How does salt make water temperature rise when boiling?

Answer 1

Salt (or other solutes, like sugar) can easily dissolve in liquid water. However, taking the solute out of the water and putting it in the gas phase (air) requires a lot of energy. At temperatures around the water boiling point, these solutes stay in the liquid.

Now the total pressure in the liquid and the air at the boundary are the same- otherwise one would push the other into a smaller space. Part of the pressure in the liquid comes from the solutes, not the water. So the pressure due to the water alone is reduced compared to that of pure water at the same temperature. The vapor pressure, that is, the pressure of water vapor that would stay in equilibrium with the liquid, is reduced by the same amount because of the solutes.

Water boils when the vapor pressure of the water gets to be as big as the pressure of the atmosphere. At that point, vapor bubbles in the water can grow. You have to heat the liquid with solutes up more to get the vapor pressure in it to equal the atmospheric pressure, so it has a higher boiling point.

Hope this helps...

Answer 2

Some of the explanations given are OK, but not quite accurate.

Boiling occurs when the vapor pressure over a liquid equals atmospheric pressure (which is why water boils at lower temperatures at higher elevations). The exchange between vapor phase and liquid phase can only take place at the surface of the liquid. In pure water, all of the molecules at the surface are water molecules; when you add salt, some of the molecules at the surface are either sodium ions or chloride ions, so the exchange process at the same temperature will not produce the same number of molecules per unit area (which is pressure), thus the water will not boil. It will take more energy to force water molecules to evaporate to make the vapor pressure = atmospheric pressure. More energy = higher temperatures, thus the boiling point goes up.

Answer 3

Change in BP= kb(a constant for water)*molality of salt*2

The kb is the boiling point constant of water
Molality is moles of salt divided by kg solvent(water)
2=Vand't Hoff factor, which equals 2 for salt since each NaCL molecule gives two ions: Na+ and Cl-.

The why is because the salt ions reduce the partial pressure of water vapor by nudging themselves between water molecules and reducing their motion. Since boiling point is the point where water vapor has a pressure equal to atmospheric pressure, that water must be heated to a higher temperature to achieve the necessary vapor pressure.

Answer 4

Salt dissociates into Na+ and Cl- ions in aqueous solution. These ions disrupt the ability of water molecules to vaporize at 100C (at 1 atm). This raises the water's boiling point because, in this case, water molecules require more kinetic energy to break free from the liquid state.

This is an example of the colligative property "boiling point elevation".

Answer 5

distilled water (at STP) cannot be a liquid over 212 degrees farenheit. You can put water in a 500 degree oven, and the water will not get over 212 degrees. Anything dissolved in the water causes disorder, and increases the boiling point (as well as decreases the freezing point) Salt, sugar, alcohol, antifreeze, whatever. So, if you add salt to the water, you increase the boiling point, therefor the water can get hotter before it evaporates.

Answer 6

As the salt concentration increases concentraion of the solute in water increases which in turn increases the vapor pressure and increases the boiling point water.

Answer 7

it is a colligative property..the 4 kinds of colligative properties are
1) Vapor Pressure
2) Osmotic Pressure
3) Freezing Point Depression
4) Boiling Point Elevation--this is what the salt does. It increases the boiling point of the solvent (water), allowing it to boil faster and cook quicker.

Answer 8

Boiling point elevation occurs because the sodium and chloride ions make it more difficult for the water molecules to break out into gas phase.