The mole is used mostly in chemistry as a SI unit for amount of substance.
In simplest terms a mole represents a number of objects.
Suppose you’re engaged in a building project: laying a floor. You’re going to put down 25 boards with 10 nails a piece: that’s at least 250 nails you’ll need. When you go to the hardware store and ask for 250 nails, the clerk doesn’t count out the nails for you. What do they do?

When we need a large number of a small item, it doesn’t make sense to count them out; weighing is more efficient. We probably won’t get exactly the number we want, but if we’re dealing in large numbers it won’t make much difference if there are a few more or less.

In chemistry, we’re stuck with using just this method to count atoms and molecules, because it’s the only way we can do it.
Q: Can we count out atoms one-by-one?
A: No, they are too small, but we do need to know how many we have in a bunch so we can study their behavior, which is what chemistry is all about.
Q: In chemistry labs or when cooking or baking at home, how do we measure out chemicals/reactants/ingredients?
A: We either measure it out per a certain volume amount, such as in a graduated cylinder or in a measuring cup, or we weigh it out, like on a balance.

It is important to know how much of a particular substance we have in order to study its behaviour.
Weighing atoms in order to count atoms is not an exact science. If we were to weigh out 250 nails it would be less accurate than actually counting each nail. However, it is much more practical to weigh the nails.

Because atoms and molecules are so small, chemists created a quantity called a mole that represents a large number of atoms. The unit of a mole is like a dozen in that it represents a certain number of atoms or molecules.
What is a dozen?
What do we call 2 things?

When can we use the terms a dozen or a pair?
We use terms such as dozen or pair in order to represent a particular number of objects.

It is a very, very, very large number but the same idea as a pair, a dozen, a gross, and so on . A pair is 2 items, a dozen is 12 items, a gross is 144 items, and a mole is 6.02 × 10 23 items. That is
602,000,000,000,000,000,000,000 items in a mole. This number is usually expressed in scientific notation.

23

• A long while a go a man by the last name of
Avogadro came up with an idea of how to group atoms! The mole is also referred to as
Avogadro’s number!
• If two elements were at equal volume, temperatures and pressure, he figured there would be the same number of particles in each.

How big is a mole of basketballs?
What is another name for the mole?
Why do we use the mole?
http://ed.ted.com/lessons/daniel-dulek-how-big-is-amole-not-the-animal-the-other-one

Q: can a dozen represent any number besides 12 or can a pair represent a number other than two?
A: No, these numbers are constants, which mean that they always represent the exact same number regardless of the item.
The mole is most specifically used to count atoms.
Even though a mole is like a dozen, the actual number is much larger because atoms are much smaller than the eggs or oranges we usually measure by the dozen.

Suppose you buy three and a half dozen roses and you want to know how many roses you have. You can multiply the known quantity (3.5 dozen) by a conversion factor to express the quantity in the units you want (number of roses).

Conversion factor: 12 roses
1 dozen

NOTE: 1 MOLE = 6.02 X 10 23 PARTICLES
PARTICLES (ATOMS OR MOLECULES)
How many particles of sucrose are in 3.50 moles of sucrose?

Calculate the number of moles that contain 4.50 x 10 24 atoms of zinc.

Example 3: How many molecules are in 4.00 mols of NaCl?
4.00 mols NaCl x 6.02 x 10 23 molecules
1 mol NaCl
= 2.41 x 10 24 molecules NaCl

1.
How is a mole similar to a dozen?
2.
Why do chemists use the mole?
3.
Do the following conversions using dimensional analysis: a) How many atoms in 2.50 mol Zn?
b) How many moles contain 5.75 x 10 24 atom Al?
c) How many moles contain 3.58 x 10 23 formula units
ZnCl ?
2 d) How many formula units given 3.25 mol AgNO
3
?
e) How many molecules in 11.5 mol H
2
O?
f) How many moles contain 3.75 x 10 24 molecules CO
2 g) How many moles contain 2.50 x 10 20 atoms Fe?.
?

http://www.youtube.com/watch?v=1R7NiIum2TI

Avogadro’s number is also used to represent how many atomic mass units can be found in a gram.
This allows us to use the mass numbers on the periodic table for both the mass of an atom
(atomic mass) and the mass of a mole of atoms
(molar mass), we only need to change the units.
What is atomic mass?
Atomic mass is the weighted average mass of the isotopes of that element.
Molar mass – the mass in grams of one mole of any pure substance.

Atomic mass = molar mass amu = g/mol
What is the molar mass of copper?
What is the molar mass of carbon
?

• How can the molar mass of copper and carbon be different if a mole is always 6.02x 102 3 atoms?
• This is the same as asking how the weight of a dozen elephants can be different than the weight of a dozen ants. It is the number of items that is always the same, not the mass of weight or size of those items.

What is the molar mass of H
2
O?
What is the molar mass of Ca(OH)
2
?

a) N
2
O
5 b) H
2
CO
3 c) NaC
2
H
3
O d) CuClO
3 e) Ba(NO
2
) f) Pb(HSO
4
3
2
)
2



Imagine that you are buying jellybeans. Instead of counting out each jellybean they are measured by mass. You find that 1 dozen has a mass of 35 g.
What mass of jellybeans should you measure if you want 5 dozen?
35g jellybeans / 1 dozen

Suppose that while working in a chemistry lab you need 3.00 moles of manganese for a chemical reaction. How can you measure that amount?

How many moles of calcium are in 525 g calcium?

How many moles of NaCl are in 234.0g NaCl?
How many grams would 2 moles of NaCl be?

