JAMB Chemistry 2012 Paper

Concept:Convert the volatile methanoic acid into a non-volatile salt, then separate pure water by distillation.Explanation:Sand is already insoluble, but methanoic acid dissolves in water and can evaporate with it, so simple filtration or distillation alone will not give pure water.Add $\mathrm{NaOH}$ to neutralise methanoic acid:$$\mathrm{HCOOH + NaOH \rightarrow HCOONa + H_2O}$$The product, $\mathrm{HCOONa}$, is a non-volatile salt.Distilling the mixture now leaves sand and the salt behind, while pure water distils over and is collected.Answer:B. neutralization with NaOH followed by distillation