1. Multi-Step Mole Conversions

2. Atoms/Molecules and Grams and Liters
Since 6.02 X 1023 particles = 1 mol
AND mole = molar mass (grams)
AND 1 mole = 22.4 liters (at STP)
You can’t go directly from atoms to grams or from liters to atoms!!!! You MUST go thru MOLES.
That’s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first!

3. Calculations Everything must go through Moles!!! Liters
molar mass Avogadro’s number Grams Moles particles
22.4 L at STP
Liters
Everything must
go through Moles!!!

4. Example #1
How many atoms of Cu are present in 35.4 g of Cu?

5. Example #1 How many atoms of Cu are present in 35.4 g of Cu?
35.4 g Cu mol Cu X 1023 atoms Cu g Cu mol Cu
= 3.35 X 1023 atoms Cu

6. How many atoms of K are present in 78.4 g of K?
Example #2
How many atoms of K are present in 78.4 g of K?

7. Example #2 How many atoms of K are present in 78.4 g of K?
78.4 g K mol K X 1023 atoms K g K mol K
= 1.21 X 1024 atoms K

8. What is the mass (in grams) of 52.5 Liters of Oxygen gas (O2)?
Example #3
What is the mass (in grams) of Liters of Oxygen gas (O2)?

9. Example #3
What is the mass (in grams) of 52.5 Liters of Oxygen gas (O2)?
52.5 L O mol O g O L O mol O2
= 75.0 g O2

10. Practice Problems
What is the mass of 5.26x1027 Iron (III) Hydroxide molecules? Fe(OH)3 for those you who have forgotten how to do cross over & down!
How many liters does 860 grams of nitrogen gas (N2) occupy in a tank?
How many atoms of oxygen are in 4.30 L of CO2?