What are the main applications of solution freezing point reduction?

1. In winter, it is often necessary to add proper amount of ethylene glycol or methanol to the cooling water of automobile radiator to prevent freezing.

2. The freezing temperature of ice salt bath is much lower than that of ice bath, and these applications are based on the principle of freezing point reduction.

3. In snowy winter, pine leaves are evergreen but not frozen, because a lot of sugar has been stored in the leaves before winter, which greatly reduces the freezing point of leaf liquid.

In organic chemistry experiments, the method of measuring boiling point or melting point is often used to test the purity of compounds. This is because the compound containing impurities can be regarded as a solution, the compound itself is a solvent, and impurities are solutes, so the substance containing impurities has a lower melting point than the pure compound and a higher boiling point than the pure compound.

Factors of freezing point (melting point) change

pressure

The melting point of a substance (freezing point, the same below) usually refers to the situation at one atmospheric pressure; If the pressure changes, the melting point will also change. There are two different situations in which the melting point changes with pressure. For most substances, the melting process is a process of increasing volume. When the pressure increases, the melting point of these substances will increase. For substances like water, unlike most substances, the volume of ice melting into water will decrease (metals such as bismuth and antimony will also decrease), and the melting point of ice will also decrease when the pressure increases.

Dissolved impurity

If a small amount of other substances or impurities are dissolved in the liquid, even if the amount is small, the melting point (freezing point, the same below) of the substance will change greatly. For example, when salt is dissolved in water, the melting point (the temperature at which solid and liquid exist and are in equilibrium) will drop significantly. Seawater is water with dissolved salt, and the freezing temperature of seawater is lower than that of river water in winter, which is the reason. The melting point of saturated brine can be reduced to about -22℃.