WAEC Chemistry 2016 Paper

Concept:Ammonium sulfate is a salt formed from a strong acid and a weak base, so its aqueous solution is acidic due to hydrolysis.Explanation:$(\mathrm{NH}_4)_2\mathrm{SO}_4$ is the salt of sulfuric acid ($\mathrm{H}_2\mathrm{SO}_4$), a strong acid, and ammonia ($\mathrm{NH}_3$), a weak base.When dissolved in water, the ammonium ion ($\mathrm{NH}_4^+$) undergoes hydrolysis to produce hydrogen ions.The relevant equation is:$\mathrm{NH}_4^+ + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{NH}_3 + \mathrm{H}_3\mathrm{O}^+$The production of $\mathrm{H}_3\mathrm{O}^+$ makes the solution acidic.Sulfate ion ($\mathrm{SO}_4^{2-}$) comes from a strong acid, so it does not hydrolyse to affect the pH.Answer:A. Acidic