Question

(a) What is the action of red litmus on
(i) dry ammonia gas (ii) solution of ammonia gas in water?

(b) State the observations you would make on adding ammonium hydroxide to aqueous solution of
(i) Ferrous sulphate (ii) Aluminium chloride. [3 MARKS]

Answer 1

Each point: 1.5 Mark

1. (i) Red litmus has no action on dry ammonia gas, because it does not release any hydroxyl ions.

(ii) When passed through water, ammonia ${\text{NH}}_3$ is converted to ammonium hydroxide ${\text{NH}}_4\text{OH}$. It dissociates to give hydroxyl ions ${\text{OH}}^{-}$ and the solution is basic in nature. Red litmus acquires a blue colour.

2. (i) A green precipitate of ferrous hydroxide will be formed by double decomposition reaction.

${\text{FeSO}}_4\text{(aq)}+2{\text{NH}}_4\text{OH}\text{(aq)}\to {\text{Fe(OH)}}_2+{\text{(NH}}_4{)}_2{\text{SO}}_4\text{(aq)}$

(ii) A white precipitate of aluminium hydroxide will be formed by double decomposition reaction.

${\text{AlCl}}_3\text{(aq)}+3{\text{NH}}_4\text{OH}\text{(aq)}\to {\text{Al(OH)}}_3+3{\text{NH}}_4\text{Cl}\text{(aq)}$