Solution and solubility

Solution is defined as a homogeneous mixture of two or more chemical substances. The state of matter of a solution may be solid, liquid or gaseous.

For example, common salt in water (liquid solution), air (gaseous solution), alloys (solid solution), etc.

The components of a solution may be classified as:

• Solute

• Solvent

Difference between solute and solvent

Thus, an intimate mixture of solute and solvent is called a solution.

Aqueous solutions and non-aqueous solutions

Aqueous solutions

Solutions that contain water as the solvent are called aqueous solutions.

For example, sugar in water, carbon dioxide in water, etc.

Non-aqueous solutions

Solutions that contain a solvent other than water are called non-aqueous solutions. Ether, benzene, petrol, carbon tetrachloride etc., are some common solvents.

For example, sulphur in carbon disulphide, naphthalene in benzene, etc.

Concentrated solutions and dilute solutions

Between two solutions, the solute quantity may be relatively more or less. The solution that has a greater proportion of solute is said to be more concentrated than the other that has a lesser proportion. If the proportion of solute is less, the solution is said to be dilute.

Saturated and unsaturated solutions

Saturated Solution

A solution in which no more solute can be dissolved at a given temperature is called a saturated solution.

Unsaturated solution

A solution in which more solute can be dissolved at a given temperature is called an unsaturated solution.

A given solution that is saturated at a particular temperature may become unsaturated when the temperature is increased.

Solubility of a solute

Solubility is defined as the number of grams of a solute that dissolves in 100g of a solvent to form a saturated solution at a given temperature and pressure.

Solubility is the maximum weight of a solute that can be dissolved in 100g of a solvent at a given temperature and pressure.

Factors affecting the solubility of a solid solute in water

Temperature

Increase in temperature increases the solubility.

For example, it is easier to dissolve sugar in hot milk than in cold milk.

Size of solute particles

Smaller the size of the particles greater is the solubility.

For example, it is easier to dissolve powdered sugar than granules of sugar.

Mechanical stirring

Mechanical stirring increases solubility.

For example, sugar dissolves faster on stirring with a spoon.

Factors affecting the solubility of a gas in water

Temperature

Increase in temperature, decreases the solubility of a solute. On heating, the gases dissolved in milk escape making the milk bubble and boil over.

Pressure

An increase in pressure increases the solubility of a gas.

For example, aerated water bottles contain carbon dioxide gas under pressure.