Question

How do you separate a mixture containing one water-soluble and one water-insoluble substance providing that the water insoluble particles are so small that it goes through the mesh of the filter along with the soluble?

Answer 1

The best method to separate mixture containing water soluble and water insoluble substance is using filtration using filter paper. You need to dissolve the mixture containing both in water, the water soluble part will get dissolved. So this part will get passed through this filter paper. The water insoluble part remains on the filter paper. Hence you have both parts separated.

But as you are saying water insoluble part can pass through mesh size of filter paper, so other option is,

USING TWO SOLVENTS (including water)) AND SEPARATNG FUNNEL:

• Water is a polar solvent so it dissolves the polar compound as per the concept of “like dissolve like”. So it is highly possible that your water insoluble part of the mixture will get dissolve in non-polar solvent.

Dissolve the mixture in water and non-polar solvent like hexane, ether or dichloromethane. Put this solution into separating funnel. Shake it well (placing stopper on mouth of funnel) and keep it for 2-3 minutes. You will see two separate layers (organic layer and water layer). Organic layer will have your water insoluble part and water layer will have water soluble part. Just collect the two layers separately now and evaporates the solvents. You have both of your substances separate now.

• Suppose if your water insoluble part of mixture is not soluble in non-polar solvent. Use dichloromethane as solvent, because it is denser than water hence will remain at bottom in separating funnel. As your water soluble part will be in above layer, due to gravity water insoluble part will go to dichloromethane layer. Hence you can separate easily by collecting both layers separately.