Distillation
Learn more on distillation and chromatography in this podcast.
Listen to the full series on BBC Sounds.
Simple distillation
Separation method used to separate a solvent from a solution. is used to separate a The liquid in which the solute dissolves to form a solution. from a Mixture formed by a solute and a solvent.. It is useful for producing water from salt solution.
Simple distillation works because the A substance is said to be dissolved when it breaks up and mixes completely with a solvent to produce a solution.The dissolved substance in a solution. has a much higher The temperature at which a substance rapidly changes from a liquid to a gas. than the solvent. When the solution is heated, solvent Gas formed below the boiling point of a substance.When liquid is vaporised and turns to a gas. from the solution. The vapour is cooled and Turned from a gas or vapour into a liquid, usually as a result of cooling.. The remaining solution becomes more The concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present. as the amount of solvent in it decreases.
Image caption, 1. Salty water is heated
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Fractional distillation
In fractional distillation a mixture of several substances, such as crude oil, is distilled and the evaporated components are collected as they condense at different temperatures. is used to separate the different liquids from a mixture of liquids. It works because the different liquids have different The temperature at which a substance rapidly changes from a liquid to a gas.. When the mixture is heated:
- vapours rise through a column which is hot at the bottom, and cold at the top
- vapours Condensation is a change of state in which gas becomes liquid by cooling. when they reach a part of the column that is below the temperature of their boiling point
- the liquid flows out of the column
There are two ways of obtaining different liquids from the column:
- By collecting different liquids from different parts of the column. The substance with the lowest boiling point is collected at the top of the column. Different In fractional distillation, such as that of crude oil, the different parts of the original mixture are called fractions. The substances in each fraction have similar boiling points to each other. are separated from Mixture of hydrocarbons, mainly alkanes, formed over millions of years from the remains of ancient dead marine organisms. this way.
- By continuing to heat the mixture to increase the temperatures in the column. The substance with the lowest boiling point is collected first. The alcohol which is produced as a result of fermentation of sugars by yeast. is separated from a mixture of ethanol and water this way.
Image caption, 1. Water and ethanol solution is heated
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