posted by Monique on .
Caffeine a stimulant found in coffee has the mass composition of C, 49.48%, H, 5.19%, N, 28.85%, O 16.48%. The molar mass of caffeine is 194.19g/mol. Find the molecular formula for caffeine.
Take 100 g sample which gives you
5.19 g H
Now convert grams to moles with moles = grams/molar mass
Then find the ratio of the elements to the smallest one with it being no less than 1.00. The easy way to do that is to divide the smallest number by itself (thereby assuring a 1.00 for that element), then divide all of the other numbers by the same small number, round to whole numbers, and that should be the empirical formula. Check the mass of the empirical formula to see if the molar mass is 1x, 2x, 3x, etc of the empirical mass. I worked it and found the empirical formula of C4H5N2O.
I got that as well but then I took the molar mass and divided by the empirical formula and got C8H10N4O2
C8H10N4O2 is the molecular formula.