Question

(a)
(i) Write the balanced chemical equation to prepare ammonia gas in the laboratory by using an alkali.
(ii) State why concentrated sulphuric acid is not used for drying ammonia gas.
(iii) Why is ammonia gas not collected over water?
[3]

(b)
(i) Name the acid used for the preparation of hydrogen chloride gas in the laboratory. Why is this particular acid preferred to other acids?
(ii) Write the balanced chemical equation for the laboratory preparation of hydrogen chloride gas.
[3]

(c) For the preparation of hydrochloric acid in the laboratory:
(i) Why is direct absorption of hydrogen chloride gas in water not feasible?
(ii) What arrangement is done to dissolve hydrogen chloride gas in water?
[2]

(d) For the electro-refining of copper:
(i) What is the cathode made up of?
(ii) Write the reaction that takes place at the anode.
[2]

Answer 1

(a)
(i) $2N{H}_{4}Cl+Ca{\left(OH\right)}_2\stackrel{\Delta }{\to }CaC{l}_2+2H_{2}O+2N{H}_3$
(ii) Concentrated sulphuric acid reacts with ammonia / form ammonium sulphate or $N{H}_3$ being basic combines with concentrated $H_{2}S{O}_4$/correct chemical equation.
(iii) $N{H}_3$ is highly soluble in water or dissolves in water.

(b)
(i) Concentrate sulphuric acid. It is nonvolatile / has high boiling point / displaces the volatile hydrogen chloride from the salt sodium chloride.
(ii) $NaCl+H_{2}S{O}_4(conc.)\underset{}{\overset{<200\circ C}{\to }}NaHS{O}_4+HCl$
(c)
(i) Back suction occurs (or the description of back suction) / HCl gas dissolves in water at a faster rate than it is produced.
(ii) Inverted funnel arrangement/ the rim of the funnel just touches the surface of water taken in the trough or correct diagram.

(d)
(i) Pure copper
(ii) $Cu-2e^{-1}\to C{u}^{+2}/Cu\to C{u}^{+2}+2e^{-1}$