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A mixture consists of two or more elements or compounds not chemically combined.

Crude oil is a mixture of compounds.

Most of the compounds in crude oil are hydrocarbons. Most of these are saturated (alkanes) which have the formula. CnH2n+2.

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The hydrocarbons in crude oil can be separated into fractions, each of which contains molecules with a similar number of carbon atoms. By evaporating the oil and allowing it to condense at a number of temperatures. This process is fractional distillation.

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Fuels contain carbon and/or hydrogen and may also contain some sulphur. The gases released into the atmosphere when fuels burn may include: carbon dioxide, water(vapour) carbon monoxide, sulphur dioxide, and oxides of nitrogen.Solid particles (particulates) may also be released.

The combustion of hydrocarbon fuels release energy. During combustion the carbon and the hydrogen become oxidised.

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Sulphur dioxide and oxides of nitrogen cause acid rain, carbon dioxide causes global warming, particulates cause global dimming.

Sulphur dioxide can be removed from fuels before they are burned.

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Hydrocarbons can be cracked to produce more useful molecules. This process involves heating the hydrocarbons to vaporise them, the vapours are either passed over a hot catalyst or mixed with steam and heated to a high temperature.

Alkenes have the formula CnH2n.

Double bonds are shown by =

Alkenes react with bromine water to turn it colourless.

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Plastics bags are being made from polymers and cornstarch so that they break down more easily.(BIODEGRADABLE)

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