JERRY MASON / SCIENCE PHOTO LIBRARY JERRY MASON / SCIENCE PHOTO LIBRARY
Reaction between copper(II) sulphate and ammonium hydroxide. In the test tube at left is a solution of copper(II) sulphate. When a small amount of ammonium hydroxide is added (centre) a precipitate of copper(II) hydroxide is formed. Adding more ammonium hydroxide dissolves the copper(II) hydroxide (right). This is thermodynamically unstable with respect to dehydration, so quickly forms copper(II) oxide. This is also soluble in ammonium hydroxide, so not precipitate forms, but a deep blue colour is seen in solution.
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