Practical Electrolysis — Past Paper Exam
Cambridge IGCSE Chemistry (0620) · Experimental Design & Observation
Electrolysis of CuSO₄(aq) — copper deposits at cathode, O₂ at anode
The electrolysis of molten lead(II) bromide must be carried out in a fume cupboard. Give two reasons for this safety precaution.
During electrolysis of dilute sulfuric acid, hydrogen gas is produced at the cathode. State TWO safety precautions that must be taken when collecting this gas.
Concentrated sodium hydroxide solution is used as the electrolyte in one experiment. State the hazard symbol associated with this substance and explain why it is hazardous.
A student wishes to electrolyse molten lead(II) bromide. Describe TWO safety precautions the student must take before starting the experiment.
During electrolysis of copper(II) sulfate solution, copper sulfate is described as harmful. State what is meant by harmful and give ONE precaution a student should take when handling it.
State THREE observations made during the electrolysis of concentrated aqueous copper(II) chloride solution.
Describe what is observed at each electrode during the electrolysis of molten lead(II) bromide. Include the substance produced at each electrode.
During electrolysis of dilute sulfuric acid with platinum electrodes, gas is produced at both electrodes. State the observation at each electrode and identify the volume ratio of gases collected.
A student electrolyses copper(II) sulfate solution using copper electrodes (not inert). State THREE observations the student would make during this experiment.
State what is observed when the electrolysis of concentrated sodium chloride solution is carried out with graphite electrodes. Identify the product at each electrode.
Describe how you would test the gas produced at the ANODE during electrolysis of concentrated sodium chloride solution. State the result of a positive test.
A student collects a gas at the cathode during electrolysis of dilute sulfuric acid. Describe how the student could test the gas and state the expected result.
Suggest ONE improvement to the basic electrolysis apparatus to make the experiment more quantitative, and explain how this improvement helps.
A student electrolyses copper(II) sulfate solution to copper-plate a metal spoon. Describe the experimental design: state which electrode is the spoon, what the electrolyte should be, and explain what happens at the molecular level at the spoon during the process.
Plan an experiment to compare the masses of copper deposited at the cathode when different currents are passed through copper(II) sulfate solution for the same length of time. Your plan should include: the variables controlled, the measurements taken, and how the results would be presented.
⚡ Electrolysis — Golden Rules
Cathode (−): Reduction · Gains electrons · Metal/H₂
Anode (+): Oxidation · Loses electrons · Cl₂/O₂/Br₂
Dilute vs Conc: Concentration determines which ion is discharged at anode
Cl₂ test: Damp blue litmus → bleaches white
H₂ test: Lighted splint → squeaky pop
O₂ test: Glowing splint → relights
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