Determine the mass in grams of each: a) 3.57 mol Al c) 3.45 mol H
2
O b) 42.6 mol Si d) 2.45 mol ZnCl
2
Determine the number of moles in each: a) 25.5 g Ag b) 125g Zn c) 300.0g Na
2
S d) 1.00 kg Fe

Just as we could not make a direct conversion from cm  km we cannot make a direct conversion from mass to atoms. Instead we use two step dimensional analysis.
Mass  Moles  Atoms
Atoms  Moles  Mass

How many atoms are in 25.0 g of gold?

A party balloon contains 5.50 x 10 22 atoms of He gas. What is the mass in grams of the helium?

How many atoms are in each of the following samples?
a) 0.230 g Pb b) 11.5g Hg c) 45.6 g Si d) 0.120kg CaCl
2
What is the mass in grams of each of the following: a) 1.00 x 10 24 atoms Mn b) 3.40 x 10 22 atoms He c) 1.50 x 10 15 atoms LiCl d) 1.50 x 10 15 atoms U

Hand – In Questions:
1.
How many atoms are in 55.2 g Li?
2.
What is the mass of 6.02 x 10 24 atom Bi?
3.
How many molecules are in 0.000349g of calcium iodide?
4.
What is the mass of 3.34 x 10 22 molecules H
2
O?
5.
How many sodium chloride atoms in 117g of NaCl?

Determining the Number of particles in a Gas
Although the size can differ greatly between different gases
Avogadro's principle states that all gases that have the same number of particles will have the same volume. 1000 atoms of
Xenon will have the same volume as Helium. The molar volume for gases is the volume that 1 mole of gas will take up at 0
Celsius at 1.00 atm . Since all gases have the same volume at
STP (standard temperature and pressure) , this means that 1 mol of any gas will have a volume of 22.4L
.
** Conversion Factor:
1 mole = 22.4L at STP
STP = Standard temperature and pressure (temp = 0 o C, pressure = 1 atm)

Moles to Volume and Volume to Moles
Example1: What is the volume of a balloon that holds 1.78 moles of oxygen gas at STP?
Example 2: How many moles of helium at STP will fit into a
39.6 L container?

Volume to Particles and Particles to Volume
Example 1: How many particles are in 3.72 L of gas at STP?
Example 2: What volume is occupied by 3.24 x 10 24 molecules of H
2
O gas at STP?

Volume to Mass and Mass to Volume
Example 1: Determine the mass of 42.1L of NO
2(g)
@ STP.
Example 2: Determine the volume of the 1.00g of nitrogen gas at STP.

Comes from the Greek words stoicheion, meaning
element and metron, meaning measure.
In the real world, chemists perform reactions to make useful chemical compounds such as medicines, fibers, pigments, cosmetics and structural materials.
Because some reactants are expensive chemists don’t just mix huge quantities of chemicals together and hope for the best; rather they use stoichiometry to calculate the mass relationships between products and reactants.

Stoichiometry: The Study of relationships between the amounts of reactants used and products formed by a chemical reaction, based on the Law of Conservation of Mass.
mole ratio: The ratio of the product and reactant in a chemical reaction.
The numbers that fit into this ratio are pulled directly
out of the balanced equation for the reaction.

Mole ratios are the key to stoichiometric calculations.
They give us the ratios between the amounts of reactants and products in any given reaction.
We get mole ratios from the coefficients.
That’s why we need to start with a balanced
equation.

Chemical Equation:
2 Al(s) + 3Br
2
(l)  2AlBr
3
(s)
For every 2 moles of aluminum, 3 moles of bromine are used to produce the reaction.
** The Law of Conservation is important when dealing with stoichiometry. If the equation isn’t properly balanced then you will use the incorrect mole ratios in your calculations.

Example: Write all possible mole ratios
2 Al(s) + 3Br
2
(l)  2AlBr
3
(s)

What is a mole?
How big is a mole?
Who is Avogadro?
Molar/ Molecular Mass
Dimensional Analysis
- particles, volume, mass, moles
Law of Conservation of Mass
Steps to solve a stoichiometric equation. (Write a balanced chemical equation, convert to moles, use the mole ratio, and find what required.)

Make sure to BALANCE!
a) Al (s) + O
2 b) Fe (s) + H
2
(g)  Al
2
O
3
(s)
O (l)  Fe (s) + H
2 c) HgO (s)  Hg(l) + O
2
3
O
4
(g)
(g)

Moles of known x moles of unknown = moles of unknown moles of known

Example 1:
How many moles of H2 are we going to need to react with 12.0 moles of O2 to produce H2O2?
How much H2O2 will this produce?
Step 1: Write balanced equation
H
2
+ O
2
 H
2
O
2
Step 2: Write down what you are given and convert to moles.
Step 3: Use mole ratios to convert to desired chemical.

Example2:
How many moles of hydrogen are produced when 0.0400 mole of potassium is used?
2K(s) + 2H2O(l)  2KOH(aq) + H
2(g)

Particles  moles  Particles
**Always convert to moles first !
2K(s) + 2H2O(l)  2KOH(aq) + H
2(g)
How many atoms of H
2 are produced if you start with 3.02 x 10 22 atoms of H
2
O?

a) Determine the mass of sodium chloride produced when 1.25 grams of chlorine gas reacts with sodium.
2 Na (s) + Cl
2 (g)
 2NaCl (s)

b) The volume of chlorine needed in order to produce 26.0 L of NaCl.

c) Determine the volume of chlorine gas used when 1.25 grams of sodium chloride is produced.

2NaN
3
(s)  2Na(s) + 3N
2
(g) a) Determine all mole ratios.
b) Determine the mass of N
2
NaN is decomposed.
3 c) Determine the volume of N
2 atoms of NaN
3 are used. produced if 100.0 g of gas produced if 2.4 x10 d) How many moles of sodium are produced if 7.2 mol
23 of NaN
3 reacts?
e) What must you always convert to first?