass of mixture
M2
MP2 add water and stir
M3
MP3 filter
M4
MP4 add (excess) aqueous sodium hydroxide to residue and stir
M5
MP5 filter and wash residue / calcium carbonate (with water) and dry
M6
MP6 weigh residue / calcium carbonate

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