Which of the following methods can be used to obtain pure water from a mixture of sand, water and methanoic acid?

Correct answer: Filtration followed by distillation.

Why: Sand is an insoluble solid, so remove it first by filtration. The remaining mixture is water + methanoic (formic) acid, which are miscible. Use simple distillation to boil and condense the water, collecting it as pure distillate while the acid largely remains in the flask.

• Neutralization with NaOH followed by filtration – Incorrect. Neutralization produces sodium formate (a dissolved salt). Filtration will not remove dissolved salts, so the water would not be pure.
• Neutralization with NaOH followed by distillation – Not the best method. Although distillation could still yield water, you have unnecessarily added a reagent and created a salt solution; a physical separation (filter → distill) is preferred.
• Fractional distillation – Unnecessary and it ignores the sand. You would still need to filter first, and simple distillation is sufficient after filtration.
• Filtration followed by distillation – Correct. Filter out sand, then distill to obtain pure water.