The composition by mass of a compound is: C=36.4%, H=6% and F=57.6%. Calculate the empirical formula. If the RFM is 66, what is the molecular formula?

Calculate the moles of each of the 3 elements (to get C=3.03, H=6, F=3.03). Divide these by the smallest mol calculated to get the ratio of the elements. This will get C:H:F as 1:1.978:1 = 1:2:1 and so the empirical formula is CH₂F. The RFM is 66, 66/33 is 2 and so the molecular formula is C₂H₄F₂