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Thermal decomposition

Edexcel IGCSE Chemistry

Topic questions Chemical changes Thermal decomposition

Thermal decomposition

10 questions · 106 marks · about 2 hours

Thermal decomposition questions

TopicThermal decomposition

Chemistry Paper 1 November 2023, Question 4 11 marks

This question is about gases.

(a)

The table gives information about five gases.

Name of gas	argon	carbon dioxide	hydrogen	oxygen	nitrogen
Formula of gas	Ar	CO₂	H₂	O₂	N₂
M_r of gas	40		2	32	28

Use information from the table to answer these questions. Each gas may be used once, more than once or not at all.

(a)(i)

Give the name of the gas that is about 79 % of the atmosphere by volume.

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(a)(ii)

Give the name of the gas that is a compound.

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(a)(iii)

Give the name of the least reactive gas.

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(a)(iv)

Give the name of the gas that is not normally found in the atmosphere.

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(a)(v)

Give the name of the gas that affects global warming.

[1]

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(a)(vi)

Calculate the M_r for carbon dioxide.

[1]

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(a)(vii)

Give a reason why it is not possible to give information for air in the table.

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(b)

When copper(II) carbonate is heated, the products are copper(II) oxide and carbon dioxide.

(b)(i)

Give the name for this type of reaction.

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(b)(ii)

Give the colour change that occurs during this reaction.

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(b)(iii)

Give a chemical equation for this reaction.

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Chemistry Paper 2 June 2023, Question 2 10 marks

This question is about gases in the atmosphere.

(a)

Which of these gases has the lowest percentage by volume in the atmosphere?

$Question 2, shown as an image$

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(b)

When copper(II) carbonate is heated, copper(II) oxide and carbon dioxide form.

(b)(i)

What is the name of this type of reaction?

$Question 2, shown as an image$

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(b)(ii)

Which colour change occurs when copper(II) carbonate is heated?

$Question 2, shown as an image$

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(b)(iii)

Give the chemical equation for this reaction.

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(c)

A student uses this apparatus to find the percentage of oxygen in a sample of air.

The student leaves the apparatus until there is no further change in volume of gas in the syringe.

These are the student’s results.

Calculate the percentage of oxygen in the sample of air.

Give your answer to two significant figures.

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(d)

Explain why an increasing amount of carbon dioxide in the atmosphere is likely to cause a problem for the environment.

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Chemistry Paper 1 January 2023 (R), Question 8 12 marks

This question is about the oxides of some elements in Group 4 of the Periodic Table.

(a)

When 5.34 g of lead(II) carbonate are heated, lead(II) oxide and carbon dioxide are formed.

This is the equation for the reaction.

$Question 8, shown as an image$

(a)(i)

Give the name for this type of reaction.

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(a)(ii)

Calculate the maximum mass of lead(II) oxide that can be formed from 5.34 g of lead(II) carbonate.

[for PbCO₃, M_r = 267 for PbO, M_r = 223]

[2]

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(b)

The diagram shows apparatus used to heat lead(II) carbonate.

(b)(i)

Complete the diagram to show what needs to be added to the apparatus to test that the gas released is carbon dioxide.

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(b)(ii)

Give the result of the test.

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(c)

Silicon dioxide (SiO₂) and carbon dioxide both contain covalent bonds.

Silicon dioxide is a solid with a high melting point. Carbon dioxide is a gas at room temperature.

Explain why silicon dioxide has a much higher melting point than carbon dioxide.

Refer to structure and bonding in your answer.

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Chemistry Paper 1 June 2022 (R), Question 5 11 marks

This question is about metal carbonates.

When heated, some metal carbonates decompose to form a metal oxide and carbon dioxide gas.

(a)

A student is given three solid metal carbonates, a timer, some limewater and this apparatus.

Describe a method the student can use to find out which metal carbonate decomposes fastest when heated.

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(b)

A student is given a solid metal carbonate with the formula XCO₃

X represents the symbol of a Group 2 metal.

A student uses this apparatus to heat a sample of XCO₃ until it all decomposes.

The equation for the decomposition of XCO₃ is

$Question 5, shown as an image$

The student records the mass of XCO₃ and the mass of carbon dioxide that escapes through the cotton wool plug.

These are the student’s results.

$Question 5, shown as an image$

(b)(i)

Give a reason why the student uses a cotton wool plug.

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(b)(ii)

Calculate the amount, in mol, of carbon dioxide produced.

[for carbon dioxide M_r = 44]

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(b)(iii)

Use the equation to determine the amount, in mol, of XCO₃ that decomposed.

