1. Composition Stoichiometry
Empirical and Molecular Formulas

2. Empirical Formulas
• The lowest whole-number ratio of atoms of
each element in a compound
• May or may not be the same as the molecular
formula of a compound
– Molecular formula shows the actual number of
atoms of each element in a compound
• Can be determined from the percent
composition of the compound

3. What is the empirical formula of a compound that is 62.1% C, 13.8% H, and
24.1% N?
62.1g C 1 molC
C: 5.175molC 1.721mol 3
1 12.0gC
13.8 g H 1 molH
H: 13.8molH 1.721mol 8
1 1.0 g H
24.1 g N 1 mol N
N: 1.721mol N 1.721mol 1
1 14.0 g N
C3H8N

4. A compound is analyzed and found to contain 25.9% nitrogen and 74.1%
oxygen. What is the empirical formula of the compound?
25.9gN 1 mol N
N: 1.85 mol N 1.85mol 1 2 2
1 14.0g N
74.1 g O 1 molO
O: 4.63molO 1.85mol 2.5 2 5
1 16.0g O
N2O5

5. p. 315, #66
Mass of compound sample = 7.36g
Mass of oxygen = 6.93g
Hydrogen is only other element in compound