Higher and foundation tiers

Purity and formulations

In everyday language there are many words which are commonly used which have a different meaning in science. One such word is "pure". You may see adverts for pure orange juice or pure milk. In science a pure substance is one which contains only a single element or compound. Milk and orange juice are mixtures and are not pure substances. Milk for example contains a mixture of water, fat, proteins, sugars, vitamins and minerals and so it is not a pure substance but a mixture of many substances. In this case where for example the label on a bottle of orange juice describes it as pure it is referring to the fact it is in its natural state and has had nothing added to it.

A pure substance made up of only one element or compound will have a sharp melting and boiling point. For example water boils at 100⁰C and melts at 0^oC, if there are impurities in the water then it is no longer just water and its melting and boiling points will no longer be 100⁰C and 0^oC. You can use the melting and boiling points of a substance to determine just how pure it is, the closer the melting and boiling points are to those in a data book for the substance then the purer the sample you have will be.

Formulations

Formulations are mixtures of substances specifically designed for a certain purpose. Paint is a formulation; it contains:

• A pigment to give it the desired colour.
• Binder to hold the particles of pigment together in paint when it dries.
• A solvent to help the binder and pigment spread easily and evenly when painting.

• Fuels such as petrol and diesel as well as specialised fuels for racing cars and planes.
• Cleaning fluids have many uses; whether it is window cleaners, floor cleaning fluids, surface cleaners, they will have different mixtures of substances or formulations to give the desired properties.

More formulations

A look at the composition label will tell you the amounts of each ingredient in the mixture or formulation. Other formulations include medicines, fertilisers, alloys and foods. Baby milk powders are available with many different formulas where each formula or formulation is designed to meet the needs of the baby at a particular stage in its development.

Key Points

• In chemistry a pure substance is a single substance not mixed with anything else.
• Pure substances melt and boil at one specific temperature. Mixtures will melt over a temperature range as each substance in the mixture may melt at different temperatures
• Formulations are mixtures that are designed for a specific purpose. The components in a formulation will be mixed in carefully measured amounts to ensure the product has the desired properties.
• Formulations include: foods, medicines, paints, alloys, cleaning agents and fertilisers.

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