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The Mole
REVIEW OF TERMINOLOGY
Atomic mass mass of 1 atom in
AMUs read from P.T.
Atomic Mass
C = 12.011 AMU
H = 1.0079 AMU
Formula units represents a number
of particles whether they are atoms,
molecules or whole ionic compounds.
Coefficients in a chemical reaction
represent formula units
E.g.
2 H2 + 1 C  1 CH4
Formula mass is mass in
AMUs for one formula unit
of a compound.
Formula Mass of
CH4 = 16.05 AMUs
However the AMU is not
practical because it is TOO
small.
Also, how do we relate
AMUs to units we are familiar
with like grams, pounds,
liters, etc..
The MOLE
A little history related to the
development of the mole
While trying to find
Chemical Formulas…
Chemists Discovered a way
of determining
Atomic Masses & the Mole
Chemists discovered that as long
as temperature and pressure is
kept constant gas rxns had whole
number ratio coefficients
2L
1L
Hydrogen
Nitrogen
+1L
+3L
Oxygen
Hydrogen
 Steam
 Ammonia
This helped determine chemical
formulas as follows
2L
Hydrogen
+1L
Oxygen
 Water
So Water is H2O1
1L
Nitrogen
+3L
Hydrogen
 Ammonia
So Ammonia is N1H3
Avogadro realized that to find
formulas from the volumes of
gases used in a chemical reaction
you have to assume equal volumes
of gasses contain the same
number of gas particles
H2
O2
Cl2
In other words, 1 L of
any gas has the same
number of gas particles
no matter what the
composition of the gas.
That allowed
chemists to find
relative atomic
masses
Chemists took equal
volumes of gases &
weighed them to get the
relative atomic masses &
created a new unit called
Atomic Mass Unit (AMU).
So, relative atomic
masses were developed:
E.g. If Nitrogen weighs
14 times as much
as Hydrogen.
1 atom Nitrogen = 14 amu
1 atom Hydrogen = 1 amu
This is where the MOLE
is created
Chemists realized that they could
keep the already established
relative atomic masses, but could
change the unit to grams if they
had enough volume.
All that was needed was to find the
volume to that would match the
atomic masses measured in grams.
What they found is that
22.4 L of a gas will allow you to
keep the numerical value of the
atomic weight, but change the
unit to grams.
22.4 L He = 4 grams He
The Mole is Born
22.4 L which was termed a MOLE is
the amount of gas to make the AMUs
convert directly to grams
22.4 L N2 = 1 mole N2 = 28 g N2
22.4 L only works at S.T.P.
Standard Temp and Pressure
STP is 25 °C and 1 atmosphere
22.4 L H2 @ STP = 1 mole H2 = 2.01 g H2
22.4 L N2 @ STP = 1 mole N2 = 28.0 g N2
22.4 L O2 @ STP = 1 mole O2 = 32.0 g O2
22.4 L CO2 @ STP = 1 mole CO2 = 44.0 g CO2
22.4 L Cl2 @ STP = 1 mole Cl2 = 71.0 g Cl2
Mole
means
Molecular Equivalent
NOTE!!: Mole is standing for a
certain number of particles
(atoms, molecules, formula units).
Chemists just did not know how
many particles yet.
Through Mathematics
& later confirmed by
experimentation we
found that ...
A mole is 6.022 x 10
something.
23
of
It is a name for a number and
the number of gas particles in
22.4 L of a gas!!!!
6.022 x
is called
23
10
(NA)
Avogadro’s Number
DO
WS – Molar Mass
Lab – Molar Mass Methane
Mole Conversions
The Mole is essential to
chemical manufacturing
because the mole links the
atomic scale to the human
scale
atoms & molecules
mass & volume
1 mol of a “X” is
equal to …..
22.4 L X = 1 mol X
23
= __ g X = 6.02 x 10 X
You own a New Neon sign store
and are making a sign that will
take 0.50 L of Ne. You call a gas
supplying store and Ne costs $100
for 100 g. The glass and electrical
equipment cost $30. You charged
$200 for the sign. Did you make or
lose money on the sign?
So Again a Mole is …….
1 mol __ = 6.02 x 1023__ = __ g__
and if it’s a gas the
1 mol ___ = 22.4 L of _____ @ STP
Helpful
reference
chart
Molecules
F.U.s
Atoms
1 mole
6.02 x 1023
6.02 x 1023
1 mole
1 mole
? grams
Moles
22.4 L
1 mole
Volume
(Liters)
1 mole
22.4 L
Mass
(grams)
? grams
1 mole
Conversion
Practice
END