A compound of carbon, hydrogen, and oxygen was burned in oxygen, and 2.00g of the compound produced 2.868 g CO2 and 1.567 g H2O. In another experiment, 0.1107 g of the compound was dissolved in 25.0 g of water. This solution had a freezing point of -0.0894 degrees C. what is the molecular formula of the compound?

Question

DrBob222 · Answer

Convert g CO2 to g C. 2.868 x (atomic mass C/molar mass CO2 = ?
Convert g H2O to H. 1.567 x (2*atomic mass H/molar mass H2O) = ?

2.00 - gC - gH = g O.
Convert g to mols.
mols = grams/atomic mass

Find the ratio of the elements to each other. This will give you the empirical formula. I came up with C3H8O3 BUT that doesn't make sense considering the molar mass. Check your post for accuracy, especially with the numbers.
You can see what I'm talking about with this.
delta T = Kf*m
Solve for m

m = mols/kg solvent.
Solve for mols.

mols = grams/molar mass
Solve for molar mass and I end up with about 26 which CAN'T possibly be right if the empirical formula is C3H8O3.

Brian · Answer

Isn't the molar mass 92.09 g/mol? This is what i got with /\T=Kf*m formula. If that's the case then C3H8O3 is the empirical formula and the molecular formula. Correct?

DrBob222 · Answer

Yes, of course you are right. It was way past my bed time and I guess I just punched the wrong numbers on my calculator. The molar mass is 92 and not the 26 I initially calculated and that makes the C3H8O3 ok for the formula.