1. Launch: 12/2
 Grab your binder and immediately take a seat!
 Place homework (practice questions), binder paper, and
a pen/pencil on your desk.
Today’s Objective: I can convert between grams and
atoms using both molecular mass and
Avogadro’s number as a conversion factors
Tonight’s HW: Finish the back of the practice
question worksheet

2. Launch 12/2
4. How many molecules of C3OH are in .5 moles?
a. 3.01 X 1023 molecules
b. 6.02 X 1023 molecules
c. 9.03 X 1023 molecules
d. 1.204 X 1024 atoms

3. Launch 12/2
5. If there are 1.204 X 1024 particles of gold (Au), how
many moles are there?
a. .5 moles
b. 1 mole
c. 2 moles
d. 4 moles

4. Announcements
 Quiz on Friday
 The mole
 Conversions
 Unit exam in 2 weeks

5. How many atoms? – Part II
Mr. Heffner
12/1/09

6. How many atoms?
 Conversion factors… ..or particles, or molecules
 are used to convert one unit to another unit
sum of
atomic Molar Mass Avogadro’s #
masses
? grams/mole 6.02 X 1023 atoms/mole
? grams 6.02 X 1023 atoms
1 mole 1 mole
1 mole 1 mole
? grams 6.02 X 1023 atoms
Grams  Moles Atoms  Moles

7. How many atoms?
 What if we want to convert grams  atoms?
 Need to use both conversion factors!

8. How many atoms?
 There is a 3-step process for conversions:
1. Write down the starting unit and look at the ending unit.
2. Write the conversion factor with the starting units on the
bottom.
 If grams, start with molar mass
 If atoms (or particles, or molecules), start with Avogadro’s #
3. Cancel like terms and multiply across the top and bottom.

9. Example #1
How many atoms are there in 12.01 grams of carbon (C)?
 Step #1: Write down the starting unit and look at the
ending unit.
12.01 grams

10. Example #1
How many atoms are there in 12.01 grams of carbon (C)?
 Step #2: Write the conversion factor with the starting units
on the bottom.
1 mol 6.02 X 1023 atoms
12.01 g X X =
12.01 g 1 mol
Start with Then use
molecular Avogadro’s #
mass

11. Example #1
How many atoms are there in 12.01 grams of carbon (C)?
 Step #3: Cancel like terms and multiply across the top
and bottom
1 mol 6.02 X 1023 atoms
12.01 g X X =
12.01 g 1 mol
Ignore
1 X 6.02 X 1023 atoms
=
1
6.02 X 1023 atoms =

12. Example #3
How many grams of CH4 are there in 12.04 X 1023 molecules?
Step #1: Write down the starting unit and look at the ending
unit.
12.04 X 1023 molecules

13. Example #3
How many grams of CH4 are there in 12.04 X 1023 molecules?
 Step #2: Write the conversion factor with the starting units
on the bottom.
1 mol 16.05 g
12.04 X 1023 molecules X X
1 mol
=
6.02 X 10 23 molecules
Then use
Start with molecular
Avogadro’s # mass

14. Example #3
How many grams of CH4 are there in 12.04 X 1023 molecules?
 Step #3: Cancel like terms and multiply across the top
and bottom
1 mol 16.05 g
12.04 X 1023 molecules X X
1 mol
=
6.02 X 10 23 molecules
12.04 X 1 X 16.05 g
=
6.02 X 1
32.10 g = 2 X 16.05 g =

15. Example #2
How many atoms are there in 16.00 grams of O2?
 Step #1: Write down the starting unit and look at the
ending unit.
16.00 grams

16. Example #2
How many atoms are there in 16.00 grams of O2?
 Step #2: Write the conversion factor with the starting units
on the bottom.
1 mol 6.02 X 1023 atoms
16.00 g X X =
32.00 g 1 mol
Start with Then use
molecular Avogadro’s #
mass

17. Example #2
How many atoms are there in 16.00 grams of O2?
 Step #3: Cancel like terms and multiply across the top
and bottom
1 mol 6.02 X 1023 atoms
16.00g X X =
32.00 g 1 mol
Ignore
16.00 X 6.02 X 1023 atoms
=
32.00 X 1
3.01 X 1023 atoms = .5 X 6.02 X 1023 atoms =

18. Whiteboards
 Work in pairs
 Trade-off marker every question
 You have 60 seconds to solve the question
 Show all of your work!
 Don’t forget units!
 Lift board only when prompted

19. How many atoms are there in
8.00 grams of helium (He) ?

20. How many molecules are
there in 4.04 grams of H2?

21. What is the mass (in grams)
of 6.02 X 10 23 particles
of gold (Au)?

22. How many grams does
3.01 X 1023 molecules
of HCl weight?

23. Practice Questions
 Practice question worksheet

24. Exit Slip
1. Which conversion factor would need to be used to
convert between gramsmoles?
a. Avogadro’s number
b. 6.02 X 1023 atoms/mole
c. Molecular mass
d. Atomic weight

25. Exit Slip
2. Which conversion factor would need to be used to
convert grams into atoms?
a. Avogadro’s number
b. Atomic weight
c. Molecular mass
d. both a & c

26. Exit Slip
3. Which of the following correctly shows how to convert
64.00g of O2 to atoms?
6.02 X 1023 atoms
a. 32.00g X
32.00g
1 mole
b. 64.00g X 32.00 g
1 mole 6.02 X 1023 atoms
c. 64.00g X 32.00 g X 1 mole
1 mole 1 atoms
d. 64.00 g X X
6.02 X 10 23 g
32.00 moles

27. Exit Slip
4. How many atoms of nitrogen (N) are there in 14.01g?
a. 3.01 X 1023 atoms
b. 6.02 X 1023 atoms
c. 9.03 X 1023 atoms
d. 1.204 X 1024 atoms

28. Exit Slip
5. How many grams does 12.04 X 1023 molecules of
H2O weigh?
a. 9.01g
b. 18.02g
c. 27.03g
d. 36.04g

29. Homework
 Finish practice questions
 Study for Friday’s Quiz!