Question

state your observation when ammonia gas is passed over black copper oxide

Answer 1

1. When ammonia is passed over black copper oxide, black colour of CuO changes to brown colour of Cu and slowly ammoniacal smell fades away.

2. This is because of the following redox reaction:

3 CuO + 2 NH₃ $\to$ N₂ + 3 H₂O + 3 Cu

3. In this, Cu is reduced from +2 to 0 oxidation state and N is oxidised from -3 to 0 oxidation state.