Vanillin contains 63.15% C, 5.30%H, and oxygen. What is the empirical formula of vanillin?

Answer 1

Take 100 g sample which will contain 63.15 g C, 5.30 g H, and 31.6 g oxygen.
Convert to mols. mols = grams/atomic mass
63.15/12 = 5.26 mols C
5.30/1 = 5.30 mols H
31.6/16 = 1.98 mols O
Now you want to find the ratio of these elements to one another with none smaller than 1. The easy way to do that is to divide all of the numbers by the smallest one; i.e., that of C, so
5.26/1.98 = 2.66 C
5.30/1.98 = 2.68 2.68 H
1.98/1.98 = 1.00 O but C and H are too far from a whole number. What we do in these situations is to multiply by whole numbers until we get close to a whole number for C and H.
by 2 gives us
C = 2.66 x 2 = 5.32
H = 2.68 x 2 = 5.36
O = 1.00 x 2 = 2.00
Doesn't work so multiply by 3
C = 2.66 x 3 = 7.98
H = 2.68 x 3 = 8.04
O = 1.00 x 3 = 3.00
So the empirical formula must be C8H8O3. Check my work.