The Mole Concept
The Mole Concept
It is very difficult to deal with individual atoms in
Chemistry because they are way too small, and
reactions occur on the scale of millions of atoms rather
than one or two. Therefore, chemists use the MOLE
when talking about atoms. (The word mole is the
English version of the German word mol, the
shortened form of molekulargewicht meaning
molecular weight)
Using the term mole is similar to the way we use the
term dozen.
The word dozen stands for the number 12.
One dozen eggs is the same as twelve eggs.
The word mole stands for 6.02 X 1023.
In one mole of an element, there are 6.02 X 1023 atoms
of that element.
The Mole Concept
• The formal definition of the mole (abbreviated mol and
given the symbol n) is,
“The amount of substance which contains as many
elementary particles as there are atoms in 12g of carbon12”
• In 12g of carbon-12 there are exactly 6.02 X 1023 atoms of
carbon. This number is known as Avogadro's constant and
is given the symbol NA.
The Mole Concept.
Remember:
MOLE is just a number - it stands for
6.02 X 1023
Celebrating the Mole
• Between 6.02 am and 6.02 pm on the 23rd
October is
What a big number
Avogadro’s number is extraordinarily large – If
it were possible to make a mole of photocopy
paper and pile the paper in a tower, the paper
tower would stretch way past the Sun.
A computer counting 10 billion times every
second would take 2 million years to reach
6.02 X 1023 .
1 mole of marshmallows would cover
Australia to a depth of 900 km.
The Mole Concept.
NA = 6.02 X 1023
Therefore, 1 mole is the same as 6.02 X 1023 particles.
1 mole H2O = 6.02 X 1023 molecules of water
and contains 6.02 X 1023 atoms of oxygen
and 2 x 6.02 X 1023 atoms of hydrogen or 12 x 1023 atoms
of hydrogen or 1.2 x 1024 atoms of hydrogen.
1 mole of Na+ = 6.02 X 1023 ions of sodium
Counting Particles
We can use the formula below to help us count particles:
Number of particles = number of mole x NA
N = n x 6.02 x 1023
This formula can be rearranged to calculate the number of
moles of a substance:
Number of mole (n) = number of particles
Avogadro’s number
Complete the worksheet on
The Mole concept: Counting Particles
Molar Mass (M)
• This is defined as the mass of 1 mol of the element
expressed in grams per mole (g.mol-1)
e.g. Molar mass of Cu atoms = mass of 1 mol of Cu
atoms = 63.5 g.mol-1 (you get this number from the
periodic table)
M(Cu) = 63.5 g.mol-1
Therefore 63.5 g of Cu contains 6.02 x 1023 atoms of
copper.
• What is the molar mass of Fe atoms?
• How many mole are there in 20.0g of calcium
atoms?
Molar Mass
The molar mass of compounds can be found from the periodic table
e.g. M(H2O) = 2 x 1.0 + 16
= 18.0
Therefore M(H2O) = 18 g.mol-1.
What is the molar mass of CaCO3?
What is the molar mass of glucose C6H12O6?
Moles and Mass .
Divide by molar mass
Mass
n=m
M
Multiply by molar mass.
Moles
where n = number of mol
m = mass
M = molar
For example
Determine the number of mole present in 32.0 g of
oxygen atoms
From the periodic table M(O) = 16.0g
Therefore n(O) = 32.0
16.0
= 2.0 mol
Moles and Mass .
Divide by molar mass
Mass
n=m
M
Number of
particles
Moles
Multiply by molar mass.
where n = number of mol
m = mass
M = molar
Divide by 6.02 x 1023
Multiply by 6.02 x 1023
Moles