Freezing-point Depression

Freezing-point depression describes the process in which adding a solute to a solvent (i.e. salt in water, alcohol in water), or the mixing of two solids (such as impurities in a finely powdered drug) (in such cases, the added compound is the solute, and the original solid can be thought of as the solvent) produces a decrease in the freezing point of the solvent. The resulting solution or solid-solid mixture has a lower freezing point than the pure solvent or solid did. This phenomenon is what causes sea water, (a mixture of salt (and other things) in water) to remain liquid at temperatures below 0 °C (32 °F), the freezing point of pure water.