In the last column, we had looked at chemical reactions. Under the same conditions, some substances will react, some will just change state, some may remain unchanged. To study reactions, we have to be sure that the chemicals we are studying are pure, as we need to know that the reactions are because of a particular substance, and not because of anything else in the mixture. There are standard methods of separation, some used in everyday life, some specialized. To demonstrate the various methods, let’s consider the kind of mixtures that can be present:
|Type of mixture||Method of separation||Examples|
|solid/solid||any difference in properties like solubility, magnetic behaviour,||sea salt*, iron and aluminium, copper sulfate commercial grade*|
|solid/liquid insoluble||muddy water, petrol and salt||filteration|
|solid/liquid soluble||sea water*, sugar solution||distillation, fractional crystallization, chromatography*|
|liquid/liquid immiscible||oil and water,* petrol and water||using a separating funnel|
|liquid/ liquid miscible||alcohol and water, crude oil, felt pens*||fractional distillation, gas chromatography#|
# very specialized technique
* will be discussed
Sea water is an interesting mixture, it has many salts dissolved in it and will usually contain some sand, i.e., it is an example of both soluble and insoluble solid/liquid mixtures. You can make your own sea water by dissolving sea salt (available in the market) in water. About 7g in 200 cm3 will make an acceptable replacement to sea water. The solution will be cloudy because of the sand and mud in the sea salt. Filteration will give a clear solution, containing many salts. These can be separated by fractional crystallization.
The author works with Centre for Learning, Bengaluru. She can be reached at firstname.lastname@example.org.