Freezing-point depression

Examples include adding salt into water (used in ice cream makers and for de-icing roads), alcohol in water, ethylene or propylene glycol in water (used in antifreeze in cars), adding copper to molten silver (used to make solder that flows at a lower temperature than the silver pieces being joined), or the mixing of two solids such as impurities into a finely powdered drug.

In a similar manner, the chemical potential of the vapor above the solution is lower than that above a pure solvent, which results in boiling-point elevation.

Melting point determinations are commonly exploited in organic chemistry to aid in identifying substances and to ascertain their purity.

Road salting takes advantage of this effect to lower the freezing point of the ice it is placed on.

[5] In other animals, such as the spring peeper frog (Pseudacris crucifer), the molality is increased temporarily as a reaction to cold temperatures.

Cryoscopy is no longer as common a measurement method as it once was, but it was included in textbooks at the turn of the 20th century.

As an example, it was still taught as a useful analytic procedure in Cohen's Practical Organic Chemistry of 1910,[8] in which the molar mass of naphthalene is determined using a Beckmann freezing apparatus.

Freezing-point depression can also be used as a purity analysis tool when analyzed by differential scanning calorimetry.

In the laboratory, lauric acid may be used to investigate the molar mass of an unknown substance via the freezing-point depression.

The choice of lauric acid is convenient because the melting point of the pure compound is relatively high (43.8 °C).

[9][citation needed] This is also the same principle acting in the melting-point depression observed when the melting point of an impure solid mixture is measured with a melting-point apparatus since melting and freezing points both refer to the liquid-solid phase transition (albeit in different directions).