Acetaminophen as a chemical formula of C8H9NO2. The molar masses are:
C8H9NO2 = 151.163 g/mol
C = 12 g/mol
H = 1 g/mol
N = 14 g/mol
O = 16 g/mol
TO get the mass percent, simply multiply the molar mass of each elements with the number of the element divide by the molar mass of acetaminophen, that is:
%C = [(12 * 8) / 151.163] * 100% = 63.50%
%H = [(1 * 9) / 151.163] * 100% = 5.954%
%N = [(14 * 1) / 151.163] * 100% = 9.262%
%O = [(16 * 2) / 151.163] * 100% = 21.17%