A-LevelChemistryEquilibriaOct/Nov 2010Paper 1 Q111 Mark
A dimer, X, is stable when solid but a dynamic equilibrium is set up in solution. X(aq) ⇌ 2Y(aq) A solution of X has an initial concentration of 0.50 mol dm⁻³. When equilibrium has been reached [X(aq)] has fallen to 0.25 mol dm⁻³. The changes in [X(aq)] and [Y(aq)] are plotted against time until equilibrium is reached. The value of K_c is then calculated. Which graph and value for K_c are correct?
A[Graph A showing [X] decreasing from 0.50 to 0.25 and [Y] increasing from 0 to 0.50, with Kc = 1]
B[Graph B showing [X] decreasing from 0.50 to 0.25 and [Y] increasing from 0 to 0.25, with Kc = 2]
C[Graph C showing [X] decreasing from 0.50 to 0.25 and [Y] increasing from 0 to 0.50, with Kc = 1]
D[Graph D showing [X] decreasing from 0.50 to 0.25 and [Y] increasing from 0 to 0.25, with Kc = 2]
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The correct answer is C. This question tests the candidate's understanding of equilibria within the Chemistrysyllabus. The examiner's mark scheme requires...
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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...
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