IGCSE Chemistry Topic 2: Purity

Pure Substance

Single element or a single compound that has a specific melting point and boiling point because it contains only one type of particle

Impure Substance

An impure substance is a mixture of two or more elements or compounds that has a range of boiling and melting point temperatures

Filtration

a mechanical or physical separation process that separates solid particles from liquids or gases by passing the mixture through a filter

Crystallization

Seperating the soluble solid by evaporating the solvent, and allowing it to cool to form crystals

Paper Chromatography

Seperating dissolved chemical substances by taking analysing their different rates of migration across sheets of paper.

Distillation

Boiling the solution and then condensing the vapour back into a liquid by cooling it down

RF Value

Distance moved by the substance divided by the distance moved by the solvent front

How do you interpret chromatography results for purity?

A pure substance produces one spot on a chromatogram, while an impure substance produces multiple spots, and unknown substances can be identified by comparing spot positions and Rf values to known samples.

How do you choose the right separation method?

You choose based on the mixture's properties: filtration for solid-liquid, crystallization for soluble solids, simple distillation for liquids from solutions, and fractional distillation for multiple liquids.