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Chemical Changes

Electrolysis of aqueous solutions

  • 3 things to know
  • Chemistry Paper 1

Overview

Which ions are present in a solution, how relative reactivity decides whether the metal or hydrogen forms at the cathode, when oxygen or a halogen forms at the anode, predicting products, and testing the gases collected.

What you need to know

Answer each one before you reveal it.

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Key term

Explain which ions are present when an ionic compound is electrolysed in solution and what forms at the cathode for copper sulfate and sodium chloride.

Key term

What decides which ions are discharged when a solution is electrolysed with inert electrodes?

Key term

Which ions are present in a solution made by dissolving a single ionic compound in water?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What decides which ions are discharged when a solution is electrolysed with inert electrodes?

    Model answer

    The relative reactivity of the elements whose ions are present.

  2. 2

    Which ions are present in a solution made by dissolving a single ionic compound in water?

    Model answer

    The positive and negative ions of the compound, together with hydrogen ions and hydroxide ions from the water.

  3. 3

    Why can electrolysing a solution give different products from electrolysing the same compound molten?

    Model answer

    In solution the water also supplies ions, so hydrogen or oxygen may be discharged instead of the compound's own ions.

  4. 4

    What is formed at the cathode when the metal in the dissolved compound is more reactive than hydrogen?

    Model answer

    Hydrogen gas.

  5. 5

    Predict the product at the cathode when copper sulfate solution is electrolysed, and explain why.

    Model answer

    Copper, because copper is less reactive than hydrogen so its ions are discharged.

  6. 6

    Predict the product at the cathode when sodium chloride solution is electrolysed, and explain why.

    Model answer

    Hydrogen, because sodium is more reactive than hydrogen so the sodium ions stay in solution.

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