Molar Mass - PowerPoint

							Mole Calculations 1
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.
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 = 6.02 x 1023 atoms = 1.00 mole

This is called Avogadro’s number
1 dozen donuts = 12 donuts

1 century       = 100 years

1 millennium      = 1000 years

1.00 mole      = 6.02 x 1023 particles
The mole is a large number of particles

Particle

Atom                 element        Cu     6.02 x 1023 at
                                            1 mole

Molecule             covalent       CH4    6.02 x 1023 molecules
                                            1 mole

Formula Unit         ionic          NaCl   6.02 x 1023 FUs
                                           1 mole
1. Convert 2.5 x 1025 at C to moles


2.5 x 1025 at C x      1 mole             =   42 moles C
                       6.02 x 1023 at C
2. Convert 16.3 moles CO2 to molecules



16.3 moles   x    6.02 x 1023 molecules   = 9.81 x 1024 molecules
                               1mole
3. Convert 8.9 x 1024 molecules CO2 to moles



8.9 x 1024 molecules   x   1 mole                =   15 moles CO2
                           6.02 x 1023 molecules
4. Convert 28 moles NaCl to Formula Units


28 moles   x   6.02 x 1023 FU     = 1.7 x 1025 FUs
                   1mole
Determining Avogadro’s Number
Ampmeter                    Electrolysis Apparatus




             Power Supply


Stop Watch
Determining Avogadro’s Number

Produce a volume of hydrogen gas while measuring the time and
electrical current.

Volume of H2                       10.0 mL
Time                               80.7 s
Current                            0.913 amp
Background information

1 amp is defined as the number of coulombs per second.

There are 6.24 x 1018 electrons in a coulomb.

The density of H2 is 0.08428 g/L.

It takes 1 electron to make 1 H atom
1. Calculate the number of atoms of H, starting with the time.



80.7 s x 0.913 coul x 6.24 x 1018 el   x 1 at H   = 4.5976 x 1020 at
               s         1 coul          1 el
2. Calculate the number of grams H starting with the volume of H.


10.0 mL x      1L      x     0.08428 g
            1000 mL            1L         = 8.428 x 10-4 g H
3.   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.

              4.5976 x 1020 at
              8.428 x 10-4 g H

               =       5.45 x 1023 at/ 1 gram H

               =       5.45 x 1023 at/ 1 mole

                                     Avogadro Facts
           The Mole Song