chem question?

Question

why does a sodium chloride solution boil at a higher temp than that of water. they have equal volumes

Answer 1

I'll just quote a person who asked this question to a scientist at the Department of Energy.

"A given mass of water will not heat more rapidly if you dissolve some salt in it. If anything, it will heat more slowly, because you must heat the salt as well as the water.
The water boils at a higher temperature because the salt cannot boil with it (the boiling point of sodium chloride is very, very high). Hence in order for the water to boil the salt must come out of solution: it must undissolve. You know that dissolving is a favored process, since it always occurs instantly when you mix salt and water.

If dissolving is favored, then undissolving must be unfavored -- you never observe salt and water suddenly undissolving by themselves. Therefore extra energy (as heat) must be supplied to the salt/water solution in order to boil it, because extra energy is needed to undissolve the salt. I should say, extra energy *per atom or molecule*, which is the same thing as a higher temperature."

Answer 2

Salt or any impurity will raise the boiling point of a solvent because it interferes with the colligative properties of the solvent. This is expressed by the equation: delta T (change in boiling point temp)= Van Hoff's factor x ebullioscopic constant x molality of the solute.