Solution: Crystalisation

Crystalisation is the process in which solute particles collide with other solid solute particles present in a solution and separate out of the solution. This process involves the formation of crystals from a supersaturated solution.

Supersaturated Solution:
- A supersaturated solution contains more solute particles than it can normally hold at a given temperature and pressure.
- Supersaturation can be achieved by dissolving a solute in a solvent at a high temperature and then slowly cooling the solution.

Process of Crystalisation:
1. Supersaturation: The solution is initially heated to dissolve a large amount of solute. As the solution cools, it becomes supersaturated and contains more solute than it can normally hold at that temperature.

2. Nucleation: The supersaturated solution is unstable and tends to crystallize. However, the process of crystal growth requires the presence of foreign particles, called nuclei, to initiate the formation of crystals. These nuclei can be provided by adding a small crystal of the solute or by scratching the surface of the container.

3. Crystal Growth: Once the nuclei are present, solute particles in the supersaturated solution collide with the nuclei and start to crystallize. The solute particles attach to the nuclei and form crystal lattice structures. This process continues as more and more solute particles collide with the growing crystals, causing them to grow in size.

4. Separation: As the crystals continue to grow, they become large enough to settle at the bottom of the container or attach to the sides of the container. This separation of the crystals from the solution is known as crystalisation. The separated crystals can then be collected and dried to obtain the pure solute.

Applications of Crystalisation:
- Crystalisation is widely used in various industries for the purification of substances. For example, in the pharmaceutical industry, crystalisation is used to purify drugs and separate them from impurities.
- It is also used in the production of table salt, sugar, and other crystalline substances.
- Crystalisation is an important technique in the field of chemistry and research for the separation and purification of different compounds.