Hi, I was taught that increasing the strength of intermolecular forces also increases the melting point of a solid. If this is true, then why does salt decrease the melting point of ice? I know that salt will dissociate into Na+ and Cl- ions and that these ions will form ion-dipole interactions with water. Moreover, ion-dipole interactions are stronger than hydrogen bonding so should this not increase the melting point of ice?
Freezing-point depression - Wikipedia
It’s an entropy effect:
“The explanation for the freezing point depression is then simply that as solvent molecules leave the liquid and join the solid, they leave behind a smaller volume of liquid in which the solute particles can roam. The resulting reduced entropy of the solute particles thus is independent of their properties. This approximation ceases to hold when the concentration becomes large enough for solute-solute interactions to become important.”