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Science

Fuels

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Crude oil is a fossil fuel that can be separated into many different products called fractions. When fuels burn, they react with oxygen in the air, but if there is not enough air this can lead to 'incomplete combustion' which results in the production of a toxic gas called carbon monoxide. Alternatives to fossil fuels include biofuels (eg vegetable oils) and hydrogen.

Distillation

Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points. Distillation is commonly used to separate ethanol - the alcohol in alcoholic drinks - from water.

Distillation process to separate ethanol from water

water and ethanol solution are heated in a flask over a bunsen burner, pure vapour is produced in the air above the solution within the flask.

Step 1 - water and ethanol solution are heated

The mixture is heated in a flask. Ethanol has a lower boiling point than water so it evaporates first. The ethanol vapour is then cooled and condensed inside the condenser to form a pure liquid. The thermometer shows the boiling point of the pure ethanol liquid. When all the ethanol has evaporated from the solution, the temperature rises and the water evaporates.

This is the sequence of events in distillation:

heating → evaporating → cooling → condensing

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