A-LevelChemistryEquilibriaOct/Nov 2025Paper 1 Q121 Mark
An equilibrium can be represented by the equation shown. P(aq) + Q(aq) ⇌ 2R(aq) + S(aq) In a certain mixture, of volume 1.0 dm³, the equilibrium concentration of Q is 10 mol dm⁻³. What will be the new equilibrium concentration of Q if 5.0 mol of pure Q is completely dissolved in the mixture?
A15 mol dm⁻³
Bbetween 10 mol dm⁻³ and 15 mol dm⁻³
C10 mol dm⁻³
Dbetween 5.0 mol dm⁻³ and 10 mol dm⁻³
✓ Correct Answer
The correct answer is B: between 10 mol dm⁻³ and 15 mol dm⁻³
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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