The Mole
The following provides an overview of
moles and the skills necessary for
performing mole conversions
Definition of a Mole
A dozen is a number that has been given a
name. The same can be said for a mole. The
only difference is that the number defined as
a mole is very, very, very, very, very, very,
very ,very, very, very, very, very, very, very,
very, very, very, big!!!
1 mole = 6.02 x 1023
(602,000,000,000,000,000,000,000)
Avogadro’s Number
Is A Mole Really That Big?
If an atom were the
size of a marble and
one mole of marbles
were spread over
the surface of the
Earth, our planet
would be covered by
a 50 mi-thick layer.
Is A Mole Really That Big?
A new supercomputer
can count all of the
people in the United
States in one-quarter
of a second, but it
would take almost two
million years for it to
count one mole of
people at the same
rate.
Is A Mole Really That Big?
If you made
$40,000 (4,000,000
pennies) every
second at your job
that you had been
working at since the
formation of earth
4.5 billion years ago,
you would not yet
have earned
Avogadro’s number
of pennies.
So How is a Mole Helpful?
Scientists obviously can’t mass quantities of
chemicals in amu because an amu is far too
small. When scientists work with a substance
like H2O, they can’t deal with single molecules
– we can’t see or mass 2 atoms of hydrogen
and one atom of oxygen. Scientists obviously
have to work with much larger quantities. To
solve this problem, scientists use the mole.
To be useful the mole has to be somehow
related to amu. Officially, the mole (symbol
mol) is the SI term for the amount of
substance containing as many elementary
particles as there are atoms in 0.012 kg of
carbon-12 (which is about 6.02 x 1023atoms)
Where do you find how much a
mole of something weighs?
The atomic mass given on the periodic table is not
only the mass of one atom of that element, but it is
also the mass (in grams) of 1 mole of the atoms of
that element. Therefore, since the mass of one
carbon atom is 12 amu, the mass of one mole of
Carbon atoms would be 12 grams. When dealing with a
molecule or compound you simply calculate the
molecular/formula mass using the periodic table, and
this (like with atoms) is not only the mass of one
molecule/compound, but it is also the mass (in grams)
of 1 mole of the molecule/compound. Therefore,
since the mass of one molecule of ozone (O3) is 48
amu, the mass of one mole of ozone molecules would
be 48 grams.
How much does it weigh?
You may want to use your periodic table!
1 mole of Oxygen
1 mole of Sodium
2 moles of Carbon
3 moles of Hydrogen
1 mole of H2O
16 grams
23 grams
24 grams
3 grams
18 grams
Mole Map
This map is to help you navigate mole problems
Mass (Grams)
Excuse
me, how
do I get
to Atoms?
Moles
If you use
the map,
you won’t
get lost!!!
Atoms, Molecules,
Particles,
Etc.
Just start at
grams, go
straight
through moles
and you will get
to atoms.
Sample One Step Problem
Calculate the mass of 7.5 moles of Carbon.
Use the “map” to help figure it out
Mass (Grams)
Moles
Atoms, Molecules,
Particles,
Etc.
What is the starting point in this problem?
What is the final destination in this problem?
How many steps/fractions will it take you to get there?
One Step Problem
Calculate the mass of 7.5 moles of Carbon.
7.5 moles of C  grams of C
(7.5 moles of C) (____________)
12 grams of C
(1)
= 90 grams of C
( 1 mole of C)
Explanation
Mass (Grams)
Use Periodic table
Moles
Atoms
Use 1 Mole = 6.02x1023
#6
–Finally,
multiply
across
the
top,
#4
–Since
you
are
aware
that
itat
isthe
#2
#3
#5
#1 –Since
–Place
–Multiply
–Now
that
your
you
between
have
you
starting
have
already
fractions
arrived
point
found
over
and
your
multiply
across
the
bottom,
and
divide
the
necessary
to
travel
to
grams
you
can
one.
make
final
starting
destination
In
sure
this
point,
the
case
bottom
final
(grams)
you
destination,
will
unit
you
beof
placing
can
the
and
simply
new
the
product
of
top
by
the
product
simply
place
that
the
topunit
ofof
the
7.5
fraction
cancel
number
moles
all
of
isother
of
steps
the
carbon
same
diagonal
itunit
will
over
ason
take,
the
units.
one.
top
you
should
ofthe
the
bottom.
This
will
give
you
the
final
answer,
fraction.
To
determine
the
mass
ofunit
a is
previous
now writefraction.
down
a little
In this
reminder
case
the
of
which
incarbon
this
case
90 the
grams
of C. table.
mole
youisuse
periodic
“mole
all ofof
this
of
carbon.”
information.
In this case, one mole of carbon has a
mass of 12 grams. You plug these numbers
into the fraction, letting the units guide
you. You have now transitioned from
moles to grams.
Sample Two Step Problem
How many atoms are in 45.8 grams of Na?
Use the “map” to help figure it out
Mass (Grams)
Moles
Atoms, Molecules,
Particles,
Etc.
What is the starting point in this problem?
What is the final destination in this problem?
How many steps/fractions will it take you to get there?
Two Step Problem
How many atoms are in 45.8 grams of Na?
