CAIE A Level Chemistry 9701 · Equilibria
A student has three dilute aqueous solutions:
The student measures the pH of each solution using a pH meter. The student also adds a piece of magnesium ribbon to each solution.
(a) Explain why the pH of solution X is lower than the pH of solution Y. (b) Explain why the reaction of magnesium with solution X is faster than with solution Y. (c) Explain, using Brønsted–Lowry theory, why solution Z has a pH greater than 7.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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