Filtration
Filtration is a technique used to separate mixtures according to their solubility. Consider a mixture of salt and sand. The apparatus on the left is used to separate the sand from the salt solution. The filter paper acts as a sieve separating the particles by size. Small particles flow through the tiny holes of the filter paper while large particles become trapped.

 

When mixed with water the salt dissolves while the sand remains as a solid. We say the sand is insoluble. The salt dissolves in the water by been torn apart by the water molecules, as shown on the right. This reduces the salt crystals to their smallest building blocks.

The atomic sized building blocks of the salt can easily pass through the small holes of the filter paper while the sand particles, shown on the right, are trapped and remain in the filter paper.

Solid particles that remain in the filter paper form the residue, while the solution that passes through the filter paper is known as the filtrate.

 

1) What property of salt and sand is used to separate the salt from a mixture of salt and sand?

2) Chalk and salt are accidentally mixed together. The mixture is placed in water and stirred before been passed through filter paper. What passes through the filter paper is collected in a beaker.
a) What remains in the filter paper?

b) What passes through the filter paper.?

c) The filtrate is the

d) The residue is the

e) The residue is found in the

Recovery of salt by evaporation