Many of the useful materials we use every day are mixtures. A formulation is a mixture that has been designed as a useful product. It is made by mixing several components in carefully measured amounts, and each component has a purpose. The amounts are chosen so that the product has the required properties. Fuels, cleaning products, paints, medicines, fertilisers and many foods are formulations.
An alloy is a mixture of a metal with at least one other element, which is often another metal. Alloys are mixtures, not compounds, because the substances are not chemically joined in fixed proportions. Brass is an alloy of copper and zinc, and steel is an alloy of iron with a small amount of carbon.
Pure metals are usually soft because their atoms are in layers that can slide over each other easily. In an alloy the atoms of the added element are a different size from the atoms of the main metal. They distort the regular layers, so the layers cannot slide easily. This makes an alloy harder than the pure metal. Making an alloy is a way of designing a metal with the properties needed for a job.
