Extracting Metals

    OCR
    GCSE

    The extraction of metals is fundamentally dictated by the position of the metal in the reactivity series, which determines whether reduction with carbon or electrolysis is required. Candidates must understand that metals less reactive than carbon are extracted by heating their oxides with carbon, a process defined as reduction through the loss of oxygen. Conversely, metals more reactive than carbon require electrolysis of molten compounds, necessitating an understanding of energy demands and electron transfer. The topic extends to sustainable development, requiring evaluation of biological extraction methods like phytomining and bioleaching, alongside the economic and environmental importance of recycling.

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    Objectives
    4
    Exam Tips
    4
    Pitfalls
    5
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that metals above carbon in the reactivity series must be extracted by electrolysis of the molten ore
    • Credit responses that identify carbon monoxide (CO) as the primary reducing agent in the blast furnace, not just carbon
    • Award 1 mark for explaining that cryolite is added to bauxite to lower the melting point and reduce energy costs
    • Candidates must describe phytoextraction as the absorption of metal ions by plant roots, followed by burning to produce ash containing metal compounds
    • Credit correct half-equations at the anode (2O²⁻ → O₂ + 4e⁻) and cathode (Al³⁺ + 3e⁻ → Al) for aluminium extraction

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the method, but you must explain *why* based on the reactivity series position relative to carbon"
    • "Your equation is balanced, but check your state symbols—remember the aluminium oxide is molten, not aqueous"
    • "Good description of bioleaching. To access higher marks, contrast the low energy cost with the slow rate of reaction"
    • "You mentioned the anode wears away—now explain the chemical reaction causing this (C + O₂ → CO₂)"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that metals above carbon in the reactivity series must be extracted by electrolysis of the molten ore
    • Credit responses that identify carbon monoxide (CO) as the primary reducing agent in the blast furnace, not just carbon
    • Award 1 mark for explaining that cryolite is added to bauxite to lower the melting point and reduce energy costs
    • Candidates must describe phytoextraction as the absorption of metal ions by plant roots, followed by burning to produce ash containing metal compounds
    • Credit correct half-equations at the anode (2O²⁻ → O₂ + 4e⁻) and cathode (Al³⁺ + 3e⁻ → Al) for aluminium extraction

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When evaluating extraction methods, explicitly compare energy requirements (electricity vs. heat) and environmental impact (CO₂ emissions vs. landscape scarring)
    • 💡Memorize the position of Carbon and Hydrogen in the reactivity series; this is the key discriminator for choosing reduction or electrolysis
    • 💡In 6-mark Level of Response questions about biological methods, structure your answer into: Process Description → Advantages (low energy/mining waste) → Disadvantages (slow/low yield)
    • 💡Always include state symbols in electrolysis equations, specifically noting the electrolyte is molten (l)

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that cryolite acts as a catalyst; examiners require reference to lowering the melting point or operating temperature
    • Confusing the reduction of iron oxide with the combustion of coke; students often fail to show the step where CO reduces Fe₂O₃
    • Assuming biological extraction methods are faster or more efficient than traditional mining; failing to acknowledge they are slow and weather-dependent
    • Forgetting that the graphite anodes in aluminium extraction must be replaced periodically because they react with oxygen to form carbon dioxide

    Key Terminology

    Essential terms to know

    Reactivity series as the determinant of extraction method
    Reduction of metal oxides with carbon
    Electrolysis of molten ores for high-reactivity metals
    Biological extraction methods (Phytomining and Bioleaching)
    Life Cycle Assessment (LCA) and recycling economics

    Likely Command Words

    How questions on this topic are typically asked

    Explain
    Predict
    Evaluate
    Write
    Compare
    Calculate

    Practical Links

    Related required practicals

    • •{"code":"PAG C1","title":"Electrolysis of aqueous solutions","relevance":"Principles of ion movement and discharge apply to industrial extraction"}
    • •{"code":"Investigation","title":"Displacement reactions","relevance":"Establishing the reactivity series order to determine extraction method"}

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