Question on: SS1 Chemistry - Solutions and Concentration

Solutions are homogeneous mixtures consisting of a solvent (the substance that dissolves other substances) and solute (the substance being dissolved). The concentration of solute in a solution determines its saturation level, leading to three types of solutions: saturated, unsaturated, and supersaturated.

 

Saturated Solutions:

A saturated solution is one in which the maximum amount of solute has been dissolved at a given temperature and pressure. In a saturated solution, any additional solute added will not dissolve and will instead settle at the bottom. The concentration of the solute in a saturated solution remains constant, as the rate of dissolution equals the rate of precipitation. Saturation depends on factors such as temperature and the nature of the solute and solvent.

 

Unsaturated Solutions:

An unsaturated solution is one that has not reached its maximum solute concentration and can still dissolve more solute at a given temperature and pressure. In an unsaturated solution, the amount of solute present is less than the maximum solubility of that solute in the solvent. As a result, the concentration of the solute can vary, and additional solute can dissolve. Unsaturated solutions can become saturated by adding more solute or by evaporating the solvent to increase the concentration.

 

Supersaturated Solutions:

A supersaturated solution is formed when a solvent holds more solute than it normally can at a particular temperature and pressure. This is achieved by dissolving a solute at a higher temperature and then rapidly cooling the solution without allowing the excess solute to precipitate. Supersaturated solutions are highly unstable and can spontaneously return to a saturated state by the slightest disturbance or seeding with a crystal of the solute. These solutions are characterised by having a solute concentration higher than the equilibrium solubility.