Separating solids from liquids – filtration

If a substance does not dissolve in a solvent, we say that it is insoluble. For example, sand does not dissolve in water – it is insoluble.

Filtration is a method for separating an insoluble solid from a liquid. When a mixture of sand and water is filtered:

• the sand stays behind in the filter paper (it becomes the residue)
• the water passes through the filter paper (it becomes the filtrate)

The slideshow shows how filtration works:

A beaker containing a mixture of insoluble solid and liquid. There is filter paper in a filter funnel above another beaker.

The mixture of insoluble solid and liquid is poured into the filter funnel.

The liquid particles are small enough to pass through the filter paper as a filtrate. The solid particles are too large to pass through the filter paper and stay behind as a residue.