AQA · GCSE · Chemistry

    Course version: 8462 · Version from Sept 2018

    At the anode (positive electrode), negatively charged ions lose electrons…

    Full specification wording

    Representation of reactions at electrodes as half equations (HT only): At the anode (positive electrode), negatively charged ions lose electrons and so the reactions are oxidations.

    At the anode, which is the positive electrode, negatively charged ions move towards it because opposite charges attract.

    Checked against the AQA 8462 specification (opens in a new tab) on .

    • Point 2 of 2
    • 3 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    At the anode, which is the positive electrode, negatively charged ions move towards it because opposite charges attract. Each negative ion loses one or more electrons to the electrode and becomes a neutral atom or molecule. Losing electrons is oxidation, so every anode reaction in electrolysis is an oxidation. For example, in copper chloride solution, chloride ions are oxidised: 2Cl⁻(aq) → Cl₂(g) + 2e⁻. In dilute sulfuric acid, hydroxide ions are oxidised: 4OH⁻(aq) → O₂(g) + 2H₂O(l) + 4e⁻. You show this by writing a balanced half equation with correct charges and state symbols, and higher-tier questions assess whether you can construct and interpret such equations.

    What earns the marks

    • State that the anode is the positive electrode and that negative ions move towards it.
    • Explain that negative ions lose electrons at the anode and that electron loss is oxidation.
    • Write a balanced anode half equation showing the ion, product and electrons with correct formulae and state symbols.
    • Balance the number of electrons lost with the charge on the ions, for example two chloride ions lose two electrons to form one chlorine molecule.
    • Link the anode half equation to the overall electrolysis reaction and to the product observed.

    Common mistakes and how to put them right

    • Writing the anode as the negative electrode.

      Put it right by remembering that the anode is positive and attracts negative ions.

    • Showing electrons gained at the anode.

      Put it right by writing electrons as lost, for example 2Cl⁻(aq) → Cl₂(g) + 2e⁻.

    • Forgetting to balance atoms and charge in the half equation.

      Put it right by checking that atoms and total charge are equal on both sides.

    Exam tips

    • Check the charge balance: the total charge on the left must equal the total charge on the right.
    • Use the phrase lose electrons equals oxidation to justify why an anode reaction is an oxidation.
    • Include state symbols in half equations because they show the form of each substance.

    Try the lesson

    The start of the Representation of reactions at electrodes as half equations (HT only): At the anode (positive electrode), negatively charged ions lose electrons and so the reactions are oxidations. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which half equation correctly represents the oxidation of chloride ions at the anode during electrolysis?

    Listen

    At the anode, which is the positive electrode, negatively charged ions move towards it because opposite charges attract. Each negative ion loses one or more electrons to the electrode and becomes a neutral atom or molecule. Losing electrons is oxidation, so every anode reaction in electrolysis is an oxidation. For example, in copper chloride solution, chloride ions are oxidised: 2Cl⁻(aq) → Cl₂(g) + 2e⁻. In dilute sulfuric acid, hydroxide ions are oxidised: 4OH⁻(aq) → O₂(g) + 2H₂O(l) + 4e⁻. You show this by writing a balanced half equation with correct charges and state symbols, and higher-tier questions assess whether you can construct and interpret such equations. A strong answer earns marks for these points. State that the anode is the positive electrode and that negative ions move towards it. Explain that negative ions lose electrons at the anode and that electron loss is oxidation. Write a balanced anode half equation showing the ion, product and electrons with correct formulae and state symbols. Balance the number of electrons lost with the charge on the ions, for example two chloride ions lose two electrons to form one chlorine molecule. A common slip: Writing the anode as the negative electrode. Instead, remembering that the anode is positive and attracts negative ions. Exam tip: Check the charge balance: the total charge on the left must equal the total charge on the right.

    See it

    A top-down flowchart with seven boxes. The first box says the anode is the positive electrode and points to a second box saying negatively charged ions move towards the anode. That points to a third box saying negative ions lose electrons to the electrode. The third box points to a fourth box saying losing electrons is oxidation, which points to a fifth box saying anode reactions are oxidations. The third box also points to a sixth box saying balanced half equation with state symbols, which points to a seventh box saying check atoms and total charge balance.
    Shows how negative ions moving to the positive anode, losing electrons and being oxidised leads to a balanced anode half equation.

    Key words

    Say what each word means before you turn the card.

    Balanced half equation

    Try answering aloud or in your head before turning the card.

    Anode

    Try answering aloud or in your head before turning the card.

    State symbols

    Try answering aloud or in your head before turning the card.

    See every definition
    Balanced half equation
    An equation showing the ion, product and electrons with correct formulae and state symbols, balanced so atoms and total charge are equal on both sides.
    Anode
    The positive electrode, towards which negatively charged ions move because opposite charges attract.
    State symbols
    Symbols included in half equations because they show the form of each substance.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart with seven boxes. The first box says the anode is the positive electrode and points to a second box saying negatively charged ions move towards the anode. That points to a third box saying negative ions lose electrons to the electrode. The third box points to a fourth box saying losing electrons is oxidation, which points to a fifth box saying anode reactions are oxidations. The third box also points to a sixth box saying balanced half equation with state symbols, which points to a seventh box saying check atoms and total charge balance.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

    There is more to this lesson

    The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.

    Carry on with the full lesson

    A week of Premium from your first lesson · Then the free plan continues · No card, no charge

    Test your understanding of Representation of reactions at electrodes as half equations (HT only): At the anode (positive electrode), negatively charged ions lose electrons and so the reactions are oxidations.

    Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.

    Take topic quiz

    A week of Premium from your first lesson · Then the free plan continues · No card, no charge

    Start free

    Cookies on MasteryMind

    Essential cookies keep you signed in.

    Analytics and advertising cookies stay off unless you accept.

    Read our Privacy Policy.