1. Percent Composition

2. Percent Composition The gram formula mass of a compound represents the TOTAL MASS of the compound What percent of the total mass is each element in the compound? Remember: percent means “out of 100”

3. For example…. This cup contains a total mass of 100 g of liquid. 75 g are “coffee” and 25 g are “cream”. What is the percent composition of the liquid in the cup? 75g coffee x 100 = 75% coffee 100g total 25g cream x 100 = 25% cream 100g total

4. What is the percent composition of potassium chlorate? Formula = KClO3 Gram Formula Mass : K = 1 x 39 = 39 Cl = 1 x 35.5 = 35.5 O = 16 x 3 = 48 +______ 122.5 g What percent of the total mass (122.5 g) is each of the elements (K, Cl, and O) in the compound?

5. 39 g x 100 = 31.8 % 122.5 g K = 39 g 35.5 g x 100 = 29.0 % 122.5 g Cl = 35.5 g 48 g x 100 = 39.2 % 122.5 g O3 = 48 g + ________ 100 %

6. Percent composition formula is in Table T (back page) mass of part x 100 mass of whole

7. You try it! What is the percent composition of MgBr2? Mg = 24 g x 1 = 24 g Br = 80 g x 2 = 160g +_____ 184 g Mass of whole % Mg 24 g (mass of part) x 100 = 13.0 % 184 g % Br 160 g x 100 = 87.0 % 184 g

8. % Composition and Hydrates Same as other compounds, except treat the “water” as a part: What is the % composition of water in the hydrated compound Na2CO3• 10 H2O

9. Na2CO3• 10 H2O Total mass (GFM) = 286 g Mass of water (the “part”) = 10 x 18g = 180 g % composition of water = 180 g x 100 = 62.9 % water 286 g

10. You try it! What is the percent composition of water and calcium sulfate in the hydrated compound CaSO4 • 2H2O 21 % water 79 % calcium sulfate