AP Chemistry Helpppppp!!!?

Question

Please Help:

Which if the following is lower for a 1.0-molar aqueous solution of any solute than it is for pure water?

A) pH
B)Vapor pressure
C)Freezing point
D)Eliectrical conductivity
E)Absorption of visible light

Answer 1

Letter C

Answer 2

If we consider "any solute", then we can refute the following:

Solute = NaOH, pH is higher than 7, so A is out.

Vapor pressure is not an issue, so B is out.

Solute = NaCl, conductivity is higher than pure water, so D is out. (Actually, water doesn't conduct electricity, it's the contaminants that do. Pure water is 18 mho)

Many solutes will absorb visible light (look at food colorings), so E is out.

C is the answer, and it makes sense. In an aqueous solution, the freezing point depresses because of the inability to form the nice crystaline structure needed for ice. (The important thing here is it's an aqueous solution - if it was a suspension of fatty acids, this wouldn't be true - fatty acids could raise the FP, as it will begin to order the water molecules.)

Answer 3

pH depends on whether you have an acid, base or neutral solution so it can't be the answer.

vapor pressure depends on the evaporation of the water which does not depend on what is dissolved in the water so it can't be the answer.

we know freezing point is lowered by the addition of solutes, so C is a correct answer.

electrical conductivity depends on the conductivity of the solute;; it could be a strong electrolyte, a weak electrolyte or a nonelectrolyte so D can't be the answer

absorption of visible light depends on whether or not the solute forms a solution with color so E can not be the answer.