1. Molar Volume of Gases, Percent Composition, Empirical/ Molecular Formula Finishing Up Ch. 10

2. In 1811, Avogadro proposed a hypothesis: – Volumes of gases at the same temp and pressure have the same number of particles https://www.youtube.com/watch?v=CKs4WKv 6foI https://www.youtube.com/watch?v=CKs4WKv 6foI Check it out!

3. Mass  Moles  Volume Volumes of 1 mole of different solid or liquid substances are not the same. Gases are a different story! With varying temperature, volume of gases change. But at STP (0 deg C and 1 atm), 1 mol of ANY gas, has a volume of 22.4 L. Molar volume of a gas = 22.4 L

4. Calculating the Volume of a Gas at STP Volume of a gas = Moles of gas X 22.4 L 1 mole

5. Practice Sulfur dioxide is a gas produced by burning coal. It is an air pollutant and one of the causes of acid rain. Determine the volume, in L, of 0.60 mol sulfur dioxide gas at STP.

6. Practice What is the volume of these gases at STP? – 3.20 x 10 -3 mol CO 2 – 3.7 mol N2

7. Check out the Mole Road Map on page 303!

8. Percent Composition by Mass When a 13.60 g sample of a compound containing only magnesium and oxygen is decomposed, 5.40 g of oxygen is obtained. What is the percent composition of this compound?

9. Practice: Calculate the Percent Composition by Mass of Sulfur in Calcium Sulfite

10. Empirical Formula The empirical formula shows the lowest whole number ratio of atoms in a compound. Ex: Hydrogen peroxide

11. Solving for Empirical Formula -Find moles of each component by using each one’s mass -Divide each by smallest number of moles -Multiply each if necessary to obtain whole numbers

12. Practice: A compound is analyzed and found to contain 25.9% nitrogen and 74.1% oxygen. What is the empirical formula for the compound?

13. Practice 1,6 diaminohexane is used to make nylon. What is the empirical formula of this compound if it is 62.1% C, 13.8% H, and 24.1% N?

14. Molecular Formula The molecular formula of a compound is either the same as its empirical formula, or it is a simple whole-number multiple of its empirical formula.

15. To find Molecular formula: -Find molar mass of the empirical formula -Divide the given molar mass by the empirical molar mass to get a whole number -Finally, multiply this whole number by each subscript in the formula

16. Practice Calculate the molecular formula of a compound whose molar mass is 60.0 g/mol and empirical formula is CH 4 N.

17. Try it Find the molecular formula of ethylene glycol (antifreeze). The molar mass is 62 g/mol and the empirical formula is CH 3 O.

18. Practice makes Perfect HW- practice 32-37