What is the empirical formula?

Question

A laboratory analysis of vanillin, the flavoring agent in vanilla, determined the following mass percent composition: 63.15 % carbon, 5.30 % hydrogen and 31.55 % oxygen. What is the empirical formula of vanillin?

How to solve this question?

Answer 1

Suppose you had 10,000 atomic mass units (u) of vanillin. This sample would contain:

6315 u carbon

530 u hydrogen

3155 u oxygen

We can then divide these masses by the atomic masses found in the periodic table to find the number of C, H, and O atoms are in the sample.

C: 6315 u / (12.011 u / atom) ≈ 526 atoms

H: 530 u / (1.008 u / atom) ≈ 526 atoms

O: 3155 u / (15.999 u / atom) ≈ 197 atoms

The ratio of 526:197 is very close to 8:3, so an empirical is C₈H₈O₃