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Electrolysis Questions and Answers
Free Chemistry Study Cards for GCSE Students
Revise the principles of electrolysis, electrode reactions, half equations and real world applications like the extraction of aluminium with these free Chemistry flashcards.
Question
What is electrolysis?
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Answer
The decomposition of a substance by passing an electric current through it in its molten or aqueous state. Requires an electrolyte (ionic substance) and two electrodes.
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Question
What is an electrolyte?
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Answer
A liquid or solution that conducts electricity by the movement of ions. Must contain free-moving ions — found in molten ionic compounds and aqueous ionic solutions.
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Question
What are electrodes?
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Answer
Conducting rods (usually carbon/graphite or metals) through which current enters and exits the electrolyte. The anode is connected to the positive terminal; the cathode to the negative.
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Question
What happens at the cathode during electrolysis?
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Answer
Reduction occurs — positive ions (cations) move to the cathode and gain electrons. Metals are deposited or hydrogen gas is produced: Cu²⁺ + 2e⁻ → Cu.
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Question
What happens at the anode during electrolysis?
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Answer
Oxidation occurs — negative ions (anions) move to the anode and lose electrons. Oxygen or halogens may be produced: 2Cl⁻ → Cl₂ + 2e⁻.
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Question
What is produced at each electrode when molten NaCl is electrolysed?
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Answer
Cathode: sodium metal (Na⁺ + e⁻ → Na). Anode: chlorine gas (2Cl⁻ → Cl₂ + 2e⁻).
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Question
What is produced at each electrode when aqueous NaCl (brine) is electrolysed?
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Answer
Cathode: hydrogen gas (water is preferentially reduced: 2H₂O + 2e⁻ → H₂ + 2OH⁻). Anode: chlorine gas. The solution becomes sodium hydroxide (NaOH).
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Question
Why is water preferentially reduced at the cathode in dilute solutions?
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Answer
Water has a less negative electrode potential than most metal ions at low concentrations — so water molecules are discharged (reduced) in preference to metals like Na⁺ and K⁺.
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Question
What is electroplating?
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Answer
Using electrolysis to deposit a thin layer of metal onto an object — to improve appearance or prevent corrosion. The object is the cathode; the plating metal is the anode; the electrolyte contains ions of the plating metal.
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Question
How is aluminium extracted industrially?
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Answer
By electrolysis of molten aluminium oxide (Al₂O₃) dissolved in cryolite at ~950°C. Cathode: Al³⁺ + 3e⁻ → Al. Anode: O²⁻ loses electrons, forming O₂ which reacts with the carbon anode.
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