Koligativní

Koligativní refers to properties of solutions that depend solely on the ratio of the number of solute particles to the number of solvent molecules in a solution, rather than on the type of solute or solvent. These properties are a direct consequence of the presence of solute particles altering the behavior of solvent molecules. The four principal colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

Vapor pressure lowering occurs because solute particles occupy some of the surface area of the liquid, reducing the rate at which solvent molecules can escape into the gas phase. Consequently, the vapor pressure of the solution is lower than that of the pure solvent. Boiling point elevation is a result of vapor pressure lowering; a higher temperature is required to reach a vapor pressure equal to the external pressure. Freezing point depression arises because the solute particles interfere with the formation of the ordered crystal lattice of the solvent. Osmotic pressure is the pressure that needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane. These properties are often used to determine the molar mass of an unknown solute.