A little bit of Chemistry..

Hey guys. No idea whether I'll be able to get some help with this.. but let's just say i'm skipping the problem for now.

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Elemental analysis of an unknown pure substance indicates that the percent composition by mass is as follows:

Carbon - 49.02%

Hydrogen - 2.743%

Chlorine - 48.23%

A solution that is prepared by dissolving 3.150 grams of the substance in 25.00 grams of benzene, C6H6, has a freezing point of 1.12°C. (The normal freezing point of benzene is 5.50°C and the molal freezing-point depression constant, Kf, for benzene is 5.12 C°/molal.)

(a) Determine the empirical formula of the unknown substance.

(b) Using the data gathered from the freezing point depression method, calculate the molar mass of the unknown substance.

(c) Calculate the mole fraction of benzene in the solution described above.

(d) The vapor pressure of pure benzene at 35°C is 150. millimeters of Hg. Calculate the vapor pressure of benzene over the solution described above at 35°C

I would greatly appreciate any help. I have the empirical formula one and If I could just figure out 2, I'd be good as far as (c) goes!
I think that most of it is just due to the fact that I have no idea which formulas to do.

 

Given is the mass composition of that substance:

Carbon - 49.02%

Hydrogen - 2.743%

Chlorine - 48.23%

Have you tried converting that to moles?

 

The empirical formula question is simple. It's b) and d) I don't understand.