1. Measuring Chemical Quantities

2. Ways to Count
Term
# Items
Pair
Quartet
Octet
Dozen
Ream
Gross
Case

3. Ways to Count
Each of the relationships on the previous page can be written as an equality and used to create conversion factors
These relationships are common place and we perform these calculations without much thought

4. Ways to Count
Class Exercise

5. Ways to Count
Methane Molecules

6. Counting Atoms and Molecules
Atoms and molecules are very small
Reactions happen at the particle level so number of atoms and molecules is important
Term introduced to represent a specific quantity of atoms or molecules
The chemists “dozen”

7. The Mole
1 mole = 6.02 x 1023 particles
Avogadro’s Number (N)

8. The Mole
The number equal to the number of carbon atoms in exactly 12 grams of carbon-12.
One mole of a substance contains 6.02 x 1023 particles of that substance.

9. How big is a mole? + A mole of….
sand grains would cover the US in ~ 1 cm of sand
cells is about the number of cells in the human body
grapefruit would have approximately the same volume as the Earth (~500 large grapefruit will fit in 1 cubic meter; VEarth = 1.1 x 1012 km3)
dollars would take 20 billion years to spend at 1 million dollars a second
data from Wikipedia 12/28/06, updated 12/22/06 and Flinn ChemFax, 10/27/03

10. Mass Ratios # C atoms Mass (amu) # H atoms mass C mass H Mass Ratio 1
1 x 12
= 12
1 x 1
= 1
12 amu
1 amu 12 2
2 x 12
= 24
2 x 1
= 2
24 amu
2 amu 10
10 x 12
=120
10 x 1
=10
120 amu
10 amu
6.02 x 1023 (N)
N x 12
6.02 x 1023
(N)
N x 1
N x 12 amu
N x 1 amu

11. Conclusion
Average atomic mass of any element in grams is the mass of one mole of that element
1 mole C = g
1 mole Mg = g
1 mole S = g

12. Terms Synonyms: Definitions: gram atomic mass gram atomic weight
molar mass
Definitions:
Gram atomic mass is the mass, in grams, of one mole of the element
Molar mass is the mass, in grams, of one mole of a substance

13. Counting by Weighing Establish number of items in a given weight
M&Ms are sold by weight but there are ~same number of M&Ms per package
Aspirin is sold by number, but the bottles can be filled by weight, rather than by counting
average atomic mass can help us count atoms

14. 1 mole = average atomic mass (in grams)
Mole Calculations
Two relationships:
1 mole = 6.02 x 1023 atoms
1 mole = average atomic mass (in grams)
Use these relationships to form conversion factors
Mole calculations are just like converting from miles to meters or grams to pounds

15. Mole Relationships Particles 1 mole = 6.02 x 1023 Mole Volume Mass
1 mole = 22.4 L
At STP
1 mole = molar mass
(in grams)

16. Pathways to Calculating Moles-Mass-Number
molar mass
1 mole
1 mole
molar mass
6.02x1023 particles
1 mole
1 mole
6.02x1023 particles
Mass
# Particles