CAIE A Level Chemistry 9701 · Chemistry of transition elements
An aqueous solution of copper(II) sulfate is pale blue. When concentrated hydrochloric acid is added, the solution turns yellow-green. Explain, in terms of d orbital splitting and electron transitions, why the aqueous copper(II) ion is coloured and why the colour changes when concentrated hydrochloric acid is added.
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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