WAEC Chemistry 2012 Paper

Concept:Ammonium salts release ammonia gas when reacted with a strong base.Explanation:Ammonium nitrate, $\mathrm{NH_4NO_3}$, is an ammonium salt.When a base such as sodium hydroxide reacts with it, double displacement occurs.The reaction is:$$\mathrm{NH_4NO_3(aq) + NaOH(aq) \rightarrow NaNO_3(aq) + NH_3(g) + H_2O(l)}$$Ammonia gas, $\mathrm{NH_3}$, is given off.This happens because the hydroxide ion from the base reacts with the ammonium ion.Among the options, only $\mathrm{NaOH}$ is a strong metal hydroxide (base).Acids like HCl and $\mathrm{CH_3COOH}$ would not produce ammonia.$\mathrm{CaSO_4}$ is a salt and does not provide hydroxide ions.Answer:B. $\mathrm{NaOH}$