If you had left your copper(II) nitrate/potassium hydroxide precipitate stand for a while, the precipitate would turn into a black powder. The copper doesn’t reduce in this reaction, but one mole of water is produced from the reaction of one mole of the copper precipitate. Predict the product of this decomposition reaction.

Answer 1

The ppt is Cu(OH)2.
So Cu(OH)2 ==> black? + H2O
Since the problem tells you there is no oxidation/reduction, just take out the water and see what's left. And you should know CuO is black.
Cu(OH)2 ==> CuO)(black) + H2O