X, Y and Z are three crystalline solids which 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).

(a) 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.

(b) 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 ……………

(c) The action of heat on Y produces a reddish-brown gas and a yellow residue which fuses with the glass of the test tube.

INFERENCE 3: The metal ion present in Y is the …………… ion.

(d) 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.

(e) 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. Action of heat on Y.
3. Concentrated nitric acid is added to copper turnings kept in a beaker.

(a) The common anion is the nitrate ion.

(b) The cation in X is either sodium or potassium

(c) The metal ion present in Y is the lead ion.

(d) Z contains the ammonium ion

(e) The balanced equations are:

1. Reaction between Potassium nitrate and concentrated sulphuric acid (below 200° C):

$\underset{[\text{conc.}]}{\text{KNO}$3} + \underset{[\text{conc.}]}{\text{H}2\text{SO}4} \xrightarrow{\lt 200 \degree\text{C}} \underset{[\text{acid salt}]}{\text{KHSO}4} + \text{HNO}_3

2. 2Pb(NO₃)₂ $\xrightarrow{\Delta}$ 2PbO + 4NO₂ + O₂

3. Cu + 4HNO₃ (conc.) ⟶ Cu(NO₃)₂ + 2H₂O + 2NO₂.

Explanation

(a) On adding copper to acidified nitrates and heating, dense reddish brown fumes of nitrogen dioxide [NO₂] are evolved.

(b) The alkali metal nitrates such as sodium or potassium nitrates when heated melts into colourless liquids which decompose on heating to give oxygen gas.

$2\text{KNO}$3 \xrightarrow{\Delta} 2\text{KNO}2 + \text{O}_2

$2\text{NaNO}$3 \xrightarrow{\Delta} 2\text{NaNO}2 + \text{O}_2

(c) Lead nitrate decomposes on heating to give nitrogen dioxide, oxygen gas and yellow residue of lead oxide which fuses with the glass of the test tube.

2Pb(NO₃)₂ $\xrightarrow{\Delta}$ 2PbO + 4NO₂ + O₂

(d) Ammonium nitrate decomposes explosively on heating leaving behind no residue.

NH₄NO₃ $\xrightarrow{\Delta}$ N₂O + 2H₂O

Ammonium nitrate reacts with sodium hydroxide to give sodium nitrate, ammonia, and water. Ammonia gas turns moist red litmus paper blue.

NH₄NO₃ + NaOH ⟶ NaNO₃ + NH₃ + H₂O