An aqueous solution containin 1 g of sorbitol in 100g water has a freezing point of 0.102 C. Elemental analysis indicates that sorbitol is 39.56% C, 7.75% H, and 52.7% O. What are the molar mass and the molecular formula of sorbitol? The Kf of water is 1.86 C/m.
Two problems in one here.
First, determine the molar mass from the freezing point. I'm sure you have made a typo; I think the freezing point should be -0.102 C and not +0.102 C.
Use delta T = Kf*molality
Calculate molality.
Then knowing that the definition of molality is #mols/kg solvent, calculate molar mass. I found approximately 180 but you need to do the work to get it exactly.
Second part of the problem. Take 100 g sample. This will give you
39.56 g C.
7.75 g H.
52.7 g O.
Change grams of C,H, and O to mols.
Then find the ratio of each element to each other with the smallest number being 1; then convert that to a set of small whole numbers. You should end up with
CxHyOz. You are determining x,y, and z. That will give you the empirical formula.
Third step.
Divide the molar mass you found in the first part of the problem by the mass for the empirical formula and that will tell you the number of empirical units there are in the formula which will give you the molecular formula.
Post your work if you get stuck.