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Honors Chemistry
The Mole & Avogadro’s Number Notes
Name ______________________________
Period ____
Measuring Matter
Substances react according to definite ratios of numbers of particles (atoms, ions, formula units, or molecules). The
following balanced chemical equation shows that two atoms of aluminum react with three molecules of iodine to
form two formula units of aluminum iodide.
2Al(s) + 3I2(s)  2AlI3(s)
If you wanted to carry out this reaction, how could you measure the correct numbers of particles of aluminum and
iodine? Fortunately, you can count particles by measuring mass. Suppose you have a sample of an element, and the
mass of the sample in grams is numerically equal to the atomic mass of the element. Scientists have discovered that
this mass of an element contains 6.02 x 1023 atoms of that element. This number is called Avogadro’s number.
Avogadro’s number of particles is called a mole of particles. The mole is the SI base unit used to measure the
amount of a substance and is defined as the number of particles in exactly 12 g of pure carbon-12. For the purpose
of dealing with moles, the simplest unit of any substance is called a representative particle. The particle may be an
atom, a molecule, a formula unit, or an ion.
Example Problem 1: Converting Moles to Number of Particles
How many molecules are in 2.25 moles of bromine?
Bromine is an element that consists of diatomic molecules. Therefore, one mole of bromine contains 6.02 x 10 23 Br2
molecules. To find the number of Br2 molecules present in 2.25 mol, multiply the number of moles by Avogadro’s
number.
number of Br2 molecules =
2.25 mol x 6.02 x 1023 molecules Br2
1 mol
number of Br2 molecules = 1.35 x 1024 molecules Br2
Example Problem 2: Converting Particles to Moles
Calculate the number of moles in a sample of sodium bromide that contains 2.88 x 1023 formula units.
Because 1 mol NaBr = 6.02 x 1023 formula units NaBr, you can see that 2.88 x 1023 formula units is less than one mole
of NaBr.
moles of NaBr =
2.88 x 1023 formula units x
1 mol NaBr
6.02 x 1023 formula units
moles of NaBr = 0.478 mol NaBr
The Mole & Avogadro’s Number Notes
Additional Notes/Examples
Notetaking
Counting Units:
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Measuring a Mole - Counting Atoms (Molecules):
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How big is a mole?
 One mole of popcorn:
 One mole of stacked pennies:
 One mole of marshmallows:
History of Avogadro’s Number
 Avogadro – 1811:
 Cannizzaro – 1861:
 Ostwald – 1902:
 1971:
The Law of Conservation of Mass
 According to the Law of Conservation of Mass,
Mass of reactants = mass of products
Mass of starting substances = mass of ending substances
 So the production of one water molecule requires:
Therefore,

And
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The Law of Definite Proportions and Ratios of Atoms
 Law of Definite Proportions:
 Example:
Moles  Particles Conversions:
Examples Conversions:
1) 3.5 moles to atoms
2)
18.06 x 1023 atoms to moles
Convert from moles to particles:
3)
2.7 moles to particles
4)
4.32 x 1024 atoms to moles
5)
5.3 moles of bromine
6)
4.7 moles of potassium oxide
Convert from particles to moles:
7) 4.32 x 1024 atoms of calcium
8) 2.7 x 1020 atoms of copper
9) 2.5 x 1024 molecules of sodium chloride
10) 5.32 x 1023 molecules of calcium chloride
You try these:
10) 25 moles to particles
11) 4.08 x 104 particles to moles
12) 0.002 moles to particles
13) 2.3 x 1016 particles
Practice Problems:
1. Calculate the number of molecules in 15.7 mol carbon dioxide.
2. Calculate the number of molecules in 0.0544 mol H2O.
3. Calculate the number of moles in 9.22 x 1023 atom iron.
4. Calculate the number of moles of sucrose in a sample that contains 2.05 x 1022 sucrose molecules.
5. A student uses 0.0850 mol copper sulfate to carry out a reaction. If the reaction uses up 0.0832 mol copper
sulfate, how many formula units are left unreacted?
Honors CHEMISTRY
Moles  Particles Conversions WS I
Use the factor label method to convert the following on your own sheet of paper. Circle your answers.
Moles to Particles:
Particles to Moles:
1.
1.8 moles to particles
1.
2.7 x 1020 atoms to moles
2.
5.3 moles to atoms
2.
2.5 x 1024 molecules to moles
3.
4.7 moles to atoms
3.
5.32 x 1023 atoms to moles
4.
25 moles to molecules
4.
4.08 x 1014 particles to moles
5.
0.0018 moles to atoms
5.
2.3 x 1016 atoms to moles
Honors CHEMISTRY
Moles  Particles Conversions II WS
Use the factor label method to convert the following on your own sheet of paper. Circle your answers.
Moles to Particles:
Particles to Moles:
1.
10.6 moles to particles
1.
6.9 x 1022 atoms to moles
2.
2.4 moles to atoms
2.
7.3 x 1024 molecules to moles
3.
0.75 moles to atoms
3.
4.18 x 1023 atoms to moles
4.
18 moles to molecules
4.
2.5 x 1019 particles to moles
5.
0.039 moles to atoms
5.
1.67 x 1021 atoms to moles