1. Formula Weights and Percentage Composition
Section 3.3
Formula Weights and Percentage Composition

2. Formula Weights
Sum of the atomic weights of each atom in its chemical formula
We did this with empirical/molecular problems
Formula Weights are also Molecular Weights for molecules

3. Molecular Weights
How do we calculate the molecular weight of a compound?
add atomic weights of each atom
The molecular weight of propane, C3H8, is: 32

4. Molecular Weights
The molecular weight of calcium nitrate, Ca(NO3)2 , is:
You do it! 32

5. Formula Weights, Molecular Weights, and Moles33

6. Percent Composition
% composition = mass of an individual element in a compound divided by the total mass of the compound x 100%
Determine the percent composition of C in C3H8. 45

7. Percent Composition and Formulas of Compounds
What is the percent composition of H in C3H8?
You do it! 46

8. Percent Composition and Formulas of Compounds
What is the percent composition of H in C3H8? 47

9. Percent Composition and Formulas of Compounds
Example: Calculate the percent composition of Fe2(SO4)3 to 3 significant figures.
You do it! 48

10. Percent Composition and Formulas of Compounds
Example 2-10: Calculate the percent composition of Fe2(SO4)3 to 3 sig. fig. 49

11. Homework
Problems on page 112 in textbook