The Mole
Q: how long would it take to spend a mole of $1 coins if
they were being spent at a rate of 1 billion per second?
Essential questions
How is a mole used to indirectly count the number
of particles of matter?
2. What is a common everyday counting unit which
the mole can be related?
3. How can moles be converted to number of particles
and vice versa?
1.
MAIN IDEA: Chemists use the mole to count atoms,
molecules, ions and formula units.
The Mole
 The mole is the SI unit for amount of a
substance.
 Definition 1 : A mole is the amount of a
substance that contains as many
particles as there are in exactly 12
grams of carbon-12.
A Mole
 Definition 2 : The amount of a
substance that contains Avogadro’s
number of particles.
Counting Particles
 Dozen = 12
 Ream = 500 sheets
 Pair = 2
 Units for counting, each are appropriate for certain
types of objects.
 Mole = 6.0221367 x 1023 representative particles
Avogadro’s Number
The mole is also known as Avogadro’s
number
Named after Amedeo Avogadro – Italian
physicist and lawyer
In 1811 determined the volume of 1 mol of
gas
For most purposes we will round it to 6.02 x 1023
 Remember how to do scientific notation!?
How big is a mole?
 Avogadro's number of inches is 1,616,434 light
years, or across our galaxy and back 8 times.
 Avogadro's number of seconds is about 19
quadrillion years, 4,240,666
 Avogadro's number of cents could repay the
United States National Debt 86 million times.
 Avogadro's number of kilograms is just over 20
times the mass of the earth.
6.02x1023 PEEPS
6.02x1023 PEEPS
The pile of PEEPS
would cover the US…
6.02x1023 PEEPS
and be as tall as
Mt. Everest.
6.02x1023 dollar bills
6.02x1023 dollar bills
You would spend
$1,000,000,000/sec
6.02x1023 dollar bills
spend $1,000,000,000/sec
19 million years to spend
6.02x1023 pieces of paper
6.02x1023 pieces of paper
would
form a
stack tall
enough
6.02x1023 pieces of paper
to
extend
from the
sun to
Pluto
6.02x1023 pieces of paper
to
extend
from the
sun to
Pluto
Moles of substances
*Now that you understand just how large a mol is, let’s
understand how small atoms are!
1 mol of copper atoms has a mass of 63.546 g
1 mole of carbon atoms has a mass of 12.007 g
1 mole of water molecules has a mass 18.02 g and is
1 mole of sugar molecules has a mass of
1 mole of salt has a mass of 58.45 g
If they all have the same number of particles, why are
does 1 mol of each have a different mass?
Calculating # of particles
 Just like the word dozen, means you have 12 of
something.
 A mole means you have 6.022 x 1023 of something.
 If you have 2 dozen eggs, you have 2 x 12 eggs
 If you have 2 moles of eggs you have 2 x 6.022 x 1023
eggs
Calculating the # of particles
 If you have 0.5 dozen eggs, you have
0.5 dozen x 12 eggs = 6 eggs
1 dozen
 If you have 0.5 mol of carbon, how many carbon
atoms are there?
0.5 mol of carbon x 6.022 x 1023 C atoms = 3.0 x 1023 atoms
1 mol of carbon
Used as Conversion factor
 1 mole/ 6.022 x 1023 particles
 6.022 x 1023 particles / 1 mole
Practice converting:
How many moles of lead, Pb are in 1.50 x 1012 atoms?
Get in HABIT of showing work!(write out conversions)
Answer 2.49 x 10-12 mol Pb
More practice
Solve the following:
How many atoms of zinc are in 7.48 mols of zn?
Calculate the number of molecules of H2O in 11.5 moles
of H2 O
How many moles contain 5.75 x 1024 atoms of Al?
For examples and help see pages 320-324 in textbook.
Day 2
Mass and the Mole
Essential Questions:
Why can the mass of an atom be related to the
mass of a mole of atoms?
2. How can the number of moles be converted to the
mass of an element?
1.
Day 2
Essential Questions:
Why can the mass of an atom be related to the
mass of a mole of atoms?
2. How can the number of moles be converted to the
mass of an element?
1.
MAIN IDEA: A mole always contains the same
number of particles, however, moles of different
substances have different masses.
Relative Atomic Masses
 To set up a relative scale of atomic mass, one atom
was chosen and assigned a mass value. (Carbon-12)
 The mass of all other atoms are expressed in relation
to this one.
 One Atomic Mass Unit – or AMU is exactly 1/12 of the
mass of the Carbon-12 atom
Atomic Mass Units
 The carbon-12 atom has been assigned 12 AMU’s
 Therefore in relation - Hydrogen is approximately
1 AMU
 Activity – Find how many amu’s are the following.
1. Iron
2. Chlorine
3. Magnesium
4. Why aren’t they whole numbers? Well……
Review
 What 3 parts is an atom made of?
Proton – positive - in nucleus
2. Neutron – neutral – in nucleus
3. Electron - negative - outside of nucleus and much
smaller than protons and neutrons.
1.
Average Atomic Masses of Elements
 In nature, elements occur as a mixture of isotopes.
 Isotopes are the same element with a different
number of neutrons so the mass is different.
 The percentage of each isotope is always the same,
no matter where it is found.
 Average Atomic Mass is the weighted average of the
atomic masses of the naturally occurring isotopes of
an element. This is what is on the periodic table.
Example – Carbon
 There are 3 naturally occurring isotopes of carbon:
12, 13, and 14. 12C and 13C are stable, occurring in a
natural proportion of approximately 99:1.
Molar Mass
 The mass in grams of 1 mole of a pure
substance is called the molar mass.
 The molar mass of an element is = to
the atomic mass of the element in
atomic mass units (found on the
periodic table) – but has the units
g/mol
Molar Mass
 Molar Mass is written in units of g/mol
 Molar mass can be used as a
conversion factor to convert from moles
to mass (grams) and back.
Using Molar Mass
 Suppose while working in the lab you need
3.00 mol of copper for a reaction. How
would you measure that amount?
The molar mass of Cu is 63.545g/mol from
the periodic table.
So set up a conversion!
The answer is 191g.
 How are the terms “molar mass” and “atomic mass”




different from one another?
Molar mass is used to describe the mass of one mole
of a compound or element.
Atomic mass is used to describe the mass of one
atom of an element in AMU’s
But they are the same numerically.
NOTE : one atom cannot be weighed in grams! It is
too small!
MORE PRACTICE! Show your work
 What is the mass in grams of 3.57 mol
of Al?
 How many moles is 525 g of Ca?
 Determine the mass in grams from 5.50
x 1022 atoms of He.