Separation of mixture

           In the nature matter seldom occurs as pure substances, rather they occur as mixtures. Mixture can be separated into individuals components by different processes. Methods of separation depend upon the physical properties of individual components of mixture. Some commonly used laboratory processes for separation of mixtures of substances are described here. 

    

Evaporation:

 
                   

 If a little salt is added to the water and shaken well, the salt will dissolve and a homogeneous mixture of salt and water will be formed which is known as solution. The salt cannot be separated from he solution by filtration; both water and salt passed straight through the filter paper. To obtain the salt , the solution must be heated so that the water escape out as vapour leaving behind the salt. For this the solution is taken in the procelain basin and graduallyt heated to dryness over a Bunsen flame.

Filtration:

                     Filtration is the process of separating an insoluble solid substance from liquid by passsing through filter.Suppose we have turbid water. From this clear water can be obtained by filtration. For this a circular filter paper is folded twice and then opened to form a cone. This is then fitted into the  funnel. 

Pour turbid water to the filter paper in the funnel. Water penetrates through the pores of the filter paper and is collected in the beaker whgich is known as filtrate. Suspended particles remain in the filter paper which is known as residue. By this process any insoluble substance existing as suspension can be separated from the liquid. In municipal supply of water suspended particles in water are removed by filtering water through a layer of sand and gravel in a filter bed. The dust particles from air can be separated by filtering through the filter pad.

Distillation:

                     In the separation of salt from solution by evaporation the solvent water escapes out to the atmosphere. If the solvent is to be recovered, distillation should be used.Distillation is the process in which liquid is comverted to vapour by heating and the vapour is condensed back to liquid by cooling. Distillation is used for the purificxation of liquid as well as separation of two miscible liquids. For this, liquid to be distilled is taken in thedistiullation flask fitted with Leibug's condenser.

On heating, the liquids get vapourized and passes through the inner tube of 
condenser.In the outer jacket cold water  is circulated so that the vapour condenses back to the liquid which is collected in the receiver.This liquid is known as distillate. Distillated water for lead acid accumulator as well as for injection is produced by distillation.The distillation is in practice from cennturies for the preparation of spirit from the fermented wine.Two miscible liquids can also be separated from each  other if their boiling points are quite different. For better separation of liquid mixture fractional distillation  with fractioniating column should be used. Petrol , kerosene, diesel, mobil are obtained byfractional distillation of crude oilextracted from the mines.Alchemists had used a special types of glass apparatus for distillation propose which is known as retort.


 Sublimation:

                        
                      If we heat the shining iodine crystal, it will not meilt but it gives violet vapour and if this vapour is cooled it will convert back to iodine crystal. This process is known as sublimation.
Sublimation is the process of converting solid to vapor by heating and condensing vapour back to solid by cooling. Sublimation is used for the purification of substance which sublimes. This process can be used for separation of two substances in which one sublimes and the other does not. For Sublimation, the mixture is taken in a procelain basin  and a funnel is inverted over and gently heated by keeping it over a sand bath. The inverted funeel is cooled by putting a wet filter paper. The volatile solid will sublime into the funnel and is knwon as sublimate.For practice in the laboratory , amixture of sand and camphor can be separated by Sublimation process.


Crystallization:

                         For the purification of impure solid substances ,Crystallization is frequently used.
This process is most often used for the purification of crude organic compounds prepared in the laboratory. Pure crystals of copper sulphate  may be prepared from bazaar copper sulphate by Crystallization.


  


For this a saturated solution of bazaar copper sulphate is prepared and filtered. The filtrate is taken in the procelain basin and evaporated to the Crystallization point. Then this hot solution is cooled whereby pure crystals of copper sulphate separate out.