The substances in a mixture are not chemically joined, so a mixture can be separated by physical methods. Filtration separates an insoluble solid from a liquid, such as sand from water. The mixture is poured through filter paper in a funnel. The solid stays on the paper as the residue, and the liquid that passes through is the filtrate.
Crystallisation obtains a soluble solid from its solution. The solution is heated gently to evaporate some of the solvent until it is saturated, then left to cool slowly so that crystals form. The crystals are filtered off, washed with a little cold distilled water and left to dry.
Simple distillation separates a solvent from a solution, such as water from salt solution. The solution is heated, the water boils and the vapour passes into a condenser. There it cools and condenses to a liquid, which is collected as the distillate. The salt is left behind in the flask.
Fractional distillation separates liquids that mix together (miscible liquids) and have different boiling points. Ethanol boils at 78 °C and water boils at 100 °C. When the mixture is heated, the vapour rises up a fractionating column. The liquid with the lower boiling point, ethanol, reaches the top first, passes through the condenser and is collected first. The water, with the higher boiling point, stays in the flask or condenses and drips back down the column.
