How does salt affect the boiling point of water?

Question

And if it lowers/highers the boiling point, why?

Answer 1

Salt raises the boiling point of water and lowers its freezing point. Therefore if you took two pots of the same amount of water (one with salt and the other pure) and added heat to them at the same rate, the salt water would take longer to reach a boil since it would need to be raised to a higher temperature than the pure water before it began to boil.

WHY:
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.

Answer 2

Damon_p is right...don't listen to anybody telling you that salt lowers the boiling point! The truth is that any solute (dissolved solid) will lower the freezing point and RAISE the boiling point.

The reason is simple, also described by Damon_p. If you add a solute to a liquid, you reduce the chances that a random molecule will be able to escape the liquid, thereby reducing the 'vapor pressure' (number of liquid particles at any given moment that have become a gas).

Now, if you have a sample of water that wants to boil, by adding salt, you've decreased its ability to send particles into the air. Since the water's going to have to expend more energy to get all those particles into the air, it's going to take longer for it to boil. The boiling point goes up!

I must amend one fact, though--not enough salt is added to pasta water to significantly change its boiling point. According to wikipedia (I just found this out, too), this is just to keep the pasta from sticking.

Answer 3

Salt lowers the boiling point of water. Adding salt to water to be boiled can make cooking a little faster!

Answer 4

Yes, it does affect the boiling point. Adding salt (NaCl) into water increases the boiling point. This is because of the presence of impurities. If a substance has a lower vapour pressure than the liquid (it’s relatively non-volatile in other words) then dissolving that substance in the liquid, common salt (NaCl) in water (H2O), for instance, will lower the overall vapour pressure of the resulting solution compared with the pure liquid. A lower vapour pressure means that the solution has to be heated more than the pure liquid to make its molecules vaporise. It is an effect of the dilution of the solvent in the presence of a solute.

Answer 5

Listen to the chem teacher he, and some others are correct. Salt or for that matter any solute added to water will have the same affect, to raise the bp, and lower the freezing point of water. This is the same reason antifreeze in your car radiator prevents it from freezing in the winter and prevents boiling over in the summer.

Answer 6

Salt highers the boiling point of water, when your cooking you add salt to the water to make it hotter, thus reducing the cooking time. The salt dissolves in the water and absorbs some of the heat applied to it, so the total temperature goes up. Adding salt also reduces the freezing point of water by getting in the way of crystal formation. thats why we salt roads in winter.

Answer 7

It raises the boiling temperature, lowers the freezing temperature, and lowers vapor pressure. These are called colligative properties. The extent of the effect is determined by the number of particles not the chemical identity of the particles that you dissolve in the liquid; with more particles the boiling temperature is elevated more, the freezing temperature is lowered more and the vapor pressure is lowered more.

Answer 8

adding a salt to water will increase the boiling point of water according to the following equation:
Delta T = Kb * (m2/M2) * (1000/m1)
where:
Delta T= the increase in boiling point
Kb= a constant (specific for that salt)
m2= wight of the salt in grams
M2= Molecular wight of the salt
m1= weight of the water in grams
The reason is: the dissolved salt is ionic in solution and it adds new electrostatic attractions between water molecules which make it more difficult for them to escape from solution

Answer 9

OH DEAR who deosnt know O level chemistry!

salt (any salt in fact) LOWERS tthe FREEZING point of water by displacing the crystalisation matrix causing voids that need more energy to fill (it needs to be colder)..

SALT RAISES the boiling point of water by interferring with the surface tension as water molecules are more strongly attracted to salt ions than water so need more energy to be released eg it has to be hotter to boil

Answer 10

Adding salt increases the molality and raises the boiling point.