1. 4.3  APPLICATION EXAMPLE FOR MOLES  Gas Behavior How does the behavior of gases affect airbags?

2. What is pressure? Pressure – Force of gas particles running into a surface

3. As number of molecules increases, there are more molecules to collide with the wall Collisions between molecules and the wall increase Pressure increases If pressure is molecular collisions with the container… As # of molecules increases, pressure increases Pressure and Number of Molecules

4. Pressure and Volume As volume increases, molecules can travel farther before hitting the wall Collisions between molecules and the wall decrease Pressure decreases If pressure is molecular collisions with the container… As volume increases, pressure decreases

5. Section 4.3—Counting Molecules So the number of molecules affects pressure of an airbag…how do we “count” molecules?

6. How do auto makers utilize enough atoms of gas to create pressure that inflates the bag, But not so many that the pressure is too great when it hits you and your face that it causes permanent damage Count the atoms

7. What is a mole?

8. Definition Mole – SI unit for counting The only acceptable abbreviation for “mole” is “mol”…not “m”!!

9. What is a counting unit? You’re already familiar with one counting unit…a “dozen” “Dozen”12 A dozen doughnuts 12 doughnuts A dozen books A dozen cars A dozen people 12 books 12 cars 12 people A dozen = 12

10. What does a “mole” count in? A mole = 6.02  10 23 (called Avogadro’s number) “mole” 6.02  10 23 1 mole of doughnuts 6.02  10 23 doughnuts 1 mole of atoms 1 mole of molecules 6.02  10 23 atoms 6.02  10 23 molecules 6.02  10 23 = 602,000,000,000,000,000,000,000 This means a 12 ounce bottle of water would have 19.7 “moles” of water…a much easier-to-work-with number!

11. Molar Mass

12. Definition Molar Mass – The mass for one mole of an atom or molecule. Other terms commonly used for the same meaning: Molecular Weight Molecular Mass Formula Weight Formula Mass

13. Mass for 1 mole of atoms The average atomic mass = grams for 1 mole ElementMass 1 mole of carbon atoms 12.01 g 1 mole of oxygen atoms 1 mole of hydrogen atoms 16.00 g 1.01 g Unit for molar mass: g/mole or g/mol Average atomic mass is found on the periodic table

14. Molar mass for molecules The molar mass for a molecule = the sum of the molar masses of all the atoms

15. Calculating a Molecule’s Mass Count the number of each type of atom Find the molar mass of each atom on the periodic table Multiple the # of atoms  molar mass for each atom Find the sum of all the masses 1 2 3 4 To find the molar mass of a molecule:

16. Example: Molar Mass Example: Find the molar mass for CaBr 2

17. Example: Molar Mass Count the number of each type of atom 1 Ca Br 1 2 Example: Find the molar mass for CaBr 2

18. Example: Molar Mass Find the molar mass of each atom on the periodic table 2 Ca Br 1 2 40.08 g/mole 79.91 g/mole Example: Find the molar mass for CaBr 2

19. Example: Molar Mass Multiple the # of atoms  molar mass for each atom 3 Ca Br 1 2 40.08 g/mole 79.91 g/mole   Example: Find the molar mass for CaBr 2 = 40.08 g/mole = 159.82 g/mole

20. Example: Molar Mass Find the sum of all the masses 4 Ca Br 1 2 40.08 g/mole 79.91 g/mole = 40.08 g/mole = 159.82 g/mole + 199.90 g/mole 1 mole of CaBr 2 molecules would have a mass of 199.90 g Example: Find the molar mass for CaBr 2  

21. Example: Molar Mass & Parenthesis Be sure to distribute the subscript outside the parenthesis to each element inside the parenthesis. Example: Find the molar mass for Sr(NO 3 ) 2

22. Example: Molar Mass & Parenthesis Be sure to distribute the subscript outside the parenthesis to each element inside the parenthesis. 1 6 87.62 g/mole 16.00 g/mole   = 87.62 g/mole = 96.00 g/mole + 211.64 g/mole 1 mole of Sr(NO 3 ) 2 molecules would have a mass of 211.64 g 214.01 g/mole  = 28.02 g/mole Sr N O Example: Find the molar mass for Sr(NO 3 ) 2

23. Let’s Practice #2 Example: Find the molar mass for Al(OH) 3

24. Let’s Practice #2 Be sure to distribute the subscript outside the parenthesis to each element inside the parenthesis. 1 3 26.98 g/mole 1.01 g/mole   = 26.98 g/mole = 3.03 g/mole + 78.01 g/mole 1 mole of Al(OH) 3 molecules would have a mass of 78.01 g 316.00 g/mole  = 48.00 g/mole Al O H Example: Find the molar mass for Al(OH) 3

25. Using Molar Mass in Conversions

26. Example: Moles to Grams Example: How many grams are in 1.25 moles of water?

27. Example: Moles to Grams 1.25 mol H 2 O = _______ g H 2 O mol H 2 O g H 2 O 18.02 1 22.53 When converting between grams and moles, the molar mass is needed 1 mole H 2 O molecules = 18.02 g H O 2 1 1.01 g/mole 16.00 g/mole  = 2.02 g/mole = 16.00 g/mole + 18.02 g/mole  Example: How many grams are in 1.25 moles of water?

28. Let’s Practice #3 Example: How many moles are in 25.5 g NaCl?

29. Let’s Practice #3 25.5 g NaCl = _______ mole NaCl g NaCl mole NaCl 1 58.44 0.44 1 mole NaCl molecules = 58.44 g Na Cl 1 1 22.99 g/mole 35.45 g/mole  = 22.99 g/mole = 35.45 g/mole + 58.44 g/mole  Example: How many moles are in 25.5 g NaCl?

30. Let’s Practice #4 Example: How many grams is a sample of 2.75 × 10 24 molecules of SrCl 2 ?

31. 2.75 × 10 24 molecules SrCl 2 Let’s Practice #4 = _________ g SrCl 2 molecules SrCl 2 mol SrCl 2 1 6.02 × 10 23 7.24 1 mol = 6.02  10 23 molecules 1 moles SrCl 2 molecules = 158.52 g Sr Cl 1 2 87.62 g/mole 35.45 g/mole  = 87.62 g/mole = 70.90 g/mole + 158.52 g/mole  mol SrCl 2 g SrCl 2 158.52 1 Example: How many grams is a sample of 2.75 × 10 24 molecules of SrCl 2 ?

32. Example: Grams to Molecules Example: How many molecules are in 25.5 g NaCl?

33. 25.5 g NaCl Example: Grams to Molecules = _________ molecules NaCl g NaCl mol NaCl 1 58.44 2.63  10 23 1 mol = 6.02  10 23 molecules 1 moles NaCl molecules = 58.44 g Na Cl 1 1 22.99 g/mole 35.45 g/mole  = 22.99 g/mole = 35.45 g/mole + 58.44 g/mole  mol NaCl molecules NaCl 6.02  10 23 1 Example: How many molecules are in 25.5 g NaCl?