Methods of separation of substances under wet conditions
Some solid particles are insoluble in water. For example chalk powder, dust particles, sand, and tiny pieces of straw are insoluble in water. To separate this type of particles generally we use the following methods
Sedimentation and Decantation
The process of separating insoluble substances which are heavier than liquid by allowing them to settle down on their own due to gravity is called sedimentation. The particles which settle down during sedimentation are called sediments.
Decantation follows sedimentation. In this process the clear upper liquid is poured out from the container without disturbing the sediment. The upper clear liquid is called supernatant.
For example muddy water contains heavier particles like sand and soil. Leave this muddy water undisturbed for some time. The heavier soil and sand particles settle down. And the clear upper water is poured out from the container.
Filtration is a process by which insoluble solids can be removed from a liquid by using a filter paper.
A filter paper is a special type of paper which has pores that are tiny enough to let only liquids pass through it. If you pass a solution through filter paper, any undissolved solid particles will get left behind on the paper whereas the liquid will filter through.
The liquid that passes through is called the filtrate and the undissolved solid particles are called residue.
Example: A mixture of chalk powder and water can be separated by this method.
To separate the soluble solids form liquids we use evaporation and condensation methods.
The process of conversion of water into vapour by heating it to its boiling point is called evaporation.
The salt can be easily obtained from the salty water by the process of evaporation. If we boil this water, the water evaporated completely, leaving behind only the salt.
The process of conversion of water vapour into its liquid form is called condensation.
Example: The water vapour condenses and we receive the same water in the form of rain.
If you pour cold water in a glass, you will observe the formation of water droplets on the outer surface of the glass . This is due to the condensation of water vapour present in atmosphere.
Solution and solubility
Separation of substances using more than one method
A mixture of sand and salt can be separated by combination of methods. The first method is sedimentation and decantation. This mixture is put in water and left for the sand to settle for some time. Then, we will decant the salty water, which will separate the sand from the mixture. Now the salt can be separated from the water by evaporation. The water will boil away, leaving the salt behind. So, the mixture of the sand, salt and water has been separated successfully using a combination of sedimentation, decantation, evaporation and condensation.
A solution is prepared by dissolving a substance in a liquid.
Solute + Solvent = Solution
Salt + water = Salt solution
A solution is said to be saturated if it cannot dissolve more of the substance in it at a particular temperature.
A solution is said to be unsaturated if it can dissolve more of the substance in it at a particular temperature.