system
Given the following post, respond as if you're commenting on Reddit:
human
If salt raises the boiling temp of water, is there additive that will let water freeze at a higher temp also?
gpt
Adding salt depresses the freezing point of water - that’s why municipalities salt the roads in the winter where it is snowy and icy.

Both the boiling point elevation and freezing point depression are types of colligative properties (in case you want to read more - use that term).

Colligative properties are about how the properties of a solvent (in this case water) can be changed by an added solute. It doesn’t matter what the identity of the solute is, it only matters how many particles are present (the particles essentially get in the way of the interactions between the water molecules).

Fundamentally what occurs is that you lower the vapor pressure curve of the solution relative to the pure solvent. This causes both the boiling point elevation and the freezing point depression. So there is no way to add a substance to water and increase its freezing point, because the solvent is still water.