Transcript Moles

The Mole
How people see chemistry
experimentally is different
than how they see it
theoretically.
Theoretically we use
atoms and molecules
Experimentally we use
mass and volume
How did we
solve this
problem?
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 followed
whole number ratios
2L
Hydrogen
1L
+1L
Nitrogen
Oxygen
+3L
 1 L Steam
Hydrogen
Ammonia
1L
This helped determine chemical
formulas as follows
2L
Hydrogen
+1L
Oxygen
 1 L Water
Then Water is 1 H2O1
1L
Nitrogen
Ammonia
+3L
Hydrogen
1L
Then Ammonia is 1 N1H3
To find formulas this way,
Avogadro realized that you have to
assume that the number of gas
particles determines volume not how
massive the particles are
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 and
weighed them to get
the relative atomic
masses in AMUs.
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 change the unit to
grams if they had enough
volume. All they had to do is
find that volume.
What they found is that
22.4 L of a gas will allow you
to keep the numerical value
of the atomic weight, but the
unit is now in grams.
22.4 L He = 4 grams He
The Mole
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
NOTE: Mole is standing for a
certain number of particles
(atoms, molecules, etc).
Chemists just did not know
how many particles yet.
At this point chemists
Could find the formulas of compounds
made from gases
Had a way to measure atomic masses
of anything that was a gas
Had a way to relate Masses and
Volumes to a Relative Number of
Particles
DO
WS – Formula & Molar Mass
Lab – Molar Mass Methane
The Mole is essential to
chemical manufacturing
because the mole links the
atomic scale to the human
scale
atoms & molecules
mass & volume
REVIEW OF MASS
RELATED TERMINOLOGY
Atomic mass mass of 1 atom in
AMUs read from P.T.
Atomic Mass
C = 12.011 AMU
H = 1.0079 AMU
Formula mass is mass in
AMUs for one formula unit
of a compound.
Formula Mass of
CH4 = 16.05 AMUs
Formula units represent the 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
A molar mass is the
mass in grams of
Avogadro’s # of the
substance or 22.4 L
of gas at S.T.P..
A mole is a more
practical amount
for use in
experiments and
industry
Atomic mass of C = 12.011 amu
Molar mass of C = 12.011 g
Formula mass of CO2 = 44 amu
Molar mass of CO2 = 44 g
How many particles are in a
mole (also known as 22.4 L of
a gas at STP or the molar
mass of a substance)?
Through Pure
Mathematics and later
confirmed by expensive
equipment we
found………….
1 Mole ____ = 6.022 x 1023 ____
1 Mole C = 6.022 x 1023 atoms C
1 Mole NH3 = 6.022 x 1023 formula units NH3
1 Mole KCl = 6.022 x 1023 formula units KCl
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
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
Practice
Worksheets
You own a New Neon sign store
and are making a sign that will
take 0.5 L of Ne. You call a gas
supplying store and Ne costs $100
for 100 g. You charged $200 for the
sign. The glass and electrical
equipment cost $30. Did you make
or lose money on the sign?
Review Problems:
Using Mole,
Volume, Mass and
Formula Units
END