www.intellectualthinking.com

Tag: Electrolysis

  • Electrolysis Explained for GCSE Students

    Electrolysis Explained for GCSE Students

    Definition of electrolysis

    Electrolysis is the breaking down of an electrolyte using an applied electric current.

    An electrolyte is an ionic substance that has been dissolved in a solvent or has been melted.

    Electrolysis of molten compounds

    The ionic compound is heated to a very high temperature until it reaches liquid state. The metal cations are positively charged metal ions. They will move towards the negatively charged electrode, called a cathode. These ions become metal atoms at the cathode.

    The non-metal anions are negatively charged ions. They will move towards the positively charged electrode, called an anode. These ions become non-metal atoms at the anode.

    Fig.1 – electrolysis of molten lead (II) bromide

    Diagram showing the electrolysis of molten lead(II) bromide, including a DC power supply, positive lead ions attracted to the negative electrode, and negative bromide ions attracted to the positive electrode.

    Electrolysis of aqueous solutions

    The ionic compound is dissolved in water. In water, there are H+ and OH– ions existing and they will compete with the metal cations and non-metal anions.

    Fig.2 – electrolysis of aqueous copper sulfate

    Diagram illustrating a copper electrolysis setup showing an anode, cathode, and copper(II) sulphate solution, with reactions for oxygen gas production and copper metal deposition.

    Half-equations explained

    To figure out what is produced at the cathode (negative electrode) and at the anode (positive electrode), follow the two rules below:

    Rule 1: At the cathode, check the reactivity of the metal ion. If it is more reactive than hydrogen, the hydrogen ions are reduced to form a hydrogen molecule.

    Chart showing metals arranged by reactivity, from most reactive potassium at the top to least reactive gold at the bottom.

    Rule 2: At the anode, the anions are oxidised in the following order:

    Halide ion > hydroxide ion > all other negatively charged ions

    Table showing negative ions from electrolytes and the corresponding elements released at the anode.

    If there are no halide ions present to be oxidised at the anion, then the hydroxide ions are next to be oxidised and the following half-equation describes what happens to the hydroxide ion that is oxidised at the anode:

    4OH– → 2H2O + O2 + 4e–

    Practice questions

    A worksheet on electrolysis and metal extraction, featuring multiple choice and table completion questions about molten substances, electrode products, and balancing a chemical equation.
    A chemistry exam question focusing on the calculation of the relative formula mass of aluminium oxide and a diagram illustrating the reactivity series of metals, including potassium, lithium, carbon, zinc, tin, and gold, with instructions for predicting extraction methods.

    Source for Questions papers and Answers:

    AQA GCSE Chemistry Topic 4: Chemical Changes Revision – PMT

    Answers to practice questions:

    A mark scheme for an exam question on electrolysis, detailing the movement of ions, products at electrodes, and calculations related to electrochemical processes.