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Electrolysis of molten ionic compounds

Edexcel IGCSE Chemistry

Topic questions Chemical changes Electrolysis of molten ionic compounds

Electrolysis of molten ionic compounds

6 questions · 72 marks · about 1.5 hours

Electrolysis of molten ionic compounds questions

TopicElectrolysis of molten ionic compounds

Chemistry Paper 2 June 2024, Question 6 14 marks

A scientist reacts lead(II) nitrate solution with sodium bromide solution.

This is the equation for the reaction.

Pb(NO₃)₂(aq) + 2NaBr(aq) maths symbol PbBr₂(s) + 2NaNO₃(aq)

(a)

Describe how the scientist could obtain a pure dry sample of lead(II) bromide (PbBr₂) from the reaction mixture.

[3]

Reveal mark scheme

(b)

The scientist reacts an excess of lead(II) nitrate solution with 25 cm³ of sodium bromide solution of concentration 2.0 mol/dm³.

(b)(i)

Show that the amount of sodium bromide used is 0.050 mol.

[1]

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(b)(ii)

Show that the maximum theoretical mass of lead(II) bromide is approximately 9 g.

[for PbBr₂ M_r = 367]

[2]

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(c)

The scientist electrolyses molten lead(II) bromide using this apparatus.

(c)(i)

Explain why lead(II) bromide needs to be molten rather than solid for electrolysis to occur.

[3]

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(c)(ii)

The electrolyte is at a temperature of 400 maths symbol C.

Explain a suitable material for the electrodes.

[2]

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(c)(iii)

Give the half‑equation that occurs at the negative electrode.

[1]

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(d)

Bromine forms at the positive electrode.

This is the half‑equation for the reaction at the positive electrode.

$Question 6, shown as an image$

(d)(i)

State what is observed at the positive electrode.

[1]

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(d)(ii)

State why the half‑equation represents an oxidation reaction.

[1]

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Chemistry Paper 2 November 2023, Question 7 14 marks

(a)

Sodium chloride is an ionic compound.

Explain why sodium chloride conducts electricity when it is molten or in solution, but not when it is solid.

[2]

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(b)

A solution of sodium chloride can be electrolysed using this apparatus.

(b)(i)

If the solution is dilute, a significant amount of oxygen collects at P.

Complete the ionic half-equation for this reaction.

$Question 7, shown as an image$

[1]

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(b)(ii)

If the solution is concentrated, chlorine is the main product that collects at P.

This is the ionic half-equation for the reaction.

$Question 7, shown as an image$

State why this is an oxidation reaction.

[1]

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(c)

The gas that collects at Q is hydrogen.

(c)(i)

Give a test for hydrogen.

[1]

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(c)(ii)

Explain how hydrogen gas forms at the negative electrode.

[3]

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(d)

Hydrogen reacts with oxygen to form water.

The equation shows the covalent bonds in the molecules.

$Question 7, shown as an image$

The table gives the bond energies.

Bond	H H	O O	O H
Bond energy in kJ / mol	436	498	463

(d)(i)

Use the equation and the values in the table to calculate the enthalpy change, Δ H, for the reaction.

Include a sign in your answer.

[3]

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(d)(ii)

Complete the diagram to show the energy levels of the reactants and products, and the enthalpy change, Δ H.

[3]

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Chemistry Paper 2 January 2023, Question 5 11 marks

This question is about metals.

(a)

Explain why metals are malleable.

[2]

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(b)

(b)(i)

Explain why molten sodium chloride conducts electricity.

[2]

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(b)(ii)

Explain how sodium metal forms at the negative electrode.

[2]

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(b)(iii)

Write an ionic half-equation for the formation of chlorine gas at the positive electrode.

[1]

(b)(iv)

Give a reason why sodium metal does not form in the electrolysis of an aqueous solution of sodium chloride.

[1]

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(c)

Copper can be produced by reacting an oxide of copper with methane.

The diagram shows the apparatus used.

The oxide of copper is heated until the reaction is complete.

The table shows the results.

	Mass in g
empty weighing boat	17.25
weighing boat + oxide of copper	22.02
weighing boat + copper	21.06

Use the results to show that this oxide has the empirical formula CuO

[for Cu, A_r = 63.5 for O, A_r = 16]

[3]

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Chemistry Paper 2 January 2022 (R), Question 6 12 marks

A teacher prepares the insoluble salt lead(II) bromide (PbBr₂) by mixing solutions of lead(II) nitrate and sodium bromide.

