4.4.3

Electrolysis of Aqueous Solutions & Half Equations

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Electrolysis of Aqueous Solutions

The products of the electrolysis of aqueous solutions are difficult to predict because the water molecules in the solution split up to give hydrogen (H+) and hydroxide (OH-) ions.

Illustrative background for At the anode (positive electrode)Illustrative background for At the anode (positive electrode) ?? "content

At the anode (positive electrode)

  • What is formed at the anode depends on if there are halide ions present:
    • If there are halide ions present, the respective halogen forms.
    • If there are no halide ions, oxygen forms.
Illustrative background for At the cathode (negative electrode)Illustrative background for At the cathode (negative electrode) ?? "content

At the cathode (negative electrode)

  • What is formed at the cathode depends on the reactivity of the metal:
    • Hydrogen is produced if the metal is higher than hydrogen in the reactivity series.
    • The metal is produced if the metal is lower than hydrogen in the reactivity series.

Half Equations

During electrolysis, different reactions take place at the different electrodes. The reactions that happen at each electrode can be shown using half equations. The electrolysis of lead bromide is an example of this:

Illustrative background for At the anode (positive electrode)Illustrative background for At the anode (positive electrode) ?? "content

At the anode (positive electrode)

  • Oxidation reactions happen i.e. negatively charged ions lose electrons.
    • 2Br- → Br2 + 2e-
Illustrative background for At the cathode (negative electrode)Illustrative background for At the cathode (negative electrode) ?? "content

At the cathode (negative electrode)

  • Reduction reactions happen i.e. positively charged ions gain electrons.
    • Pb2+ + 2e- → Pb

Jump to other topics

1Atomic Structure

2Chemical Bonding

3Quantitative Chemistry

4Chemical Changes

5Energy Changes

6The Rate & Extent of Chemical Change

7Organic Chemistry

8Chemical Analysis

9Chemistry of the Atmosphere

10Using Resources

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