Download The MOLE

The MOLE
? Mole
The mole is a word that means a very specific
number. We know about the word “dozen” it
means 12 items.
The mole means 6.0221367 x 1023 particles.
we just round it to 6.022 x 1023.
If we have a mole of anything we have 6.022 x 1023 of them.
That’s a lot of anything to have, unless you think about atoms
and molecules.
1 mole of particles =
602,213,670,000,000,000,000,000 particles
The number
has made me
crazy.
Avogadro’s number
Avogadro's number and is denoted by NA. It is derived
from exactly 12 grams of carbon-12. 12 grams of
carbon-12 has approximately 6.02 x 1023 atoms.
Amadeo Avogadro
(1776-1856)
What do we do with it?
It happens to be the SI unit of amount of anything.
We use it in chemistry when working with chemical
equations.
It can stand for: atoms, molecules, or formula units.
The mass of a mole of any one element is equal to
its atomic mass.
So…
1 mole “C” = 6.02 x 1023 “C” atoms = 12.01 grams
Carbon
1 mole C
1 mole C
6.02 x 1023 atoms
12.01 g
6.02 x 1023 atoms
12.01 g
All of these can be filled around to make 3
more conversion factors, for a total of 6.
What is the mass of 2.5 moles of aluminum?
We look on the Periodic table to find the atomic mass of Al.
This tells us that 1 mole of Al = 26.98 grams.
Time for math:
2.5 moles Al x 26.98 g = 67.45 g of Al
1 mole of Al
The Key
For an example lets use gold (Au).
[1 mole of Au = 6.02 x 1023 atoms of Au = 196.97 grams of Au]
These three numbers are all we need to solve any
molar equations dealing with gold.
Examples:
1. What is the mass of 4.5 moles of Au?
2. How many atoms of Au will have a mass of 89.60g?
3. How many moles of gold do you have if you have 5.24 x 1026
atoms of gold?
4. What will be the mass of 5.24 x1026 atoms of Gold?
What is the mass of 4.5 moles of Au?
4.5 mol Au x 196.97 g = 886.36 g Au
1 mol Au
1 mole of Au = 6.02 x 1023 atoms of Au = 196.97 grams of Au
How many atoms of Au will have a mass of 89.60g?
89.60g Au X 6.02x1023 Au atoms = 2.738 x1023 atoms Au
196.97 Au
You are going to
need one of
these!
1 mole of Au = 6.02 x 1023 atoms of Au = 196.97 grams of Au
Molar mass of an ionic compound
&
Molar mass of a molecular compound
We have reviewed the mole concept for a
single element (gram atomic mass or gam).
Example:
Na: 1mole = 22.99g
or we could put it like this
22.99g Na/1 mole Na
Mole of a compound: Ionic & molecular
Consider NaCl
Na has a molar mass of 22.99 g/mol
Cl has a molar mass of 35.45 g/mol
So what is the molar
mass of NaCl?
22.99
+
35.45
58.44 g/mol
We would say that the gfm (gram formula mass) of
NaCl is 58.44g/mol
gfm is the same thing as molar mass, but it goes with
ionic compounds.
More examples:
One way to determine the molar mass is like this:
Fe2O3 Iron (III) oxide
Element
# of atoms
Grams /mol
Total mass of
that element
Fe
2
X
55.47
=
110.94
O
3
X
16.00
=
+ 48.00
Total
158.94 g/mol
More examples:
Zn(OH)2
Zn
1
65.39
65.39
“Zinc hydroxide”
O
2
16.00
32.00
H
2
1.00
+
2.00
99.39
The gfm or molar mass of zinc hydroxide is 99.39g/mol
What about molecular
compounds
Its really the same way!
You calculate it.
How about water (H2O)?
Element
# of
atoms
Grams
/mol
Total mass
of that
element
H
2
X
1.00
=
O
1
X
16.00
=
Total
2.00
+ 16.00
18.00 g/mol
Conversion factors
1 mole H2O = 18.00 grams = 6.02 x 1023 molecules of H2O
1 mole H2O
18.00 g H2O
18.00 g H2O
18.00g H2O
1 mole
6.02 x 1023 molecules
Q. What is the mass of 2.5 moles of water?
2.5 moles of H2O x 18.00 g H2O = 45.00g H2O
1 mole H2O
Mass to moles
How many moles of silver nitrate (AgNO3) will have a mass of
55.0g?
1st find gfm of AgNO3
Ag 1 x 107.87 = 107.87
N 1 x 14.01 = 14.01
O 3 x 16.00 = + 48.00
169.88 g/mol
55.0g AgNO3 x 1 mole AgNO3 = 0.324 mole AgNO3
169.88 g AgNO3
Page 340 in chemistry text.