$Question 5, shown as an image$

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(b)(iv)

Use the mass of XCO₃ and your answer to (b)(iii) to calculate the relative formula mass (M_r) of XCO₃

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(b)(v)

Use your answer to (b)(iv) and the Periodic Table on page 2 to determine the identity of the Group 2 metal X.

Show your working.

[2]

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Chemistry Paper 1 June 2022, Question 7 13 marks

This question is about copper and copper compounds.

(a)

A sample of copper contains two isotopes.

• Cu-63 with relative abundance 69.5%

• Cu-65 with relative abundance 30.5%

(a)(i)

State what is meant by the term isotopes.

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(a)(ii)

Calculate the relative atomic mass (A_r) of this sample of copper.

Give your answer to three significant figures.

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(b)

When copper(II) carbonate is heated, copper(II) oxide and carbon dioxide are formed.

(b)(i)

What is the name of this type of reaction?

$Question 7, shown as an image$

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(b)(ii)

Which colour change occurs during this reaction?

$Question 7, shown as an image$

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(c)

A student uses this apparatus to find the value of x in the formula CuSO₄.xH₂O

This is the student’s method.

• find the mass of an empty boiling tube

• add hydrated copper(II) sulfate to the tube and record the new mass

• heat the hydrated copper(II) sulfate until it changes colour

• allow the tube to cool and record the mass again

The table shows the student’s results.

(c)(i)

Calculate the mass of CuSO₄ formed.

$Question 7, shown as an image$

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(c)(ii)

Calculate the mass of water formed.

[1]

(c)(iii)

Show that the value of x is approximately 4

[M_r of CuSO₄ = 159.5 M_r of H₂O = 18]

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(c)(iv)

The actual value of x is 5

Give a reason why the calculated value of x is lower than the actual value.

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Chemistry Paper 2 January 2022, Question 2 8 marks

This question is about gases in the air.

The pie chart represents the percentages of gases in dry, unpolluted air.

Gases with percentages of less than 1% in air are called trace gases.

(a)(i)

Which of these is gas Z?

$Question 2, shown as an image$

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(a)(ii)

Which of these is the approximate percentage of oxygen in dry, unpolluted air?

$Question 2, shown as an image$

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(b)

One of the trace gases is carbon dioxide.

(b)(i)

Identify two reactions that produce carbon dioxide by placing a tick (✓) in two boxes.

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(b)(ii)

Name an environmental problem that is caused by the percentage of carbon dioxide increasing in the atmosphere.

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(b)(iii)

Name the trace gas with the highest percentage in dry, unpolluted air.

[1]

(c)

Rainwater is acidic because carbon dioxide dissolves in water to form carbonic acid.

Acid rain is more acidic than rainwater because acidic pollutant gases also dissolve in water.

(c)(i)

Give the name of the acid that forms when nitrogen dioxide dissolves in water.

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(c)(ii)

Name another pollutant gas that also forms acid rain.

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Chemistry Paper 1 January 2021 (R), Question 5 12 marks

Also involves Factors affecting the rate of reaction

A student uses this apparatus to investigate the effect of heat on different solid metal carbonates.

This is the student’s method.

maths symbol use a spatula to put some metal carbonate in the boiling tube

maths symbol fit the delivery tube into position

maths symbol pour some limewater into the test tube

maths symbol start a timer and immediately begin to heat the metal carbonate

maths symbol record the time when a change first occurs in the limewater

The student repeats the method using different metal carbonates.

When a metal carbonate is heated a reaction sometimes occurs.

The equation for the reaction is

metal carbonate maths symbol metal oxide + carbon dioxide

(a)

State the name given to this type of reaction.

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(b)

State two variables that the student should control in this investigation.

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(c)

Suggest why bubbles appear in the limewater immediately after heating has started but before there is any change to the metal carbonate.

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(d)

Explain the purpose of limewater in this investigation.

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(e)

The table shows some of the results for the student’s investigation.

Metal carbonate Colour change of solid	Time taken for any change in limewater
calcium carbonate remains white	90 seconds
sodium carbonate remains white	no change
copper(II) carbonate	50 seconds

(e)(i)

State the colour change that occurs for copper(II) carbonate.

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(e)(ii)

Give a chemical equation for this reaction of copper(II) carbonate.

[1]

(f)

(f)(i)

There is a relationship between the position of a metal in the reactivity series and how easily the metal carbonate reacts when heated.

Use the student’s results and your own knowledge to deduce this relationship.

[2]

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(f)(ii)

State how you should extend the investigation to see if your deduction is correct.

