Download Molar Mass - Science With Horne

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Moles
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1 mole of a substance contains
6.022 x 1023 particles
Avogadro’s number = 6.022 x 1023
So a “mole” is a number, very similar to
a dozen.
A dozen = 12
A mole (mol) = 6.022 x 1023
It can be found in your reference
packet on page one
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Meaning of Avogadro’s
Number (The mole)
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The mole (abbreviated mol) is the base unit
for measuring the amount of a substance.
The definition of a mole comes from how
many particles (atoms, in this case) there is
in exactly 12 grams of Carbon-12.
Through many years of experimentation, it
has been confirmed that a mole of any
substance has 6.022*1023 representative
particles
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Molar Mass or Gram Formula
Mass (GFM) or Formula Weight
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Molar Mass = the mass of 1 mole of a
substance in grams (also known as Gram
Formula Weight or Formula Weight)
mass given on periodic table is in amu
Because amu and grams are relative we
can say the masses on the periodic table
are in grams
To find molar mass add all the atomic
masses of the elements in the compound.
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Practice – Find the molar mass of:
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MgCl2
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Ca(OH)2
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C6H12O6
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Moles are the central unit in chemistry.
They allow us to change units between:
Mass
 Number of particles (atoms or
molecules or formula units or
particles)
 Volume

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Moles and Mass
The conversion factor is
1 mol = Molar Mass (or GFM or FW)
Convert 5.0 moles of Sulfur to
grams
32.07 g S
5.0 mol S x
 160 g S
1 mol S
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Sample Problem
To carry out a chemical reaction you
need 3.20 moles of zinc nitrate
Zn(NO3)2. What is the mass of 3.20
moles of Zn(NO3)2?
606 g Zn(NO3)2
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Moles and Particles
The conversion factor is
1 mol = 6.022 x 1023 particles (molecules,
atoms, etc)
Convert 2.0 moles H2O to molecules
6.022 x 10 23 mc H 2O
2.0 mol H 2 O x

1 mol H 2O
1.2 x 1024 mc H2O
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Moles and Liters of Gas
The conversion factor is 1 mol = 22.4 L
It only applies to Gas at STP
(standard temperature and pressure)
which is 0 degrees C and 1 atm
Convert 4.3 mol of O2 gas at STP to liters
22.4 L O 2
4.3 mol O 2 x
 96 L O 2
1 mol O 2
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Sample Problem
A piece of marble contains 8.74 x 1023
formula units of calcium carbonate.
How many moles of CaCO3 is that?
1.45 mol CaCO3
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Hall Analogy
Liters (of Gas
At STP) 1 mole = 22.4 L
Mass
1 mole = GFM
M
O
L
E
S
Molecules
1 mole = 6.022 x 1023 particles
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Traffic Circle Analogy
To get to volume,
mass, or particles,
you have to pass
through the mole!
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Sample Problem
You need 250 grams of table sugar, or sucrose
(C12H22O11), to bake a cake. How many
sucrose molecules will be in the cake?
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1 mol 6.022 x 10 mc
250 g x
x

342.3 g
1 mol
4.4 x 1023 molecules C12H22O11
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Sample Problem
If you burned 4.00 x 1023 molecules of
natural gas, or methane (CH4) during a
laboratory experiment, what mass of
methane did you burn?
10.7 g CH4
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