CC2.1 — Pure substances and formulations (Edexcel 1SC0)

Pure substances

A pure substance in chemistry contains only one type of element or compound — it has a sharp, definite melting point.

An impure substance melts over a range of temperatures (melting point is depressed).

Mixtures

A mixture contains two or more substances that are not chemically combined. Components retain their individual properties and can be separated by physical methods.

Formulations

A formulation is a mixture that has been carefully designed so that its components are present in the correct proportions to achieve the required properties.

Examples:

• Medicines: active ingredient + binders, fillers, coatings.
• Alloys: specific proportions of metals for desired properties.
• Fuels: blended to meet performance/environmental standards.
• Paints: pigment + binder + solvent in precise ratio.
• Foods: additives, preservatives, flavourings in correct amounts.

Chromatography for purity

Paper chromatography can separate components of a mixture. If a substance gives a single spot, it is likely pure (or all components have same Rf).