How do i solve this problem?

Question

EMERGENCY!!!! Please help as soon as possible.


Elemental analysis indicates the simplest formula of an unknown is C2H4O. When 0.775 gm of the compound is dissolved in 50gm of Benzene (C6H6), the solution freezes at 5.06˚C. What are the molecular weight and molecular formula of the compound? The freezing point of pure Benzene is 5.48˚C, and its Ksubf is 5.12˚C/m.

Answer 1

From the freezing point depression you can compute the number of moles of C2H4O in the solution. (You must find out if your Ksubf is for molar or molal concentration. Hopefully it is for molal concentration, since you were given the mass of the solvent, not the volume.) The molal concentration of C2H4O is then M = ∆T/Ksubf = (5.48-5.06)/5.12 = 0.082 moles/kg. You have 50gm (0.05kg) of solution, so the 0.775gm represents 0.082*0.05 = 0.0041 moles. One mole is then 0.775/0.0041= 189 gm. That (189) is the molecular mass of the compound. Add up the atomic masses of 2*C, H, and 4*O to see how many molecules it takes to make up that mass.

NOTE: If the Ksubf is for molar concentration, you get an approximate value by converting the 50gm of benzene to volume by dividing by the density of benzene.

Answer 2

Molecular formula is C8H16O4 Molecular Weight is 176.

Answer 3

I don't know! Really !