Methods of purification

When a mixture of substances are present in a mixture it might be necessary to separate these substances in the mixture. The most suitable method has to be selected to carryout this purification. There are several purification techniques we use in chemistry.

•  Filtration and Crystallization
•  Using a suitable solvent
• Distillation
• Fractional distillation 

Filtration and Crystallization

If the mixture consists of a soluble substance and an insoluble substance this method can be used. E.g: if a mixture of salt and sand is present this mixture can be dissolved in water by which only salt is dissolved in water. sand can be separated by by filtration (how ever if the pure sample of the insoluble substance is needed it can be washed and dried). Salt dissolved in water can be obtained by crystallization. 

for filtration funnel and a filter paper is required

As shown in the diagram solution has to be poured through a funnel lined with a filter paper with a use of a glass rod

For crystallization can be done by  pouring the solution into an evaporating dish and let it evaporate. however this evaporation can be done by letting the solution dry slowly or heated by a water bath but never heated  directly  as the solution can evaporate with the solid itself. 

In selecting the method of crystallization what we have to keep in mind is 

"Slow cooling makes bigger crystals and fast cooling makes small crystals"

Using a suitable solvent

 Suppose if one substance in the mixture dissolves in water and other substance dissolves in alcohol that is when we should use this method. After dissolving the substances a separation funnel can be used to separate the substances.

Distillation

To separate a substance from a liquid mixture and if they have a considerable difference in  there boiling points this method can be used. for example to separate a mixture of ethanol and water.Ethanol is having a lesser boiling point than water so if we heat the mixture ethanol will boil first and evaporate. At that time if the vapor can be condensed by cooling the liquid can be collected.

note: the direction of the water flow for an efficient condensing process and the position
of the thermometer.

Fractional distillation

A mixture made with not only two but with many liquids and if they have a difference in their boiling points this method can be used. A fractional distillation column  is used for the process.

Arunigd 10:09 PM   distillation   filtration   fractional distillation   methods of purification   using a solvent

Author : Arunigd

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