(a)

Describe what the teacher should do next to obtain a pure, dry sample of lead(II) bromide.

[3]

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(b)

The teacher then sets up a circuit in a fume cupboard using the pure, dry sample of lead(II) bromide.

Explain why the lamp does not light when the lead(II) bromide is solid.

[2]

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(c)

The teacher heats the lead(II) bromide.

When the lead(II) bromide is molten, the lamp lights and bromine forms at the positive electrode.

(c)(i)

State what observation would be made at the positive electrode.

[1]

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(c)(ii)

Explain how bromide ions in the molten lead(II) bromide become bromine molecules at the positive electrode.

[4]

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(d)

Write an ionic half-equation for the reaction that occurs at the negative electrode.

Include state symbols in your equation.

[2]

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Chemistry Paper 2 January 2021, Question 5 14 marks

This question is about the metal aluminium.

(a)

Aluminium is malleable and conducts electricity.

The diagram shows the arrangement of the ions in aluminium metal.

$Question 5, shown as an image$

(a)(i)

Explain why aluminium is malleable.

[2]

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(a)(ii)

Explain why aluminium conducts electricity.

[2]

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(b)

Aluminium cannot be extracted by heating a mixture of carbon and aluminium oxide.

Give a reason why heating a mixture of aluminium oxide and carbon does not produce aluminium.

[1]

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(c)

Aluminium is extracted industrially by the electrolysis of molten aluminium oxide Al₂O₃ at a temperature of about 950 °C.

Aluminium metal forms at the negative electrode and oxygen gas forms at the positive electrode. The positive and negative electrodes are made of graphite.

The diagram shows the apparatus used.

(c)(i)

Explain how aluminium metal forms at the negative electrode.

[2]

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(c)(ii)

Write an ionic half-equation for the formation of oxygen gas at the positive electrode.

[1]

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(c)(iii)

Suggest why carbon dioxide gas is also produced at the positive electrode.

[2]

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(d)

Aluminium reacts with iron(III) oxide. The reaction is exothermic.

The equation for the reaction is

$Question 5, shown as an image$

(d)(i)

State how the equation shows that iron(III) oxide is reduced.

[1]

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(d)(ii)

Draw an energy level diagram for the reaction between aluminium and iron(III) oxide.

[3]

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Chemistry Paper 2 January 2020 (R), Question 4 7 marks

This question is about the metal, lead.

(a)

Explain why metals, such as lead, are malleable.

[2]

Reveal mark scheme

(b)

A teacher uses this apparatus in a fume cupboard to demonstrate the electrolysis of lead(II) bromide.

The lead(II) bromide is heated until it melts.

When the lead(II) bromide melts, the lamp lights.

One of the products of this electrolysis is lead.

(b)(i)

State why solid lead(II) bromide does not conduct electricity.

[1]

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(b)(ii)

Bromine is formed by the oxidation of bromide ions at the positive electrode.

Complete the ionic half-equation for the oxidation of bromide ions.

$Question 4, shown as an image$

[1]

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(b)(iii)

Explain why lead metal forms at the negative electrode.

[2]

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(b)(iv)

The teacher stops heating the mixture and allows it to solidify.

Suggest why the lamp stays alight.

[1]

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Electrolysis of molten ionic compounds

Electrolysis of molten ionic compounds questions

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Chemistry Paper 2 January 2023, Question 5 Chemistry Paper 2 · January 2023 · Question 5 11 marks

Chemistry Paper 2 January 2022 (R), Question 6 Chemistry Paper 2 · January 2022 (R) · Question 6 12 marks

Chemistry Paper 2 January 2021, Question 5 Chemistry Paper 2 · January 2021 · Question 5 14 marks

Chemistry Paper 2 January 2020 (R), Question 4 Chemistry Paper 2 · January 2020 (R) · Question 4 7 marks

Certified Chemistry memes. Peer-reviewed by nobody.

Chemistry Paper 2 June 2024, Question 6 14 marks

Chemistry Paper 2 November 2023, Question 7 14 marks

Chemistry Paper 2 January 2023, Question 5 11 marks

Chemistry Paper 2 January 2022 (R), Question 6 12 marks

Chemistry Paper 2 January 2021, Question 5 14 marks

Chemistry Paper 2 January 2020 (R), Question 4 7 marks