Question

In 1934, Edward A. Doisy of Washington University extracted 3000 lb of hog ovaries to isolate a few milligrams of pure estradiol, a potent female hormone. Doisy burned 5.00 mg of this precious sample in oxygen and found that 14.54 mg of CO2 and 3.97 mg of H2O were generated.

1.) Determine the empirical formula of estradiol.

2.) The molecular weight of estradiol was later determined to be 272. Determine the molecular formula of estradiol.

(express answer as a condensed structural formula and show all of your work, please)

Answer 1

Moles of CO2 = (14.54 mg of CO2)/44.01 g/mol CO2) = 0.3304 mmol CO2
Moles of Carbon = (0.3304 mmol CO2)*(1 mol C/1 mol CO2) = 0.3304 mmol C

Moles of H2O = (3.97 mg of H2O)/(18.0153 g/mol H2O = 0.2204 mmol H2O
Moles of H = (0.2204 mmol H2O)*(2 mole H/1 mol H2O) = 0.4407 mmol H

0.4407 mmol H/0.3304 mmol C = 1.33 => = 4/3 as a ratio of whole numbers (4H/3C)
Therefore, the empirical formula is C3H4
Emperical formula weight of C3H4=40.062 g/formula

n = MF weight/ EF weight = 272/40.062 = 6.78
Round off to 6, so Molecular formula=(C3H4)*6 = C18H24 .
Molecular formula weight= 6*(40.062 g/formula) = 240 g/formula
Mass difference = 272-240 = 32
A mass of 32 would exactly correspond to that of 2 oxygen molecules, so the proposed molecular formula is
C18H24O2