1. The Calculation of Formula Weight !!!
very exciting!!

2. The definition of Formula Weight !!!
Formula weight is the total weight of all of the atoms in a chemical formula…

3. NaNO3 Example: Sodium nitrate has the formula: Symbols
Oxidation states
Criss – cross
Reduce

4. NaNO3 You can picture this molecule as having the following structure:

5. From the periodic chart
Each of the atoms in the formula has its own atomic weight… 14 16 23 O N Na O
From the periodic chart O

6. So we can find the formula weight by adding up all of the weights of the individual atoms…Na O O
becomes
1(23) + 1(14) + 3(16) = 85

7. This result is called the formula weight of this compound

8. Al2(SO4)3 Another Example: from: Symbols Oxidation States Criss-Cross
The compound aluminum sulfate has the formula:
from:
Symbols
Oxidation States
Criss-Cross
Reduce
Al2(SO4)3

9. fw = Σ ( inventory x atomic weight)
To calculate the formula weight of this compound we will use the strategy:
fw = Σ ( inventory x atomic weight)
… which is formula weight equals the sum of the inventory multiplied by the atomic weight…

10. Al2(SO4)3 Inventory Atomic Weight 27.0 32.1 16.0 Aluminum = 2
For aluminum sulfate, that works out like this:
Al2(SO4)3
Inventory
Atomic Weight
27.0
32.1
16.0
Aluminum = 2
Sulfur = 3
Oxygen = 12

11. The units are grams/mole
… finishing this up gives … Al S O
2(27.0) + 3(32.1) (16.0) =
342.3
The units are grams/mole