Question

Define evaporation. How is it used for separating mixtures?

Answer 1

Hint: Evaporation means vaporisation from the surface of liquid. Condensation is the reverse process of evaporation. Both evaporation and condensation processes are in equilibrium with each other.

Complete answer:
-Evaporation is the process by which liquids can be converted into gaseous form with the help of heat. -Heat is being absorbed during such a process.
-Heat energy is necessary for evaporation to occur. When evaporation occurs there is a reduction in the temperature of the liquid which results in cooling.
-Evaporation of water occurs when the surface of liquid is exposed allowing molecules to escape and form water vapours then the vapours rise up and form clouds.
-For the molecules of liquid to evaporate they must be located near the surface, they must have sufficient kinetic energy to overcome the forces present in the solution. At high temperature the molecules have higher kinetic energy so the rate of movement is also high. Hence evaporation increases. The factors that play an important role in the evaporation are heat and atmospheric pressure. Temperature is also one of the major factors affecting the rate of evaporation.
-Evaporation can be used for separating homogeneous mixtures having solid dissolved in liquid. This requires heat. Once the liquid is completely evaporated only solid is left behind.
-Salt is obtained from the evaporation of seawater. The heat for the process comes from the sun.
-Evaporation can also occur at temperatures below boiling point of a liquid. Boiling point is the temperature at which vapour pressure of liquid becomes equal to atmospheric pressure.

Note:Homogenous mixtures are the mixtures in which solute and solvent are in the same phase. -Heterogeneous mixtures are the mixtures wherein the solute and solvent are in different phases.
-Evaporation method is only used for separating homogeneous mixtures when solid is dissolved completely in liquid. It is not useful for separating heterogeneous mixtures. They can be separated out by filtration.