7.2

1. 7.2 More Mole Conversions!!!

2. Molar Mass • The mass in grams of 1 mol of a substance. • Calculated using the periodic table!!! Example: What is the molar mass of N2, nitrogen gas? 2 (14g) = 28 g

3. Another Example • What is the molar mass of molecular oxygen, O2? 2 (16g) = 32 g

4. 7 elements that exist as diatomic molecules: H2 F2 O2 N2 Cl2 Br2 I2

5. Knowing molar mass is important because it allows us to make the following conversions: mass mol representative particle

6. 1 mol of a substance = molar mass of a substance Example: What is the molar mass of nitrogen gas, N2? 1 mol N2 28 g N2

7. Ex. 1 Example problem • How many grams are in 2 mol of nitrogen gas? • Given: 2 mol N2 • Known: 1 mol N2= 28g N2 Mol  mass 2 mol N2 28 g N2 = 56 g N2 1 mol N2

8. EX.2 How many molecules are in 84 g of nitrogen gas? • Given: 84 g N2 • Known: 1 mol N2 = 28 g N2 1 mol N2 = 6.02 x 1023 molecules N2 Mass  mol  molecules

9. How many molecules are in 84 g of nitrogen gas? • Given: 84 g N2 • Known: 1 mol N2 = 28 g N2 1 mol N2 = 6.02 x 1023 molecules N2 Mass  mol  molecules 84 g N2 1 mol N2 6.02 x 1023 molecules N2 28 g N2 1 mol N2 = 1.806 x 1024 molecules

10. Your Turn Ex.3: Find the number of moles in 176 g of CO2. • Given: • Known: Road Map:

11. Your Turn Ex.3: Find the number of moles in 176 g of CO2. • Given: 176 g CO2 • Known: 44 g CO2 = 1 mol CO2 Road Map: Mass  Mol

12. Your Turn Ex.3: Find the number of moles in 176 g of CO2. • Given: 176 g CO2 • Known: 44 g CO2 = 1 mol CO2 Road Map: Mass  Mol 176 g CO2 1 mol CO2 = 4 mol CO2 44 g CO2

13. Ex. 4 Find the mass of 1.2 x 1024 molecules of NaCl Given: 1.2 x 1024 molecules NaCl Known: Road Map:

14. Ex. 4 Find the mass of 1.2 x 1024 molecules of NaCl Given: 1.2 x 1024 molecules NaCl Known: 1 mol = 6.02x1023 molecules NaCl 1 mol NaCl = 58 g NaCl Road Map: Molecules  mol  mass

15. Ex. 4 Find the mass of 1.2 x 1024 molecules of NaCl Given: 1.2 x 1024 molecules NaCl Known: 1 mol = 6.02x1023 molecules NaCl 1 mol NaCl = 58 g NaCl Road Map: Molecules  mol  mass 1.2 x 1024 molecules NaCl 1 mol NaCl 58 g NaCl 6.02x1023 molecules 1 mol NaCl NaCl

16. Volume of 1 mol of a gas: At STP (standard temperature and pressure) • 0°C or 273 K • 1 atm or 101.3 kPa 1 mol of a gas occupies 22.4 L 1 mol or 22.4 L 22.4L 1 mol

17. Ex. 5 Determine the volume in L of 2 mol of oxygen gas at STP. • Given: 2 mol O2 • Known: 1 mol O2 = 22.4 L Work:

18. Ex. 5 Determine the volume in L of 2 mol of oxygen gas at STP. • Given: 2 mol O2 • Known: 1 mol O2 = 22.4 L Work: 2 mol O2 22.4 L = 44.8 L O2 1 mol O2

19. Your turn! Ex. 6 Determine the number of moles in 67.2 L of oxygen gas. • Given: 67.2 L O2 • Known:

20. Your turn! Ex. 6 Determine the number of moles in 67.2 L of oxygen gas. • Given: 67.2 L O2 • Known: 1 mol O2 = 22.4 L Work 67.2 L O2 1 mol O2= 3 mol O2 22.4 L

21. Now we have a big road map…. Volume (L) # representative Mass moles particles

22. Ex. What is the volume of 8 g of O2? Given: 8 g of O2 Known:

23. Ex. What is the volume of 8 g of O2? Given: 8 g of O2 Known: 1 mol O2 = 32 g O2 1 mol O2 = 22.4 L Road Map: Mass  Mol  volume 8 g of O2 1 mol O2 22.4 L = 5.6 L 32 g O2 1 mol O2

24. How much volume does 1.8 x 1024 molecules of Cl2 at STP occupy? Road Map Molecules  mol  volume

25. How much volume does 1.8 x 1024 molecules of Cl2 at STP occupy? Road Map Molecules  mol  volume 1.8 x 1024 molecules of Cl21 mol Cl222.4 L 6.02 x 1023 Cl2 1 mol Cl2 = 67.2 L

26. Density: mass/volume • grams / L • When given density, you can calculate molar mass using the volume of 1 mol. g 22.4 L g L 1 mol mol

27. The End!!!