CAIE A Level Chemistry 9701 · Chemistry of transition elements
Aqueous cobalt(II) ions exist as the pink complex . When concentrated hydrochloric acid is added, the solution turns blue as the complex forms. Explain this colour change in terms of d-orbital splitting and the effect of ligands.
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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