Distillation
Learn more on distillation and chromatography in this podcast.
Listen to the full series on 大象传媒 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 pure water from seawater.
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. leaves the solution. It moves away and is cooled and A change of state in which gas becomes liquid by cooling.. The remaining solution becomes more concentrated as the amount of solvent in it decreases.
Image caption, Simple distillation
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 different liquids from a mixture of liquids. It is useful for separating The alcohol which is produced as a result of fermentation of sugars by yeast. from a mixture of ethanol and water, and for separating 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. from crude oil.
Fractional distillation works because the different liquids have different boiling points. When the mixture is heated:
- vapours rise through a column which is hot at the bottom, and cooler at the top
- vapours condense when they reach a part of the column that is below the temperature of their boiling point
- each liquid is led away from 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
- by continuing to heat the mixture to increase the temperatures in the column - the substance with the lowest boiling point is collected first
Image caption, Distillation process to separate ethanol from water
1. Water and ethanol solution is heated
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