Metal Oxides

    OCR
    GCSE

    Metal oxides are ionic compounds formed via the oxidation of metals, defined fundamentally as the gain of oxygen or the loss of electrons. These compounds typically exhibit basic character, reacting with acids to produce salts and water, although specific examples such as aluminium oxide display amphoteric properties. The thermal stability of the oxide lattice determines the energy required for reduction, directly linking the reactivity series to industrial extraction methods such as reduction with carbon or electrolysis. Mastery of this topic requires integrating concepts of redox, periodicity, and stoichiometric calculations.

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    Objectives
    3
    Exam Tips
    3
    Pitfalls
    4
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that metal oxides act as bases which neutralise acids to produce a salt and water
    • Credit the correct balanced symbol equation, ensuring the salt formula corresponds to the metal valency (e.g., CuO + H₂SO₄ → CuSO₄ + H₂O)
    • Award marks for describing the purification method: adding oxide in excess, filtering to remove unreacted solid, and heating the filtrate to the point of crystallisation
    • Credit the definition of oxidation as the gain of oxygen when a metal reacts to form its oxide

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the products, but check your salt formula — does the charge of the metal ion balance the anion?"
    • "Good description of the method, but you missed the critical step of adding the oxide 'in excess'. Why is this necessary for safety?"
    • "You have written the word equation correctly. To access higher marks, convert this into a balanced symbol equation including state symbols."
    • "Excellent link between the basic nature of the oxide and the neutralisation reaction. Now consider how you would prove the final salt is pure."

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that metal oxides act as bases which neutralise acids to produce a salt and water
    • Credit the correct balanced symbol equation, ensuring the salt formula corresponds to the metal valency (e.g., CuO + H₂SO₄ → CuSO₄ + H₂O)
    • Award marks for describing the purification method: adding oxide in excess, filtering to remove unreacted solid, and heating the filtrate to the point of crystallisation
    • Credit the definition of oxidation as the gain of oxygen when a metal reacts to form its oxide

    Examiner Tips

    Expert advice for maximising your marks

    • 💡In 6-mark practical questions, structure your answer chronologically: Reaction (add excess/heat) → Filtration (remove solid) → Crystallisation (evaporate/cool/dry)
    • 💡Always check the oxidation state of the metal (e.g., Iron(III) vs Iron(II)) when writing the formula for the resulting salt
    • 💡Use state symbols correctly in equations; remember metal oxides are usually solids (s) and the resulting salts are aqueous (aq) before crystallisation

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Describing the evaporation step incorrectly by suggesting 'evaporate to dryness' for hydrated crystals, which removes water of crystallisation and produces anhydrous powder
    • Failing to specify that the metal oxide must be added 'in excess' to ensure all the acid is neutralised, leaving dangerous acidic residues
    • Incorrectly identifying the products of the reaction, often omitting water or writing the wrong formula for the salt (e.g., NaO instead of Na₂O)

    Key Terminology

    Essential terms to know

    Oxidation and Reduction (Oxygen transfer and electron transfer)
    Reactivity Series and Metal Extraction methods
    Acid-Base Character (Basic vs Amphoteric oxides)
    Conservation of Mass in chemical reactions

    Likely Command Words

    How questions on this topic are typically asked

    Describe
    Explain
    Write
    Calculate
    Suggest

    Practical Links

    Related required practicals

    • •{"code":"PAG C1","title":"Preparation of a pure, dry sample of a soluble salt from an insoluble oxide","relevance":"Direct application of metal oxide neutralisation"}

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