[maakii]

Any one knows why we have to add tartaric acid to a solution of Fe²⁺/Fe³⁺and neutralize it with ammonia before adding any KCN?

I'm guessing it has something to do with the pH change involved after adding KCN, since CN^- would hydrolyse water (correct me if i'm wrong =x), so a buffer solution is needed, but this seems a bit farfetched..hope someone knows the answer