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

= 42 moles C6.02 x 1023 at

x 1 mole2.5 x 1025 at

2. Convert 16.3 moles CO2 to molecules

= 9.81 x 1024 molecules1mole

x 6.02 x 1023 molecules16.3 moles

3. Convert 8.9 x 1024 molecules CO2 to moles

= 15 moles CO26.02 x 1023 molecules

x 1 mole8.9 x 1024 molecules

= 1.7 x 1025 FUs1mole

x 6.02 x 1023 FU28 moles

4. Convert 28 moles NaCl to Formula Units

Determining Avogadro’s Number

Ampmeter

Power Supply

Stop Watch

Electrolysis Apparatus

Determining Avogadro’s Number

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

Volume of H2 10.0 mLTime 80.7 sCurrent 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 0.07871 g/L.

It takes 1 electron to make 1 H atom

1. Calculate the number of atoms of H, starting with the time.

= 4.5976 x 1020 at1 el

x 1 at H1 couls

x 6.24 x 1018 elx 0.913 coul80.7 s

2. Calculate the number of grams H starting with the volume of H.

= 7.871 x 10-4 g H1 Lx 0.07871 g

1000 mLx 1 L 10.0 mL

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.

7.871 x 10-4 g H

= 5.84 x 1023 at/ 1 gram H

= 5.84 x 1023 at/ 1 mole

The Mole Song

4.5976 x 1020 at

Avogadro Facts