Quick questions on Methods of purification and separation: N(A)-Level Chemistry

Filtration separates an insoluble solid from a liquid. Pour the mixture through filter paper in a funnel. The solid is trapped as the residue; the liquid that passes through is the filtrate. This works because the solid particles are too big to pass through the tiny holes in the paper.

Simple distillation separates a liquid (the solvent) from a dissolved solid, and collects the pure liquid. The solution is heated, the liquid boils and turns to vapour, the vapour passes into a condenser where it cools back to liquid, and the pure liquid drips into a flask. It is used to get pure water from salt water.

Fractional distillation separates two or more liquids that mix together but have different boiling points, such as ethanol and water, or the liquids in crude oil. A fractionating column above the flask gives a tall surface where vapour condenses and re-evaporates many times. The liquid with the lowest boiling point reaches the top and comes off first; the others follow as the temperature rises.

Paper chromatography separates a mixture of dissolved coloured substances, such as the dyes in an ink. A spot of the mixture is placed on paper and a solvent soaks up through it. Substances that dissolve well and are weakly held by the paper travel further, so the components spread into separate spots.

Name the method used to obtain pure water from a solution of sugar in water. [1 mark]

A student wants to recover dissolved copper(II) sulfate crystals from its solution without the crystals breaking down. State the best method and why. [2 marks]

Black ink is spotted on chromatography paper and separates into three coloured spots. Explain what this tells you about the ink. [2 marks]