1. Section 2: Mass and the Mole
Which one weighs more? Why?
Same number different masses
Same concept in chemistry…
1 mole = x 1023 atoms (single element)
But… atoms are not all the same size. That is why…
1 mol of carbon atoms = 12 g C (Periodic Table)
1 mol of iron atoms = g Fe (Periodic Table)
Same number…different mass

2. Calculating Moles and Mass
1 mol of element = atomic mass of element
1 mol of compound = formula or molar mass of compound
Example
1 mol of Fe = g
1 mol of Na = g
1 mol of carbonic acid (H2CO3) = g (Add Them Together!)
1 mol of sodium chloride (NaCl) =
g (Add Them Together!)

3. Example Calculate the formula mass for ammonia (NH3)
Step Write down the different elements and their atomic mass
N g
H g
Step Count how many of each element is present and multiply the quantity by the atomic mass
N g x 1
H g x 3
= g
= g
Step Add all the totals together
Formula mass = = g

4. Solving the problems Using the Tools
1st…Follow your rules.
1. What do I know?
2. What do I want?
3. How do I get there?(Tools)
You have 2 tools in your tool box!
1 mol Al
6.022 x 1023 particles Al
Avogadro’s #
1 mol Al
107.87g of Ag
107.87g of Al
Molar Mass

5. PRACTICE USING THE TOOLS
Example: Determine the mass in grams of 3.57 mol Al
Follow your rules…
1. What do I know?
2. What do I want?
3. How do I get there?(Tools)
3.57 mols of Al
“Given”
= g of Al
9.63
1 mol Al
6.022 x 1023 particles Al
6.022 x 1023 particles Al
1 mol Al
1 mol Al
26.98 g of Al
26.98 g of Al
1 mol Al

6. PRACTICE USING THE TOOLS
Example: Determine the number of moles 25.5 grams Ag.
Follow your rules…
1. What do I know?
2. What do I want?
3. How do I get there?(Tools)
25.5 g of Ag
“Given”
= mols of Ag
0.236
1 mol Al
6.022 x 1023 particles Al
6.022 x 1023 particles Al
1 mol Al
1 mol Al
107.87g of Ag
107.87g of Al
1 mol Al

7. Example How many mols of oxygen are in 52 g of oxygen
- - -
1 mol O2 x
= mol O2
= 1.6 mol O2
g O2
- - -
Example How many mols of calcium are in 37 g of calcium
37 g Ca
1 mol Ca x
= mol Ca
= mol Ca
40.08 g Ca
Example How many mols of sodium chloride are in g NaCl
100 g NaCl
1 mol NaCl x
= 2 mol NaCl
= mol NaCl
g NaCl

8. Example How many grams of hydrogen are in 1.67 mol of hydrogen
1.67 mol H2
2.016 g H2 x
= g H2
= g H2
1 mol H2
Example How many grams of carbon are in mol of carbon
0.85 mol C
g C x
= 10. g C
= g C
1 mol C
Example How many grams of ammonia are in x 105 mol ammonia
2.3 x 105 mol NH3
g NH3 x
= x 106 g NH3
= 3.9 x 106 g NH3
1 mol NH3

9. Converting Mass and atoms
Golden Rule…GET TO MOLES!!!!
Then you can do what ever you want!
Mass (g)
Moles (mol)
Particles
Example: How many atoms are in 55.2 g Li
55.2 g of Li
“Given”
= mols of Li
7.95
= atoms of Li
4.79 x 1024
1 mol Li
6.022 x 1023 particles Li
6.022 x 1023 particles Li
1 mol Li
1 mol Li
6.94 g of Li
6.94 g of Li
1 mol Li 9

10. Example. An extra strength aspirin tablet contains
Example An extra strength aspirin tablet contains g of aspirin (C9H8O4). How many molecules of aspirin are in one tablet
0.500 g C9H8O4
1 mol C9H8O4
6.022 x 1023 molecules C9H8O4 x x
g C9H8O4
1 mol C9H8O4
= 1.67 x 1021 molecules C9H8O4
= x 1021 molecules C9H8O4
Example In a small firework, x 1022 atoms Sr are used to make the firework burn red. How many grams of strontium are in the firework.
3.467 x 1022 atoms Sr
1 mol Sr
g Sr x x
= g Sr
1 mol Sr
6.022 x 1023 atoms Sr