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Chemistry Paper 1 November 2020, Question 9 12 marks

Also involves Conservation of mass and balanced equations

Sodium hydrogencarbonate (NaHCO₃) is also known as baking soda.

Baking soda can be used to make cakes increase in size in an oven.

This is the equation for the reaction that takes place when baking soda is heated.

$Question 9, shown as an image$

(a)(i)

What type of reaction is this?

$Question 9, shown as an image$

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(a)(ii)

Suggest why the reaction makes the cakes increase in size.

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(b)

A student uses this apparatus to investigate the reaction that takes place when sodium hydrogencarbonate is heated.

This is the student’s method.

● weigh a crucible and record the mass

● add some sodium hydrogencarbonate to the crucible, reweigh it and record the mass

● heat the crucible and contents for five minutes, then allow to cool before weighing and recording the mass

● heat the crucible and contents again for a further three minutes, then allow to cool before weighing and recording the mass

(b)(i)

Give a reason why the crucible and contents are heated for a further three minutes.

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(b)(ii)

The student considered using a lid on the crucible in the experiment.

Suggest an advantage and a disadvantage of using a lid on the crucible.

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(c)

The table shows some of the student’s results.

(c)(i)

Calculate the mass of sodium hydrogencarbonate that the student uses.

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(c)(ii)

Using this equation, calculate the maximum mass of sodium carbonate (Na₂CO₃) that could form in the student’s reaction.

$Question 9, shown as an image$

[M_r of NaHCO₃ = 84 M_r of Na₂CO₃ = 106]

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(d)

In a second experiment, the student uses a larger mass of sodium hydrogencarbonate.

She calculates that she should obtain 4.8 g of sodium carbonate.

She actually obtains 4.2 g of sodium carbonate.

(d)(i)

Calculate the percentage yield from the student’s experiment.

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(d)(ii)

Other than spillages, suggest a possible reason why the student’s actual yield is less than expected.

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Chemistry Paper 1 November 2020 (R), Question 9 11 marks

This question is about some compounds of the elements in Group 4 of the Periodic Table.

(a)

When carbon dioxide dissolves in water, a weak acid forms.

(a)(i)

Which of these could be the pH of this weak acid?

$Question 9, shown as an image$

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(a)(ii)

Which of these is a correct statement about acids?

$Question 9, shown as an image$

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(b)

When lead(II) carbonate is heated, lead(II) oxide and carbon dioxide form.

(b)(i)

Give the name of this type of reaction.

[1]

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(b)(ii)

Complete the equation for this reaction.

[1]

(c)

Silicon dioxide, SiO₂, and silicon(IV) chloride, SiCl₄, are both covalently bonded compounds.

The table shows the melting and boiling points of these two compounds, and the physical state of silicon dioxide at room temperature.

Compound	Melting point in °C	Boiling point in °C	Physical state at room temperature
SiO₂	1710	2230	solid
SiCl₄	−69	58

(c)(i)

Complete the table by giving the physical state of silicon(IV) chloride at room temperature.

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(c)(ii)

Explain, in terms of structure and bonding, why silicon dioxide has a much higher melting point than silicon(IV) chloride.

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Chemistry Paper 1 January 2020, Question 1 6 marks

This question is about gases in the atmosphere.

(a)

The box gives the names of some gases in the atmosphere.

Choose gases from the box to answer these questions.

Each gas may be used once, more than once or not at all.

(a)(i)

Identify a noble gas.

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(a)(ii)

Identify a gas that makes up about 78% of the atmosphere.

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(a)(iii)

Identify a greenhouse gas.

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(a)(iv)

Identify a gas produced by the thermal decomposition of calcium carbonate.

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(b)

Sulfur reacts with oxygen to produce sulfur dioxide gas.

(b)(i)

Write a chemical equation for this reaction.

[1]

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(b)(ii)

State an environmental problem caused when sulfur dioxide gas dissolves in water in the atmosphere.

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Chemistry Paper 2 June 2023, Question 2 Chemistry Paper 2 · June 2023 · Question 2 10 marks

Chemistry Paper 1 January 2023 (R), Question 8 Chemistry Paper 1 · January 2023 (R) · Question 8 12 marks

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Chemistry Paper 1 June 2022, Question 7 Chemistry Paper 1 · June 2022 · Question 7 13 marks

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Chemistry Paper 1 November 2020, Question 9 Chemistry Paper 1 · November 2020 · Question 9 12 marks

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Chemistry Paper 1 June 2022 (R), Question 5 11 marks

Chemistry Paper 1 June 2022, Question 7 13 marks

Chemistry Paper 2 January 2022, Question 2 8 marks

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