Separation techniques

Separation Techniques

These separation techniques can be used to seperate mixtures, since mixtures can be seperated by physical means.

Mixtures

A mixture contains more than one substance. The substances are just mixed together, and not chemically combined. For example: air is a mixture nitrogen, oxygen, and small amounts of other gases

Simple distillation

This is a way to obtain the solvent from a solution. It could be used to obtain water from salt water, for example. Like this:

Distillation

  • Heat the solution in the flask. As it boils, water vapour rises into the condenser, leaving salt behind.
  • The condenser is cold, so the vapour condenses to water in it.
  • The water drips into the beaker. It is called distilled water. It is almost pure.

The liquid that is collected after passing through the condenser is called the distillate.

Fractional distillation

If miscible liquids are to be separated, then this can be done by fractional distillation. Fractional distillation relies upon the liquids having different boiling points.This is used to separate a mixture of liquids from each other.You could use it to separate a mixture of ethanol and water, for example.

QUESTION

A mixture contains aqueous sodium chloride and insoluble powdered charcoal (carbon).

(i) Suggest how the powdered charcoal can be separated from the mixture. ….[1]
(ii) Suggest how water can be removed from aqueous sodium chloride. …[1]

    SOLUTION

  1. By filtration
  2. By distillation

Fractional distillation in industry

In fractional distillation, the liquids collected are called fractions

Chromatography

Chromatograhy is used to separate two or more substances that have different solubilities. This technic is used when you have to seprate mixtures of coloured materials such as inks and dyes. There are several types of chromatography; however, they all follow the same basic principles. The simplest kind is paper chromatography. To separate the different coloured dyes in a sample of black ink, a spot of the ink is put on to a piece of chromatography paper. This paper is then set in a suitable solvent.

As the solvent moves up the paper, the dyes are carried with it and begin to separate. They separate because the substances have different solubilities in the solvent and are absorbed to different degrees by the chromatography paper.The most soluble one travels fastest. As a result, they are separated gradually as the solvent moves up the paper

Chromatography

QUESTIONS

  1. How would you obtain pure water from seawater? Draw the apparatus, and explain how the method works.

Distillation

The method is called distillation. Setup the apparatus as shown in the diagram above. Heat the flask containing the seawater until the water evaporates. The water vapour will pass through the condenser where it is cooled and condensed back to liquid. Collect the pure water in a clean flask.