Question

Ammonia gas is passed over heated copper (II) oxide in a combustion tube:

1. Name the gas evolved.
2. What will be the colour of the residue that is left in the combustion tube at the end of the reaction?

Answer 1

1. The gas evolved is nitrogen.
   \[\ce{2NH3 + 3CuO -> 3Cu + 3H2O + N2}\]
2. The residual colour in the combustion tube at the end of the reaction will be reddish brown due to the reduction of black copper oxide to reddish brown copper by ammonia.