Purity and formulation

• A pure substance is either a single element, or compound, that is not mixed with any other substance.
• A mixture consists of two or more elements/compounds, that are not chemically combined together and can be separated by physical processes.
• Pure substances will melt and boil at specific temperatures, so we can use the temperature that a substance melts/boils at to tell how pure it is. Impure substances will melt/freeze or boil/condense over a range of temperatures. 

  
• A formulation is a mixture that has been designed as a useful product.
• Many products are complex mixtures in which each chemical has a particular purpose.
• Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
• Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
• It is important that formulations keep the same ingredients, so that the formulation is always produced the same way. People buy these products for continuity, especially paints - it would be pointless buying the same shade of paint that was actually different colours.