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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
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