Question

The action of heat on the blue crystalline solid X gives a reddish brown gas Y, a gas which re-lights a glowing splint and leaves a black residue. When gas Z, which has a rotten egg smell, is passed through a solution of X, a black ppt. is formed.

1. Identify X, Y and Z.
2. Write the equation for action of heat on X.
3. Write the equation between solution X and gas Z.

Answer 1

1. X is copper nitrate \[\ce{[Cu(NO3)2]}\], 

Y is nitrogen dioxide \[\ce{[NO2]}\] and

Z is hydrogen sulphide \[\ce{H2S}\]

2. \[\ce{\underset{Blue crystalline}{2Cu(NO3)2} ->[heat] \underset{Black}{2CuO} + 4NO2 + O2}\]

3. When a \[\ce{H2S}\] gas, which has a rotten egg smell, is passed through a solution of \[\ce{Cu(NO3)2}\], a black ppt. of CuS is formed.

\[\ce{Cu(NO3)2 + H2S ->CuS + 2HNO3}\]