How exactly does salt raise the boiling point (and lower the freezing point) of water?

these are the so called colligative properties. in a molecular basis, the salt is breaking the hydrogen bond network of the water molecules, and the counterions associate with the water's dipoles. this interaction requires a higher energy to evaporate, and colder temp to freeze.

hope this helps.

Adding salt to water raises the temperature that the water boils at. The more salt you add, the higher the temperature. Adding 2 tablespoons of salt to 2 cups (473 milliliters) of water can raise the boiling point from 212 degrees Fahrenheit (100 degrees Celsius) by 5 degrees to 217° F (102.8° C). [Corel] Sea salt When water is about to boil, the water molecules near the surface bop around. Many get kicked by nearby jiggling molecules and the extra energy careens them into the air. Of course, many air molecules right above also move around. Some of these air molecules collide with the escaping water molecules and knock them back into the water. Water boils when enough individual surface molecules have enough energy to zap past air molecules directly above the water surface. Suppose we add salt to the water that's about ready to boil. Now the surface has both salt molecules and jiggling water molecules. So, a water molecule has a smaller chance of getting kicked by a neighbor hard enough to escape because some neighbors are lethargic salt molecules. So, fewer water molecules at the surface get past the air molecules. The water won't boil until the temperature is higher and the water molecules on the surface are bopping around faster.

adding impurites increase the boiling point and decrease the melting point.water will require a higher temperature to evaporate.

Thay's why roads are sprayed with salt in winter to lower the melting point of ice and snow and cause it to melt while the temperature is actually lower that its melting point.

the range of boiling-freezing points of things are directly proportional to density.that's why when you add salt to water it raises the density hence increasing the boiling-freezing point range.>>>>got it!!!