1. Empirical Formula

2. Percent to mass, Mass to mole, Divide by small, Multiply 'til whole.
Poem for Steps
Percent to mass, Mass to mole, Divide by small, Multiply 'til whole.
**If you have a 100g sample, the percent composition is the same as the mass

3. Example 1
Determine the empirical formula for a compound with the percent composition of 40.00% carbon, 6.72% hydrogen, and 53.28% oxygen.
40.00 g C mol C
12.01 g C
= mol C
3.330
= 1 mol C
6.72 g H mol H
1.01 g H
= mol H
3.330
= mol H ≈ 2 mol H
53.28 g O mol O
16.00 g O
= mol O
3.330
= 1 mol O
E.F. = CH2O

4. Example 2
Determine the empirical formula for methyl acetate, which has the following chemical analysis: 48.64% carbon, 8.16% hydrogen and 43.20% oxygen.
E.F. = C3H6O2

5. Example 3
A 50.0 g sample of a compound contains g Na, g O, and g S. Determine the empirical formula.
E.F. = Na2SO3

6. Example 4
A 50.0 g sample of a compound contains 2.52 g Be, 5.01 g Al, and g Si, and g O. Determine the empirical formula.
E.F. = Be3Al2Si6O18