Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Electrolysis
198 practice questions
Topics covered
- Why things conduct electricity17 practice questions
- Passing electricity through compounds: electrolysis20 practice questions
- The electrolysis of molten compounds19 practice questions
- Electrolysis and redox19 practice questions
- The electrolysis of other molten substances19 practice questions
- The electrolysis of aqueous solutions18 practice questions
- The electrolysis of sodium chloride solution19 practice questions
- The electrolysis of copper(ii) sulfate solution using inert electrodes18 practice questions
- The electrolysis of some other solutions using inert electrodes19 practice questions
- What would happen with non-electrolytes?19 practice questions
Practice questions
191–198 of 198
Question 191
5 marks · Easy
Answer and see the solution →A student investigates the electrolysis of two different substances using graphite electrodes:
(a)[2 marks]Molten lead(II) bromide (PbBr₂) is electrolysed. Predict which element forms at the cathode and which at the anode. Explain how you know.
(b)The student now electrolyses concentrated aqueous magnesium chloride (MgCl₂(aq)). After testing the gases, they find the volume of chlorine gas collected at the anode is much less than the volume of hydrogen collected at the cathode.
(i)[1 mark]Explain why hydrogen, and not magnesium, is formed at the cathode.
(ii)[2 marks]Give a reason why less chlorine gas is collected at the anode than expected.
Question 192
6 marks · Normal
Answer and see the solution →Potassium iodide (KI) is an ionic compound. When heated until molten and electrolysed using inert electrodes, iodine gas is produced at one electrode and potassium metal at the other.
(a)[1 mark]State the ions present in molten potassium iodide.
(b)[1 mark]Write the half-equation for the reaction occurring at the cathode.
(c)[1 mark]Write the half-equation for the reaction occurring at the anode.
(d)[2 marks]State, in terms of electron transfer, which reaction involves reduction and which involves oxidation.
(e)[1 mark]Explain how you can use the mnemonic OILRIG to identify which reaction at the electrodes is oxidation and which is reduction.
Question 193
6 marks · Normal
Answer and see the solution →A student carries out the electrolysis of molten calcium chloride (CaCl2) in a laboratory using inert carbon electrodes.
(a)[2 marks]State what is meant by 'discharging an ion' during electrolysis.
(b)[1 mark]Identify the ions in molten calcium chloride and their movement during electrolysis.
(c)[1 mark]Write the half-equation for the discharge of chloride ions at the anode.
(d)[2 marks]Explain, using electron transfer, what happens to a calcium ion during electrolysis.
Question 194
6 marks · Normal
Answer and see the solution →A student sets up an electrolysis experiment using molten potassium iodide (KI). An external circuit with a bulb lights up when the current is switched on.
(a)[2 marks]State the ions present in molten potassium iodide. Identify which ions move towards the cathode and which move towards the anode during electrolysis.
(b)[1 mark]Write the ionic half-equation for the reaction occurring at the cathode.
(c)[1 mark]Write the ionic half-equation for the reaction occurring at the anode.
(d)[2 marks]For the electrode reaction at the cathode, state whether it is an oxidation or a reduction. Justify your answer using the concept of electron transfer.
Question 195
6 marks · Normal
Answer and see the solution →During the electrolysis of molten calcium chloride (CaCl2), calcium forms at one electrode and chlorine gas is released at the other.
(a)[2 marks]Write the balanced ionic half-equation for the reaction at the electrode where chlorine gas is produced.
(b)[2 marks]Explain what is meant by the term 'discharging an ion' using Ca^2+ or Cl^- as an example from this electrolysis process.
(c)[2 marks]Recall the meaning of the mnemonic OILRIG and use it to decide whether the reaction at the chlorine-producing electrode is an oxidation or a reduction.
Question 196
7 marks · Hard
Answer and see the solution →A science teacher asks students to compare what happens at the cathode during the electrolysis of sodium chloride solution and copper(II) sulfate solution, both using inert electrodes.
(a)[3 marks]Explain why the solution around the cathode becomes alkaline during the electrolysis of sodium chloride solution.
(b)[2 marks]Explain why copper is deposited at the cathode instead of hydrogen during the electrolysis of copper(II) sulfate solution using inert electrodes.
(c)[2 marks]In both electrolysis experiments above, water is present in solution. State one difference in the effect of prolonged electrolysis on the composition of the solution in each case, and explain your answer using the relevant ions.
Question 197
7 marks · Hard
Answer and see the solution →A student investigates the products formed at the cathode when electrolysing sodium chloride solution and copper(II) sulfate solution, each with inert electrodes.
(a)[1 mark]State the product formed at the cathode during the electrolysis of sodium chloride solution using inert electrodes.
(b)[2 marks]Explain why hydrogen, not sodium, is produced at the cathode during the electrolysis of sodium chloride solution.
(c)[1 mark]State the product formed at the cathode during the electrolysis of copper(II) sulfate solution using inert electrodes.
(d)[2 marks]Explain why copper is deposited at the cathode during the electrolysis of copper(II) sulfate solution with inert electrodes.
(e)[1 mark]In both experiments, describe one observation that could be made at the cathode, and explain how it relates to the product formed.
Question 198
7 marks · Hard
Answer and see the solution →Electrolysis of sodium chloride solution and copper(II) sulfate solution can be represented by balanced half-equations.
(a)[2 marks]Write a balanced half-equation for the reaction at the cathode during electrolysis of sodium chloride solution.
(b)[1 mark]Write a balanced half-equation for the reaction at the anode during electrolysis of sodium chloride solution.
(c)[2 marks]Write a balanced half-equation for the reaction at the cathode during electrolysis of copper(II) sulfate solution using inert electrodes.
(d)[2 marks]Write a balanced half-equation for the reaction at the anode during electrolysis of copper(II) sulfate solution using inert electrodes.