1. Elements, Compounds and Mixtures

A pure substance made up of two or more elements chemically combined.

A combination of two or more substances (elements and/or compounds) that are not chemically combined.

• A pure substance may consist of a single element or compound which contains no other substances.

• Pure substances melt and boil at specific and sharp temperatures • Impure substances have a range of melting and boiling points as they consist of different substance

• Simple distillation separates a liquid from a soluble solid or a pure liquid from a mixture. • The solution is heated, the liquid evaporates and turns to vapour, which passes through a condenser, cools, and condenses into a pure liquid. • The solid remains behind after all the liquid has evaporated.

• Fractional distillation separates miscible liquids by their boiling points. • The mixture is heated; the liquid with the lowest boiling point evaporates first, passes through a condenser, cools, and is collected. • This leaves the other components behind.

Filtration separates an undissolved solid from a liquid. The mixture is poured into a filter funnel with filter paper. Liquid passes through as filtrate, while solid particles stay behind as residue. Wash the solid and place it in a warm oven to dry.

• Crystallisation separates a dissolved solid from a solution. • The solution is heated to evaporate some solvent, creating a saturated solution. • It is tested with a glass rod — if crystals form, it is saturated. • The solution cools slowly, forming crystals as solubility decreases. • Crystals are filtered, washed with cold distilled water, and dried.

• Paper chromatography separates substances by their solubility in a solvent. • Spots of sample are placed on a pencil line on chromatography paper, which is then placed in solvent. • The solvent rises by capillary action, carrying substances at different rates. • More soluble substances travel further, separating the mixture into its components.

• Pencil is used for this as ink would run into the chromatogram along with the samples. • The pencil line must stay above the solvent.

(Mass of solid / Mass of water removed) x 100

• Pure substances will produce only one spot on the chromatogram • Impure substances will produce more than one spot on the chromatogram

Distance moved by substance / Distance moved by solvent