In chemistry, a pure substance is a single element or compound — not mixed with anything else. A pure substance has a sharp, specific melting point. An impure substance (a mixture) melts over a range of temperatures and at a lower temperature than the pure substance.
A formulation is a mixture that has been designed as a useful product. Each component is carefully measured to ensure the product has the required properties (e.g. medicines, fuels, paints, pesticides, foods, and detergents).
Mixtures can be separated by physical methods because no chemical bonds need to be broken:
Filtration — separates insoluble solids from liquids
Evaporation/crystallisation — separates dissolved solids from solutions
Simple distillation — separates a solvent from a solution
Fractional distillation — separates a mixture of liquids with different boiling points
Chromatography — separates dissolved substances based on their solubility