2018 O Level Chem P1 Q22 — Acids and Bases / Properties of Acids and Bases Solution

Answer: A. The correct row needs both a true statement and a correct explanation of it.

A: ammonia can be made by warming an ammonium salt with an alkali, and the explanation that the hydroxide ion acts as a base and removes \(\text{H}^{+}\) from the ammonium ion (\(\text{NH}_4^{+} + \text{OH}^{-} \rightarrow \text{NH}_3 + \text{H}_2\text{O}\)) is also correct.

B is wrong in its explanation: more ionisation gives more \(\text{H}^{+}\) and so a lower pH, not a higher one. C is wrong: metal hydroxides are alkaline, not acidic. D is wrong: when an acid reacts with a metal the metal is oxidised, not reduced. Only A is correct in both parts. Answer A.