Colligative Properties – Class 12 | Chapter – 2 | Chemistry Short Notes Series PDF for NEET & JEE
Colligative Properties: Colligative properties are properties of solutions that depend only on the number of solute particles in the solution, not on the identity of the solute particles. In other words, colligative properties are properties that are affected by the concentration of the solute, but not by the chemical nature of the solute.
Types of Colligative Properties
There are four main colligative properties:
- Vapour pressure lowering: The presence of a non-volatile solute in a solvent reduces the vapour pressure of the solvent. This is because the solute particles occupy some of the surface area of the solvent, making it more difficult for the solvent molecules to escape into the vapour phase.
- Boiling point elevation: The presence of a non-volatile solute in a solvent increases the boiling point of the solvent. This is because the higher the concentration of the solute in the solution, the more energy is required to vaporize the solvent.
- Freezing point depression: The presence of a non-volatile solute in a solvent lowers the freezing point of the solvent. This is because the solute particles disrupt the formation of the solvent’s crystal lattice structure, making it more difficult for the solvent to freeze.
- Osmotic pressure: When a semi-permeable membrane separates two solutions of different concentrations, the solvent will tend to flow from the region of lower concentration to the region of higher concentration. This flow of solvent generates an osmotic pressure, which is proportional to the difference in concentration between the two solutions.
Importance of Colligative Properties
Colligative properties are important for several reasons, including:
- Molecular weight determination: Colligative properties can be used to determine the molecular weight of unknown compounds. By measuring the change in vapour pressure, boiling point, or freezing point caused by the addition of a known amount of solute to a solvent, it is possible to calculate the molecular weight of the solute.
- Preservation of food and other perishable materials: Colligative properties are important in the preservation of food and other perishable materials. By adding solutes such as salt or sugar to food, the freezing point is lowered, which can prevent the formation of ice crystals that can damage the texture and flavour of the food.
- Industrial applications: Colligative properties are also important in industrial applications, such as the production of chemicals, fuels, and other materials. By controlling the colligative properties of solutions, it is possible to design processes that can separate and purify compounds, or produce desired products from raw materials.
- Biological processes: Colligative properties are also important in biological processes, such as the regulation of water balance in cells. The osmotic pressure generated by the difference in solute concentration across a cell membrane is essential for the maintenance of cell structure and function.
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