1. Mole Calculations 1

2. Chemical Calculations
Atoms and molecules are extremely small.
If they are so small and so light, how can we weigh them?
We weigh large numbers of them.

3. Avogadro took 1.00 g of the smallest atom (H) and determined how
many H atoms there are in 1.00 g of H.
He found that:
1.00 g H = x 1023 atoms = mole
This is called Avogadro’s number

4. 1 dozen donuts = 12 donuts
1 century = 100 years
1 millennium = years
1.00 mole = x 1023 particles

5. The mole is a large number of particles
Atom element Cu x 1023 at
1 mole
Molecule covalent CH x 1023 molecules
Formula Unit ionic NaCl x 1023 FUs

6. 1. Convert 2.5 x at C to moles
2.5 x at
x 1 mole
= 42 moles C
x at

7. 2. Convert 16.3 moles CO2 to molecules
x x molecules
= x molecules
1mole

8. 3. Convert 8.9 x 1024 molecules CO2 to moles
= moles CO2
x molecules

9. 4. Convert 28 moles NaCl to Formula Units
x x FU
= x FUs
1mole

10. Determining Avogadro’s Number

11. Electrolysis Apparatus
Ampmeter
Power Supply
Stop Watch

12. Determining Avogadro’s Number
Produce a volume of hydrogen gas while measuring the time and electrical current.
Volume of H mL
Time s
Current amp

13. Background information
1 amp is defined as the number of coulombs per second.
There are x electrons in a coulomb.
The density of H2 is g/L.
It takes 1 electron to make 1 H atom

14. 1. Calculate the number of atoms of H, starting with the time.
x coul
x x el
x 1 at H
= x at s
1 coul
1 el

15. 2. Calculate the number of grams H starting with the volume of H.
10.0 mL
x 1 L
x g
= x g H
1000 mL
1 L

16. 3. Divide the atoms of H by the grams of H to get the number of H
Divide the atoms of H by the grams of H to get the number of H atoms in a gram which is Avogadro’s number.
x at
7.871 x g H
= x at/ 1 gram H
= 5.84 x at/ 1 mole
Avogadro Facts
The Mole Song