Chemistry

Matter in Our Surroundings

To Separate the Salt-Water Mixture (or Salt-Solution)

A mixture of common salt and water can be separated completely by the process of distillation. The apparatus used for distillation is shown in Figure 78.
The salt and water mixture is taken in the distillation flask A and heated (see Figure 78.). On heating,water forms vapours (steam) which rise up and come out through the side tube B of the distillation flask,and go into water condenser C. Cold water from the tap is circulated through the outer tube of condenser for cooling the vapours. The hot water vapours get cooled in the condenser to form pure water which trickles down from the condenser and collects in the beaker D. This pure water is called distilled water.Since the salt is non-volatile (it does not form vapours on heating), so it remains behind in the distillation flask. (Some porcelain pieces are put in the distillation flask in the beginning to have uniform boiling throughout the solution and avoid bumping of the solution due to uneven heating).
From the above discussion we conclude that distillation can be used to separate a liquid from dissolved non-volatile solids. Now, ordinary tap water always contains some dissolved salts in it and is never pure.So,pure water or distilled water is made from tap water by the process of distillation. There are many coastal areas where drinking water is not available in adequate quantity. The process of distillation is used to obtain drinking water from sea-water in many countries.
Distillation can also be used to separate a mixture of two miscible liquids having different boiling points. The liquid having lower boiling point distils over first, and the liquid having higher boiling point distils later. Each liquid, however, contains some amount of the other liquid, so a complete separation of two miscible liquids cannot be done by simple distillation. For the complete separation of two (or more) miscible liquids, the process of fractional distillation is used.

Notes

Matter in Our Surroundings - Notes

1. 9. Non-Metals Have Low Densities.