1 GFW=1 mole = 6.022 X1023 particles
Chemical recipes: How many ways can you cook a mole?
Seriously, stoichiometry is the way we calculate chemical recipes and to make sure that every molecule or ion has a partner. That way we know how much product we will get out of it. Every problem is pretty much the same. Do these steps every time.
The Steps:
1. Correct compound formulas (all charges add to zero)
2. Balanced equation ( same number of same kind of atoms on both sides of the equation)
3. Start with the mass that you are given: the known
4. Calculate the GFW (gram formula weight also known as molar
mass)
5. Divide by GFW to get number of moles present.
6. Multiply by the mole ratio (the ratio from the balanced equation telling you how much unknown you get from how much known
)
7. Convert from moles of unknown to mass of unknown by multiplying by the GFW of the unknown.
Example
If you decompose (using electricity) 10.0 grams of water, how many grams of oxygen will result?
2H2O --> 2H2 + O2 (Steps 1 and 2: Formulas and balanced equation)
Now set up a factor label problem
| Step 3 | Step 4&5 | Step 6 | Step 7 |
| 10 g H2O | 1mol H2O | 1 mol O2 | 32 g O2 |
| 18.02 g H2O | 2 mol H2O | 1 mol O2 |
= 8.88 g O2
Note: The GFW of Oxygen is 32 g not 16 grams. Why?...... Because good ole oxygen is a wimp (diatomic molecule) O2. Each molecule is two atoms joined, so 32 grams.