Marc Daniels
Chemistry 591
Chemistry Lesson Plan (45-50 minutes):
The Mole and Molar Mass
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Goals: (5 minutes)
To understand the differences between a mole and an atom
To calculate the number of atoms in a given sample
To calculate molar mass and the number of molecules/moles
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Introduction: (10-15 minutes)
A mole or mol is defined as the number equal to the number of carbon atoms in exactly 12
grams
of pure 12C.
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This number is Avogadro’s number where one mole is equal to 6.022 x 1023 units.
1 mole = 6.022 x 1023 units
(One mole of something will consist of 6.022 x 10 23 units of that substance)
1 mole of Substance = 6.022 x 1023 atoms of that Substance
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Molar Mass refers to the mass in grams of one mole of molecules or formula units of
substance.
(The Molar Mass can be found on the periodic table)
For Example Carbon has a Molar Mass of 12.01 grams. This is the mass of one mole of
Carbon, or the mass of 6.022 x 1023 atoms of Carbon.
Mathematically this can be represented as:
(12.01 g C) X (1 mole C/12.01 g C) = 1 mole C
leaving
moles)
(here the grams g cancel out,
(1 mole C) X (6.022 x 1023 atoms C/ 1 mole C) = 6.022 x 1023 atoms C
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Example problems (10-15 minutes)
MOLAR MASS QUESTIONS AND USE OF THE PERIODIC TABLE
What is the mass of 1 mole of Oxygen (O)?
(An exercise to get students used to using the periodic table)
A mole of Oxygen has a mass of 16.00 grams
Other questions of similar form, asking how many grams are in one mole of N, and one mole of B
(14.01g, and 10.81g)
CALCULATING MOLES AND ATOMS
How many moles are in 6.0 grams of carbon?
We know that 1 mole C = 12.01 g C or we can set it as a ration that suggests for every mole of C we have
12.01 grams of C (1 mole C/12.01 g C)
(? Mole C/ 6.0g C) = (1 mole C/ 12.01g C)
(Asks what step do we take next to solve for moles of C?)
? Mole C = (6.0 g C) X (1 mole C/ 12.01g C) = .49 mole C = .5 mole C
We can take this a step further and ask how many atoms of C are there in .5 mole of C?
(? Atoms C/ .5 mole C) = (6.022 x 10 23 atoms C/ 1 mole C)
(Asks what step do we take next to solve for atoms of C? similar process to before)
? Atoms C = (.5 mole C) X (6.022 x 10 23 atoms C/ 1 mole C) = 3.011 x 1023 atoms C
MOLAR MASS OF CHEMICAL COMPOUNDS (10-15 minutes)
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Notation
The subscript near the element tells the number of moles of that element (if there is no number,
this suggest that there is 1 mole….so Cl suggests 1 mole of Cl where Cl2 suggests 2 moles of Cl or 1 mole
of Cl2)
(For example H4 means there are 4 moles of H, but this means that there is only 1 mole of H4
The number/coefficient in front tells the number of moles of that compound (if there is no number,
this suggests there is 1 mole of that compound)
mole
(For example H2O means there are 1 mole of H2O, but there 1 mole of H2 or 2 moles of H, and 1
of O)
Example Problems to finish off class
How many moles of CH4 are there in 6CH4 ?
(There are 6 moles of CH4)
What is the mass of 1 mole of CO2?
(This contains 1 mole of C, and 1 mole O2 or 2 moles of O)
We know 1 mole of C has a mass of 12.01grams and that 1 mole of O has a mass of 16.00grams
so 2 moles of O has 32.00grams === 1 mole of O2 has a mass of 32.00 grams
We now add the masses
12.01grams + 32.00grams = mass of 1 mole of CO2 = 44.01grams CO2
What is the mass of 3 moles of CO2? (3CO2)
We know 1 mole of CO2 has a mass of 44.01grams CO2
So 3 moles of CO2 has a mass of just 3 X (44.01grams CO2) = 132.03 grams of CO2 in 3 moles
of CO2
Time for questions 5-10 minutes