Question

a .6800g sample of carboxylic acid is burned in oxygen, producing 1.212 g of CO2 and .4991 g of H2O. determine the empirical formula of the carboxylic acid

Answer 1

You have a way to find C and H; the only way to find O is to convert CO2 to C, convert H2O to H, then subtract the sum of C and H from the sample mass to find grams oxygen.

g C = 1.212 x (atomic mass C/molasr mss CO2) = estimated 0.33
g H = 0.4991 x (2*atomic mass H/molar mass H2O) = estimated 0.055
g O = 0.68-gC-gH = estimated 0.3

Convert grams to mols.
C = grams/12 = est 0.27
H = 0.055/1 = about 0.055
O = 0.3/16 = about 0.018

Then find the ratio of these numbers to each other.
I found C = 1.5
H = 3
O = 1 and these are clearly in the ratio of
C = 3, H = 6, O = 2.
That fits for CH3CH2COOH
(Carboxylic acids are R-COOH and the R in this case is CH3CH2.)