Copper nitrate is a blue coloured crystal.
When copper nitrate is heated it loses the water molecule and then when is further heated it decomposes to give reddish brown gas, nitrogen dioxide and oxygen.
Cu(NO3)2.3H2O --heat--> Cu(NO3)2 + 3H2O
2Cu(NO3)2 --heat--> 2CuO + 4NO2 + O2
