The document discusses empirical and molecular formulas. It provides that empirical formulas show the lowest whole number ratio of elements in a compound and may not reflect the actual number of atoms, while molecular formulas show the exact number of each atom. It then gives examples of determining the empirical formula of compounds from their percent composition and finding that the empirical formulas are C3H8N and N2O5.

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