Chemistry: Solutions and Mixtures

Study Notes

A solution is a homogeneous mixture containing two or more components, where the component present in larger quantity is called the solvent, and the component(s) present in smaller quantity is called the solute.
Solutions can be classified into different types based on the physical state of the solute and solvent:
- Gaseous solutions: Gas in gas, liquid in gas, solid in gas
- Liquid solutions: Gas in liquid, liquid in liquid, solid in liquid
- Solid solutions: Gas in solid, liquid in solid, solid in solid

Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent at a particular temperature.
Solubility depends on the nature of the solute, nature of the solvent, temperature, and pressure.
"Like dissolves like" is a general principle of solubility, where polar solutes dissolve in polar solvents and non-polar solutes in non-polar solvents.
Saturated and unsaturated solutions:
- Saturated solution: A solution in which no more solute can be dissolved at the same temperature and pressure.
- Unsaturated solution: A solution in which more solute can be dissolved at the same temperature.

The solubility of a solid in a liquid mainly depends on temperature.
In general, if the dissolution process is endothermic, the solubility increases with rise in temperature, and if it is exothermic, the solubility decreases with rise in temperature.
Pressure does not have a significant effect on the solubility of solids in liquids.
The solubility of a gas in a liquid is greatly affected by pressure and temperature.
Henry's law states that at a constant temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas.

Vapour pressure is the pressure exerted by the vapour in equilibrium with its own liquid.
Vapour pressure depends on the nature of the liquid and the temperature.
As the temperature increases, the vapour pressure also increases.

Raoult's law states that for a solution of volatile liquids, the partial vapour pressure of each component is directly proportional to its mole fraction in the solution.
The vapour pressure of a solution is always lower than that of the pure solvent.
The decrease in vapour pressure depends on the quantity of non-volatile solute present in the solution and not on its nature.

Ideal solutions: Solutions that obey Raoult's law over the entire range of concentration.
Non-ideal solutions: Solutions that do not obey Raoult's law over the entire range of concentration.
Non-ideal solutions can be classified into two types:
- Solutions that show positive deviation from Raoult's law: Vapour pressure of the solution is higher than that predicted by Raoult's law.
- Solutions that show negative deviation from Raoult's law: Vapour pressure of the solution is lower than that predicted by Raoult's law.

Azeotropes are binary mixtures having the same composition in liquid and vapour phase and boil at a constant temperature.
Azeotropes can be classified into two types:
- Minimum boiling azeotrope: Formed by solutions that show a large positive deviation from Raoult's law.
- Maximum boiling azeotrope: Formed by solutions that show a large negative deviation from Raoult's law.