CAIE A Level Chemistry 9701 · Chemistry of transition elements
A student dissolves anhydrous cobalt(II) chloride in water, producing a pink solution. On adding concentrated hydrochloric acid, the solution turns blue. The blue species is the tetrahedral complex ion .
Suggest explanations for the colour change and for the change in coordination number.
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.
Suggest means: Apply what you know to an unfamiliar situation. There may be more than one acceptable answer. Reason from the principle you have learned to the new context, and say which principle you are using.
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