Why does salt make ice colder? Salt needs to use energy to be dissolved into water. The salt actually uses the energy from the water. When salt takes the energy from water, it changes not only the melting point but also its boiling point. When you add salt to ice, it lowers its melting point making it colder. When you add salt to water that you plan to heat, the salt raises the boiling point.
I am no scientist so you would probably be better off reading a physical chemistry book to get the correct scientific answer.