Methods of Separation - Evaporation Method

Evaporation: Evaporation is a process which is used to separate a solid substance dissolved in liquid. It is based on the fact that liquids vaporize easily whereas solids do not.

Evaporation Method:

Evaporation is a process which is used to separate a solid substance dissolved in liquid. It is based on the fact that liquids vaporize easily whereas solids do not.

Application:

1. Separation of salt from seawater

2. Crude petroleum refinery

Experiment to obtain coloured component (dye) from blue /black ink.

The blue ink (or black ink) used; in fountain pens is a liquid mixture. It is a mixture of a dye in water. This dye is the colored component of the ink (which gives it a blue or black color). We can separate the colored component of ink (or dye from ink) by the process of evaporation.

Aim: To separate the colored component from the ink.

Requirements: Beaker, watch-glass, water, ink, burner, etc

Principle: The volatile substance will be evaporated due to the low boiling point and the non-volatile substance will remain.

Procedure:

• Fill half a beaker with water.
• Put a watch glass on the mouth of the beaker.
• Put few drops of ink on the watch glass.
• Now start heating the beaker. We do not want to heat the ink directly as it is decomposed by the high temperature, so we use a water bath for evaporating ink. You will see that evaporation is taking place from the watch glass.
• Continue heating as the evaporation goes on and stop heating when you do
  not see any further change on the watch glass.

Observation: 

1. Water evaporates from the watch glass. This is because on heating water changes into its vapour state. The ink does not evaporate or sublime.
2. There is a residue on the glass in form of a bluish or violet color. This is ink that has precipitated and settled at the bottom of the watch glass.
3. Ink is not a single substance and not pure. Ink is a mixture and is formed by mixing water with a dye.  

Result/Inference: The non-volatile matter was separated from the volatile matter because of the difference in the boiling point.