Concept:Methanoic acid and water have nearly the same boiling point, so the acid must first be converted into a non-volatile salt before distilling out pure water.
Explanation:Sand is insoluble and non-volatile, so it will not interfere with distillation.
Methanoic acid is neutralized by sodium hydroxide to form sodium methanoate, which is an ionic salt:
HCOOH+NaOH→HCOONa+H2OThis salt remains in the distillation flask together with sand because it is not volatile.
When the mixture is heated, only water boils over and is collected as pure distillate.
Ordinary distillation cannot be used before this neutralization because water and methanoic acid have close boiling points.
Filtration alone cannot remove dissolved methanoic acid or sodium methanoate, so a final distillation step is necessary.
Answer:C. Neutralization with sodium hydroxide followed by distillation