Methods of Separating Mixtures (IV)

EVAPORATION

Evaporation is used to separate dissolved solutes. Two liquids cannot be separated through filtration because both liquids will pass through the filter paper and nothing will be separated. When a solute (solid) dissolves in a solvent (liquid), evaporation can be used to separate it.

Separation using evaporation is when the solution is heated and the solvent evaporate leaving the solute (solid) behind. This method is usually done to obtain common salt.

Both filtration and evaporation can be used to separate two solids. An example for such mixture is salt and sand. This mixture can be separated through filtration and evaporation.

The experiment is performed below:

Activity: Separating Salt and Sand.

Materials: Salt, sand, water, filter paper stirrer, source of heat (Bunsen burner), evaporating basin.

Method:

1. Put about 15g of salt and sand into about 100cm3 of water.
2. Stir the mixture well.
   (a) What happens to the mixture?
   (b) Record your observation
3. Filter the mixture carefully and collect the filtrate (solvent) in an evaporating basin.
   (c) What is observed on the filter paper?
   (d) Examine the filtrate carefully, did you notice some solid particles in it? Record your observations.
4. Heat the evaporated basin to allow the water to evaporate off.
5. Turn off the bunsen burner after all the water has evaporated.
   (e) Taste a little of what remains in the basin and record your observations.

Diagram

NB: In salt and sand preparation, the method of filtration is performed first before evaporation.