Question

X, Y and Z are three crystalline solids that are soluble in water and have a common anion.

To help you to identify X, Y and Z, you are provided with the following experimental observations. Copy and complete the corresponding inferences in (a) to (e).

1. A reddish-brown gas is obtained when X, Y and Z are separately warmed with concentrated sulphuric acid and copper turning added to the mixture.
   INFERENCE 1: The common anion is the ______ ion.
2. When X is heated, it melts and gives off only one gas which re-lights a glowing splint.
   INFERENCE 2: The cation in X is either ______ or ______.
3. The action of heat on Y produces a reddish-brown gas and yellow residue which fuses with a glass of the test tube.
   INFERENCE 3: The metal ion present in Y is the ______ ion.
4. When Z is heated, it leaves no residue. Warming Z with sodium hydroxide solution liberates a gas which turns moist red litmus paper blue.
   INFERENCE 4: Z contains the ______ cation.
5. Write the equations for the following reactions:
   1. X and concentrated sulphuric acid (below 200°C). (One equation only for either of the cations given in INFERENCE 2)
   2. The action of heat on Y.
   3. Concentrated nitric acid is added to copper turnings kept in a beaker.

Answer 1

1. A reddish-brown gas is obtained when X, Y, and Z are separately warmed with concentrated sulphuric acid and copper turning added to the mixture.
   INFERENCE 1: The common anion is the nitrate ion.
2. When X is heated, it melts and gives off only one gas which re-lights a glowing splint.
   INFERENCE 2: The cation in X is either sodium or potassium.
3. The action of heat on Y produces a reddish-brown gas and yellow residue which fuses with a glass of the test tube.
   INFERENCE 3: The metal ion present in Y is the lead ion.
4. When Z is heated, it leaves no residue. Warming Z with sodium hydroxide solution liberates a gas which turns moist red litmus paper blue.
   INFERENCE 4: Z contains the ammonia cation.
5. 
   
   1. \[\ce{KNO3 + H2SO4 ->[<200^\circ C]KHSO4 + HNO3}\]
   2. \[\ce{\underset{(Colourless crystalline)}{2Pb(NO3)2} ->[\Delta] \underset{(Yellow fuses with glass)}{2PbO + 4NO2 + O2}}\]
   3. \[\ce{Cu + 4HNO3 ->Cu(NO3)2 + 2H2O + 2NO2}\]