chemistry
posted by Joshua on .
I need to know if I have th right molecular formula for Sorbito
39.56g C
7.75g H
52.7g O
Empirical Formula is CH2O
30.026 amu
how I how calculate the molecular mass and how I figure out the melecular formula? please help

Do you mean sorbitol?
If all the information that you have is the elemental compositions then you can only calculate the empirical formula. CH2O is NOT the correct empirical formula for sorbitol.
C H O
39.56% 7.75% 52.7%
39.56g 7.75g 52.7g
3.30mol 7.75 mol 3.29 mol
1 mol 2.34 mol 1 mol
which is not CH2O
C3H7O3 is the closest
In order to calculate the molecular formula you meed the molecular mass calculated by another means. 
In other posts of this same compound, the rest of the problem was to calculate the molar mass of sorbitol from freezing point depression data. As Dr Russ notes, that information will provide the molar mass and from that you can determine the molecular formula.

so the molecular formula will be?
c= 3.30/3.29=1, H=7.75/3.29=2, O=3.29/3.29=1
2(C3H7O3)= C6H17O6
Delta T= Kf * m
T= 1.86 C/m * 0.33m/g
T= o.613 C
am i correct? 
I don't remember the numbers for the freezing point depression part of the problem, but the molar mass works out to be about 182 or so; therefore, the multiplier you have of 2 is correct. You made a typo in multiplying; however, since 2(C3H7O3) = C6H14O6 (not the H17 you typed in).

sorry it was a typo and yes they didn't ask for the freezing point thanks so much