Evaporation
When a solid dissolves in a liquid (like salt in water), we cannot use filtration or sedimentation because the particles are too small and mixed thoroughly.
To separate them, we heat the mixture.
Definition: The process in which a liquid gets converted into its vapour is called evaporation.
The Process
- Heat the solution containing the dissolved solid.
- The water (solvent) boils and turns into steam (vapour).
- The solid (solute) cannot evaporate, so it is left behind in the container.
Real-World Example: Making Salt
Common salt (namak) is obtained from seawater.
- Seawater is trapped in shallow pits (lagoons).
- It is exposed to sunlight and wind.
- The water slowly evaporates over a few days.
- Solid salt crystals are left behind.
- This crude salt is then purified for consumption.
Tip
Activity Reflection: If you mix salt in water, filter it (salt passes through), and then boil it dry, you will see white residue in the vessel. That is the salt you recovered!