Question

What is meant by evaporation to dryness?

Answer 1

Hint: Water is an important solvent as it can dissolve many compounds. Chemical compounds that were dissolved in water can be separated by two methods namely crystallization and evaporation to dryness. In evaporation of dryness the compound that was dissolved in water or any other compound can be heated to remove all the water molecules which leads to the formation of solid particles.

Complete Step By Step Answer:
So many inorganic salts can exist as hydrated salt which means the salt combines with the water molecule. In and hydrated salts, the water molecules will be removed.
Evaporation of dryness is the technique that can drive off all the water molecules, and forms a hydrated salt.
For example, copper sulphate exists as hydrated salt with the molecular formula of $ CuSO_4.5H_2O $ , this hydrated copper sulphate is generally in blue colour. When this salt is evaporated to dryness, the copper sulphate becomes hydrated and changes from blue colour to colourless.
Evaporation to dryness results in driving of all the water molecules, resulting in the formation of a hydrated salt which will be a powder-like substance.
Evaporation to dryness is more useful to separate the solutes that are thermally stable.

Note:
Evaporation to dryness simply means a strong heating to drive all the water molecules from the compound. Some solutions like sugar solution cannot be separated by evaporation to dryness as the sugar turns into caramel. As the sugar on strong heating loses water molecules and turns into a brown coloured substance known as caramel.