Question

Caffeine has the following percent composition: carbon 49.48%, hydrogen 5.19%, oxygen 16.48% and nitrogen 28.85%. Its molecular weight is 194.19 g/mol. Find both the empirical formula and the molecular formula. Fill in the blanks for the subscripts in the formulas below. Fill in for all of the subscripts if the subscript is 1.

empirical formula = C  H  N  O

molecular formula = C  H  N  O

Answer 1

Empirical formulas tell you the simplest or most reduced ratio of elements in a compound. For example for the molecular formula C5H,0 simplest ratio will be CH2 and hence empirical formula of cyclopentane is CH2 Empirical formula from the percentages of given elements can be derived as shown below number of moles (n) = Percentage of the element Molecular weight of the element C, n 49.48 / 12 = 4.12 H, n 5.19/1 5.19 O, n 16.48 / 16= 1.03 N,n 28.85/ 14 2.06 After calculating the number of moles (n) values, Divide each mole value by the smalllest number of moles calculated Here smallest number of moles is 1.03 n 4.12/1.03 4 C , H, n 5.19 1.03 5 O,n 1.03/1.03 = 1 N,n 2.06/1.03 2 Empirical formula is C4H5N2O Given molecular weight is 194.19 g/mol 2 (C4H5N20) C3H10N02 caffeine C4HgN2O Molecular Weight: 97.10 caffeine molecular formula = CgH10N402