International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What method would you use to obtain pure water from salt water?

1. Simple distillation

2. Dissolving

3. Crystallisation

4. Filtration

The correct answer is: Simple distillation

The method used to obtain pure water from salt water is simple distillation. This process takes advantage of the different boiling points of water and salt. During simple distillation, salt water is heated, causing the water to evaporate while the salt remains in the solution. The water vapor is then cooled and condensed back into liquid form, resulting in pure water separated from the salt. Simple distillation is particularly effective for this process because it allows for the collection of water without the impurities, which in this case is the salt dissolved in the water. It is important to note that methods like crystallization would not be effective for separating pure water from salt water since crystallization involves forming solid crystals from solutions and is better suited for purifying soluble solids rather than separating them from liquids. Similarly, dissolving and filtration would not yield pure water, as dissolving does not remove the salt, and filtration would not separate dissolved salts from the solution effectively.