1. 7.1 and 7.2 Review Calculate the mass in grams of 3.42 x 10 24 molecules of NaCl. Calculate the volume occupied by 100g of water vapor (H 2 O)

2. 7.1 and 7.2 Review Calculate the mass in grams of 3.42 x 10 24 molecules of NaCl. 329.5 g Calculate the volume occupied by 100g of water vapor (H 2 O) 124.4 L

3. 7.3 Percent Composition

4. Percent Composition When showing the amounts of each element present in a compound using percentage by mass % mass of element A = grams of element A x 100% grams of compound

5. Example Problem: What is the percent composition of Aluminum, when 2.64 g of aluminum combine with oxygen to form 5.10 g of aluminum oxide. % mass of element A = grams of element A x 100% grams of compound % comp Al = 2.64 g Al x 100 = 51.8% Al 5.10 g Al 2 O 3

6. Your Turn: What is the percent composition of aluminum and oxygen, when 8 g of Al combine with O 2 to form 13.75 g of aluminum oxide.

7. 8 g Al x 100 = 58% Al 13.75 g Al 2 O 3 42 % O 2

8. We can also calculate the percent composition of each element using the molar mass!!! Example: What is the percent composition of Iron and Oxygen in Fe 2 O 3 ? Mass Fe (55.85g )2 = 111.7g + Mass O + (16 g)3 = 48 g Mass Fe 2 O 3 = 159.7 g Know using these values we can determine the % composition!!

9. We can also calculate the percent composition of each element using the molar mass!!! Example: What is the percent composition of Iron and Oxygen in Fe 2 O 3 ? % Fe = 111.7g x 100 = 69.9% Fe 159.7 g % O = 48 gx 100 = 30.1% 159.7 g

10. Know it’s your turn: Determine the % composition of each element in Ag 2 O.

11. The End!!!