| Complexation Reaction
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When a small amount of aqueous ammonia is added to copper(II) sulfate, a pale blue copper(II) hydroxide precipitate forms. Addition of excess aqueous ammonia breaks up the precipitate and forms a bright blue tetraaminecopper(II) complex ion. This is an example of a complexation reaction. Adding more copper(II) sulfate causes a precipitate of copper(II) hydroxide precipitate to reform.