Mixtures and separating techniques · GCSE Chemistry

Mixtures

A mixture has two or more elements or compounds that are not chemically combined. Each substance keeps its own chemical properties.
Mixtures can be separated by physical processes, which do not make new substances.

Filtration separates an insoluble solid from a liquid, for example sand from water. The solid (residue) stays in the filter paper; the liquid (filtrate) passes through.
Crystallisation gets a soluble solid from a solution. Heat the solution in an evaporating basin to evaporate some water, leave it to cool so crystals form, then filter and dry the crystals.
Heating to dryness can be used instead, but some salts decompose when heated strongly, so crystallisation is often better.

Simple distillation separates a liquid from a solution, for example pure water from salt water. The liquid evaporates, then the vapour cools and condenses in a condenser and is collected.
Fractional distillation separates a mixture of liquids with different boiling points, such as ethanol and water, or the fractions in crude oil.
A fractionating column is hottest at the bottom and coolest at the top. Each liquid condenses at the height where the temperature is below its boiling point.

Paper chromatography separates substances in a mixture, such as the dyes in ink, because they move different distances up the paper with the solvent.
It can show whether a substance is pure: a pure substance gives a single spot.

Insoluble solid and liquid: filtration.
Soluble solid dissolved in a liquid: crystallisation (to keep the solid) or simple distillation (to keep the liquid).
Liquids with different boiling points: fractional distillation.
Several dissolved coloured substances: chromatography.

Mixture: Two or more substances that are not chemically combined.
Filtration: Separating an insoluble solid from a liquid using filter paper.
Residue: The solid left in the filter paper after filtration.
Filtrate: The liquid that passes through the filter paper.
Crystallisation: Forming crystals of a soluble solid by evaporating some of the solvent and cooling.
Simple distillation: Separating a liquid from a solution by evaporation and condensation.
Fractional distillation: Separating liquids with different boiling points using a fractionating column.
Condenser: Apparatus that cools a vapour so it turns back into a liquid.
Chromatography: Separating substances by how far they move through paper with a solvent.
Solvent: The liquid in which a solute dissolves.