45.8 grams  atoms of Na
6.02x1023atoms of Na
(45.8 grams of Na) (_____________)
1 mole of Na (________________)
(1)
( 23 grams of Na )
= 1.20 x 1024 atoms of Na
Mass (Grams)
Use Periodic table
Moles
Atoms
Use 1 Mole = 6.02x1023
( 1
mole of Na)
Explanation
#4
–Since
you
are
aware
that
it over
istop,
#2 –Since
–Placethat
your
starting
point
#3
–Multiply
between
fractions
and
#6
#5
#7
#1
–Now
you
are
have
you
at
have
already
moles,
arrived
found
it
is
at
now
the
moles it
your
#8
–Finally,
multiply
across
the
necessary to travel to atoms, according to
one.be
In
this
case
you
will
beof
placing
make
sure
the
bottom
unit
the
new
possible
will
final
starting
destination
necessary
for
point,
you
final
to
(atoms)
to
travel
destination,
continue
you
to
atoms;
can
your
and
simply
travels
the
multiply
across
the
bottom,
and
divide
the
the “Mole Map,” you must stop at moles
45.8
grams
of should
sodium
over
one.
fraction
is
the
same
as
the
top
the
therefore
to
cancel
number
atoms
all
of
since
other
you
steps
moles
diagonal
it by
will
place
isthe
take,
not
units.
that
your
youunit
unit
final
should
on
product
the
top
product
ofof
the
first. Therefore you should place that unit
previous
fraction.
In
this
case
the
unitthe
is
the
destination.
now
top
write
of
down
the
Once
fraction.
afraction.
little
again,
reminder
To
you
determine
need
ofto
bottom.
This
will
give
you
the
final
answer,
on
the
top
of
the
To
determine
24sodium
“grams
sodium.”
number
multiply
all
of
this
between
atoms
fractions
mole of
and
make
you
sure
which
inof
this
is
atoms
of
the
mass
ofinformation.
a case
molein
ofa1.20x10
sodium
you
use
the
23
simply
the
bottom
use
1 unit
mole
= 6.02x10
the
newone
fraction
. mole
You plug
sodium.
periodic
table.
In of
this
case,
ofis the
these
same
numbers
the
topinto
unit
ofgrams.
fraction,
the previous
sodiumas
has
a mass
ofthe
23
Youletting
plug
the
fraction.
units
guide
In
this
you.
case
You
the
have
unit
now
is
“mole
of
these numbers into the fraction, letting the
transitioned
sodium.”
from
to atoms.
units guide you.
Youmoles
have now
transitioned
from grams to moles.
Sample Problem That Requires Some Prep
Work Before Converting
Calculate the mass of two moles of the compound Ca(NO3)2.
What is different about this problem when compared to
the others?
Ca(NO3)2 - it is not an atom
You should calculate
Ca = the
40gmolar
x 1 =mass
40 using
g/molyour periodic
table prior to using
subsequently
N =your
14gmap
x 2and
= 28
g/mol converting
O = 16g x 6 = 96 g/mol
1 mole of Ca(NO3)2 = 164 g
Now that you know the molar mass of Ca(NO3)2
you can use your map and convert
Sample Problem That Requires Some Prep
Work Before Converting
Calculate the mass of two moles of the compound Ca(NO3)2.
Use the “map” to help figure it out
Mass (Grams)
Moles
Atoms, Molecules,
Particles,
Etc.
What is the starting point in this problem?
What is the final destination in this problem?
How many steps/fractions will it take you to get there?
Continuation of Problem After Prep
Work is Complete
Calculate the mass of two moles of the compound Ca(NO3)2.
2 moles of Ca(NO3)2  grams of Ca(NO3)2
1 mole of Ca(NO3)2 = 164 g
164 grams of Ca(NO3)2
(__________________)
(2 moles of
Ca(NO3)2)
( 1 mole of Ca(NO3)2 )
(1)
= 328 grams of Ca(NO3)2
Mass (Grams)
Use Periodic table
Moles
Compounds
Use 1 Mole = 6.02x1023
Explanation
#4
–Since
you
are
aware
that
itat
is
#2
#3
#5
#1 –Since
–Placethat
–Multiply
–Now
your
you
between
have
you
starting
have
already
fractions
arrived
point
done
over
and
some
your
#6
–Finally,
multiply
across
the
top,
necessary
to
travel
todetermined
grams
you
can
one.
make
final
preliminary
destination
In
sure
this
the
work
case
bottom
(grams)
and
you
will
unit
you
beof
placing
can
the
simply
the
new the
multiply
across
the
bottom,
and
divide
simply
that
unit
on
the
topunit
ofof
the
2
fraction
cancel
mass
moles
ofplace
allof
aof
isother
mole
Ca(NO
the
same
of
diagonal
)by
over
the
units.
)one.
found
the
ofthe
the
product
top
the
product
3Ca(NO
2 as
3
2,top
fraction.
To determine
the
mass
ofunit
atheis
previous
starting point,
fraction.
final
In
destination,
this
case
the
and
bottom.
This
will
give
you
the
final
mole
of
)2)this
have
already
used of
“mole
number
ofCa(NO
of
Ca(NO
steps
it
.”will
take,
you should
answer,
which
in
case
is
328
grams
33
2you
your
periodic
table
and reminder
you calculated
now write
a little
of a
Ca(NO
3)2.. down
mass
164
grams. You plug these
all of of
this
information.
numbers into the fraction, letting the
units guide you. You have now transitioned
from moles to grams.