CAIE A Level Chemistry 9701 · Chemistry of transition elements
An aqueous solution of cobalt(II) chloride is pink. When concentrated hydrochloric acid is added, the solution turns blue. The pink colour is due to the octahedral complex and the blue colour is due to the tetrahedral complex .
Describe, in terms of the d orbitals of the cobalt(II) ion, why the change in colour occurs.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
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