Copper oxide test:
1. The organic substance is mixed with three times its weight of dry copper oxide by grinding. The mixture is placed in a hard glass test rube fitted with a bent delivery tube. The other end of which is dipping into lime water in an another test tube. The mixture is heated strongly.
2. 2CuO + C → CO2 + 2Cu
CuO + 2H → H2O + Cu
3. Thus if carbon is present, it is oxidized to CO2 which turns lime water milky. If hydrogen is also present, it will be oxidized to water and condenses in small droplets on the cooler wall of the test tube and inside the bulb. Water is collected on white anhydrous CuSO4 which turns blue.
4. This confirms the presence of C and H in the compound.