1. Percent Composition and Empirical Formula

2. Percent Composition General Strategy Convert whole number ratio (moles) to mass percent Formula  Mass Percent

3. Percent Composition Steps Multiply each whole number subscript by the appropriate molar mass. Divide the part of each molecule and divide by the total. Multiply by 100%.

4. Example 1 What is the percentage of each element in SO 2 ?

5. Example 2 What is the percentage of each element in Ca(OH) 2 ?

6. Empirical Formula General Strategy Convert mass percents to whole number ratio (moles) Mass Percent  Formula

7. Empirical Formula Steps Assume each given percentage is a mass Divide each given percentage by the appropriate molar mass. Divide all values by the smallest number of moles to obtain a whole number ratio

8. Empirical Formula Definition: The formula with the simplest whole number ratio. Decimals you should not just round: 0.5 = ½ 0.25 = ¼ 0.33 = 1/3 0.66 = 2/3

9. Molecular Formula Definition: A molecular formula may be simplified to an empirical formula.