Neutralisation

    OCR
    GCSE

    Neutralisation is the exothermic chemical reaction between an acid and a base, resulting in the formation of a salt and water. At the ionic level, this process is defined by the reaction of hydrogen ions from the acid with hydroxide ions from the alkali to produce water molecules. Candidates must demonstrate mastery of general equations for acids reacting with metal oxides, hydroxides, and carbonates, alongside the specific nomenclature for the salts produced. The topic extends to quantitative analysis through titrations, requiring precise calculation of concentrations and volumes.

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    Objectives
    3
    Exam Tips
    4
    Pitfalls
    5
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for identifying neutralisation as the reaction between H+ (aq) and OH- (aq) ions to form water
    • Credit responses that describe the use of a pipette to measure a fixed volume of alkali and a burette for the acid in titrations
    • Award marks for balanced symbol equations where spectator ions are correctly omitted to show the ionic equation
    • For Higher Tier, credit the explanation that strong acids fully ionise in aqueous solution while weak acids only partially ionise

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You have correctly identified the products, but check your state symbols — water is a liquid (l), not aqueous"
    • "Good calculation of moles, but you missed the stoichiometry step — check the ratio of acid to alkali in the equation"
    • "You defined strength correctly, but ensure you distinguish it from concentration; a strong acid can be dilute"
    • "Excellent description of the titration method; to secure the top band, explain how you ensure the results are concordant"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for identifying neutralisation as the reaction between H+ (aq) and OH- (aq) ions to form water
    • Credit responses that describe the use of a pipette to measure a fixed volume of alkali and a burette for the acid in titrations
    • Award marks for balanced symbol equations where spectator ions are correctly omitted to show the ionic equation
    • For Higher Tier, credit the explanation that strong acids fully ionise in aqueous solution while weak acids only partially ionise

    Examiner Tips

    Expert advice for maximising your marks

    • 💡In 6-mark method questions (Level of Response), ensure you specify the apparatus: 'pipette' for the fixed volume and 'burette' for the variable volume
    • 💡When calculating concentration from titration data, always write down the mole ratio from the balanced equation first
    • 💡For Higher Tier, remember the logarithmic nature of pH: a decrease of 1 pH unit corresponds to a 10x increase in H+ concentration

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing the terms 'concentration' (moles per unit volume) and 'strength' (degree of ionisation) when describing acids
    • Failing to include state symbols in ionic equations, particularly incorrectly labelling water as (aq) instead of (l)
    • In titration calculations, forgetting to convert volumes from cm³ to dm³ before calculating moles
    • Stating that a neutral solution contains 'no ions' rather than equal concentrations of H+ and OH- ions

    Key Terminology

    Essential terms to know

    Ionic theory of neutralisation (H+ and OH- interaction)
    General equations for salt formation
    Titration methodology and quantitative analysis
    pH scale and indicator application
    Strong vs Weak acids (Higher Tier)

    Likely Command Words

    How questions on this topic are typically asked

    Describe
    Explain
    Calculate
    Write
    Suggest

    Practical Links

    Related required practicals

    • •{"code":"PAG C3","title":"Titration","relevance":"Technique used to determine the concentration of an acid or alkali via neutralisation"}

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