1. Chapter 7 Lesson 2 Chemical Quantities

2. Mass-Mole Calculations What is the mass of 1.33 moles of titanium, Ti? What is the mass of 1.33 moles of titanium, Ti? We want grams, we have 1.33 moles of titanium. We want grams, we have 1.33 moles of titanium. Use the molar mass of Ti: 1 mol Ti = 47.88 g Ti Use the molar mass of Ti: 1 mol Ti = 47.88 g Ti = 63.7 g Ti 1.33 mole Ti × 47.88 g Ti 1 mole Ti

3. Mole Calculations II What is the mass of 2.55 × 10 23 atoms of lead? What is the mass of 2.55 × 10 23 atoms of lead? We want grams, we have atoms of lead. We want grams, we have atoms of lead. Use Avogadro’s number and the molar mass of Pb Use Avogadro’s number and the molar mass of Pb = 87.8 g Pb 2.55 × 10 23 atoms Pb × 1 mol Pb 6.02×10 23 atoms Pb 207.2 g Pb 1 mole Pb ×

4. Mole Calculations II How many O 2 molecules are present in 0.470 g of oxygen gas? How many O 2 molecules are present in 0.470 g of oxygen gas? We want molecules O 2, we have grams O 2. We want molecules O 2, we have grams O 2. Use Avogadro’s number and the molar mass of O 2 Use Avogadro’s number and the molar mass of O 2 8.84 × 10 21 molecules O 2 0.470 g O 2 × 1 mol O 2 32.00 g O 2 6.02×10 23 molecules O 2 1 mole O 2 ×

5. Gas Density The density of gases is much less than that of liquids. The density of gases is much less than that of liquids. We can calculate the density of any gas at STP easily. We can calculate the density of any gas at STP easily. The formula for gas density at STP is: The formula for gas density at STP is: = density, g/L molar mass in grams molar volume in liters

6. Calculating Gas Density What is the density of ammonia gas, NH 3, at STP? What is the density of ammonia gas, NH 3, at STP? First we need the molar mass for ammonia; First we need the molar mass for ammonia; 14.01 + 3(1.01) = 17.04 g/mol 14.01 + 3(1.01) = 17.04 g/mol The molar volume NH 3 at STP is 22.4 L/mol. The molar volume NH 3 at STP is 22.4 L/mol. Density is mass/volume: Density is mass/volume: = 0.761 g/L 17.04 g/mol 22.4 L/mol

7. 7 Molar Volume At standard temperature and pressure (STP), 1 mole of a gas occupies a volume of 22.4 L, which is called its molar volume.

8. Molar Mass of a Gas We can also use molar volume to calculate the molar mass of an unknown gas. We can also use molar volume to calculate the molar mass of an unknown gas. 1.96 g of an unknown gas occupies 1.00L at STP. What is the molar mass? 1.96 g of an unknown gas occupies 1.00L at STP. What is the molar mass? We want g/mol, we have g/L. We want g/mol, we have g/L. 1.96 g 1.00 L 22.4 L 1 mole ×= 43.9 g/mol

9. Mole Unit Factors We now have three interpretations for the mole: We now have three interpretations for the mole: 1 mol = 6.02 × 10 23 particles 1 mol = 6.02 × 10 23 particles 1 mol = molar mass 1 mol = molar mass 1 mol = 22.4 L at STP for a gas 1 mol = 22.4 L at STP for a gas This gives us 3 unit factors to use to convert between moles, particles, mass, and volume. This gives us 3 unit factors to use to convert between moles, particles, mass, and volume.

10. Mole-Volume Calculation A sample of methane, CH 4, occupies 4.50 L at STP. How many moles of methane are present? A sample of methane, CH 4, occupies 4.50 L at STP. How many moles of methane are present? We want moles, we have volume. We want moles, we have volume. Use molar volume of a gas: 1 mol = 22.4 L Use molar volume of a gas: 1 mol = 22.4 L 4.50 L CH 4 ×= 0.201 mol CH 4 1 mol CH 4 22.4 L CH 4

11. Mass-Volume Calculation What is the mass of 3.36 L of ozone gas, O 3, at STP? What is the mass of 3.36 L of ozone gas, O 3, at STP? We want mass O 3, we have 3.36 L O 3. We want mass O 3, we have 3.36 L O 3. Convert volume to moles then moles to mass: Convert volume to moles then moles to mass: = 7.20 g O 3 3.36 L O 3 ×× 22.4 L O 3 1 mol O 3 48.00 g O 3 1 mol O 3

12. Molecule-Volume Calculation How many molecules of hydrogen gas, H 2, occupy 0.500 L at STP? How many molecules of hydrogen gas, H 2, occupy 0.500 L at STP? We want molecules H 2, we have 0.500 L H 2. We want molecules H 2, we have 0.500 L H 2. Convert volume to moles and then moles to molecules: Convert volume to moles and then moles to molecules: 0.500 L H 2 × 1 mol H 2 22.4 L H 2 6.02×10 23 molecules H 2 1 mole H 2 × = 1.34 × 10 22 molecules H 2

13. Example ■ How many moles of CO 2 gas are in a 2.5 L flask at STP? 2.5 L 1 mol =.11 moles CO 2 22.4 L 22.4 L ■ How many atoms of He are present in a 1.75 L balloon at STP? 1.75 L 1 mole 6.022x10 23 atoms = 4.70x10 23 atoms 22.4 L 1 mole 22.4 L 1 mole