%X = masa element X/masa compus din care face parte X * 100
%H = 2/62 * 100 = 3,225 %
%C = 12/62 * 100 = 19,354 %
%O = 3*16/62 * 100 = 77,419 %
62 g H2CO3........3*16 g O
124 g H2CO3..............x g O x = 96 g O
62 g H2CO3.............12 g C
x g H2CO3..............36 g C x = 186 g H2CO3