What is Separation of Substances?
Many of the substances that we use every day were once a part of some or the other mixture. Separating substances from mixtures is a vital part of Chemistry and modern industry. This is done to separate the useful substances from a mixture, and also to remove non-useful or harmful components.
Methods of separation of substances
Filtration is one of the most common methods used for separating substances. Filters are used everywhere. You use them in your houses to filter impurities from the water and also to filter dust out of the air you breathe.
Distillation is a technique that uses boiling to separate components of liquid solutions. Different substances in a mixture have different boiling points, and distillation just works on that. For example, if you heat salt water in a container, the water in the solution will boil way before the salt. The water will evaporate leaving behind the salt. When the substances in a solution have similar boiling points, a more complex type of distillation called fractional distillation is used. Crude oil is separated into gasoline, jet-fuel, diesel-fuel, propane and heating oil etc.
Centrifuges are mechanical devices that revolve at very high speeds and are used to separate substances. At these high speeds, the heavier particles move to the outside of the cylinder and are separated from the mixture. This technique is used for separating blood into plasma and red cells, and also for separating cream from milk.
In Threshing process, bunches of crop plants are beaten against a hard thing like a stone or floor to separate the grains from the stalks. When the quantity of grains is small, threshing is done manually, and when it is large, it is either done with the help of animals or machines.
In this method, particles of different sizes are run through a sieve which separates them. The bigger particles are retained by the sieve while the smaller ones easily pass through it. All of you would have seen your moms running the prepared tea from the sieve before serving. It is done to separate the tea leaves from the tea.
It is the process which uses the wind to separate the lighter particles from the heavier ones. The farmers drop the mixture of wheat and husk from a height. The blowing wind carries the husk with it and the grains fall down on the ground.
In a given mixture, the insoluble and heavier particles settle down at the bottom. This process is known as sedimentation. For example, if you dissolve some sand in a glass of water, after some time it will settle down at the bottom of the glass. It happens because sand is insoluble in water and the particles are heavier. Decantation is the removal of the clear layer of the liquid on the top without disturbing the underlying settled solids.
Evaporation is the process of liquids turning into to a gas or vapor. This technique is used to separate salt from water. Sea water is collected in shallow pits and the water is allowed to evaporate in the heat of the sun. Once the water has evaporated, the salt crystals are left behind in the pit and collected.
The process of conversion of water vapor into its liquid form is known as condensation. For example, water vapor in the clouds condenses in form of rain. If you pour cold water in a glass, you will see that water droplets will form on the outer surface of the glass. This is due to the condensation of water vapor present in the atmosphere.
9. Paper Chromatography
This method is mostly used in the food industry for identifying chemicals or coloring agents in different food items. You can think of chromatography as a race; all the runners start together from the starting line but finish the race at the different times because of their different abilities. Similarly, if you drop a mixture at a paper chromatograph, different chemicals in it would travel at different speeds over the chromatograph because of their different chemical properties and get separated from one another.
Magnetism is ideal for separating mixtures in which one component has magnetic properties. Some metals like iron, nickel and cobalt have magnetic properties whiles gold, silver and aluminum do not.