1. STOICHIOMETRY
the study of the quantitative aspects of chemical reactions
(the mathematics of chemical reactions)

2. Why Is It Important?
It allows us to predict how much of a reactant is consumed or product made in a chemical reaction
It allows us to determine how much reactant will be needed to generate a specified amount of product
Very important if a reactant is expensive; using too much wastes money
It allows us to determine how much of an unwanted product is generated
Very important to minimize this when we’re dealing with medicines
Also important if getting rid of the unwanted product is expensive

3. Essential Questions What is a mole?
How do we calculate # of moles from # of atoms and vice versa?
Why do we need moles?
What is molar mass?
How do we calculate the molar mass of an element or a compound?

4. Let’s relate to something we know
What is the relationship between the following words:
1 dozen
1 century
1 decade
What do you need to figure out the mass of a dozen eggs if each egg is 10 grams?

5. Suppose… we invented a new collection unit called a rapp.
One rapp contains 8 objects.
1. How many paper clips in 1 rapp?
8 paper clips
2. How many oranges in 2.0 rapp?
16 oranges
3. How many rapps contain 40 gummy bears?
5 rapps

6. What is a Mole? A) A blind furry animal A brown mark on your body
C) A double agent
D) An important chemistry concept
E) All of the above

7. Sorry … we are only going to focus on the chemistry concept …
The correct answer is E!
Sorry … we are only going to focus on the chemistry concept …

8. A Mole Is Just a Number (a way to count units of something)
Just like …
A pair = 2
A dozen = 12
A baker’s dozen = 13
A gross = 144
A ream = 500
… a mole = 602,000,000,000,000,000,000,000

9. Not Just Any Number …
6.02x1023
Avogadro’s Number

10. Why Avogadro?
Named after Amedeo Avogadro who studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present at similar conditions
This is oversimplified
We will revisit it when we study gases

11. Definition of Avogadro’s Number
The number of atoms in exactly grams of the carbon-12 isotope.
(nice to know, but not need to know)

12. Just How Big a Number is a Mole?
A mole of M&M’s would cover the continental United States to a depth of 125 km (~77 miles).
If the 7 billion people on Earth were to do nothing but count the gumballs in one mole at the rate of one gumball per second, it would take over 2.7 million years to count all the gumballs.

13. The Most Important Thing to Remember
A MOLE IS A NUMBER!

14. The Mole (mol) is an SI Unit
It is the SI unit for the amount of a substance
One mole = 6.02 x 1023 particles
One mole of eggs = 6.02 x 1023 eggs
One mole of cookies = 6.02 X 1023 cookies
One mole of cars = 6.02 X 1023 cars
One mole of Al atoms = 6.02 X 1023 atoms
Notice that the NUMBER is always the same, but the MASS can be very different!

15. Check for understanding
Number of atoms in mole of Al
a) 500 Al atoms
b) x 1023 Al atoms
c) x 1023 Al atoms
Number of moles of S in 1.8 x 1024 S atoms
a) 1.0 mole S atoms
b) 3.0 mole S atoms
c) 1.1 x 1048 mole S atoms

16. Check for Understanding
How many atoms are present in 3.7 mol of sodium?
2.2 x 1024 Na atoms
How many atoms are present in 155 mol of arsenic?
9.33 x 1025 As atoms
How many moles of xenon in 5.66 x 1026 atoms?
940. mol Xe

17. A Mole of Particles Contains 6.02 x 1023 Particles
Regardless of what particles they are
1 mol C = 6.02 x 1023 C atoms
1 mol H2O = 6.02 x 1023 H2O molecules
1 mol NaCl = 6.02 x 1023 NaCl compounds*
*technically, ionics are compounds but not molecules, so they are called formula units)
*6.02 x 1023 Na+ ions & 6.02 x 1023 Cl– ions

18. Why are Moles Important?
In chemistry, we don’t work with individual atoms or molecules or ions because they are TOO SMALL to be weighed or measured
To measure these atoms or molecules or ions, we have to work with LOTS of them
That’s where the MOLE comes in 6.02X1023 (a mole) is a practical # of particles to use because this quantity can be weighed more conveniently

19. Then and Now … THEN
When we talked about atoms – we used the atomic mass unit to measure the mass of an atom
It is based on the mass of a carbon-12 atom
We used the atomic mass from the periodic table as the weight of an atom of an element (in amu)

20. Then and Now … NOW
Recall that the # of atoms in a mole is also based on a carbon-12 atom
So, it is reasonable to extrapolate the mass of one atom (in amu) to the mass of one mole of atoms (in grams)

21. Molar Mass of an Element
the mass of 1 mole of an element
units = grams/mole
numerically equal to the atomic mass (taken from the periodic table)
So…the atomic mass from the periodic table can also be used as the mass of one mole!

22. Molar Mass Example: Elements
1 mole of C atoms = 12.0 g
1 mole of Mg atoms = 24.3 g
1 mole of Cu atoms = 63.5 g
(Note: these values are taken directly from the periodic table)

23. Practice Find the molar mass of the following:
2 moles of Na atoms = g
3 mole of Sn atoms = g
4 moles of He atoms = 16.0 g

24. Molar Mass of a Compound (Ionic or Covalent)
the mass of 1 mole of a compound
units = grams/mole
numerically equal to the sum of the atomic masses (taken from the periodic table)

25. Molar Mass Example: Compounds
1 mole of CaCl2 compound:
1 mole of Ca2+ ions = 40.1 g
2 moles of Cl- ions = 2*35.5 g
TOTAL = = g
(Note: these values are taken directly from the periodic table)

26. Check for Understanding
What is the molar mass of N2O4?
What is the molar mass of K2O?
What is the molar mass of Al(OH)3?
What is the molar mass of (NH4)2SO4?

27. Answers N2O4 = 92.0 grams/mole K2O = 94.2 grams/mole
1 mole of N2O4 = 92g = 6.02x1023 particles
K2O = 94.2 grams/mole
1 mole of K2O = 94.2g = 6.02x1023 particles
Al(OH)3 = 78.0 grams/mole
1 mole of Al(OH)3 = 78.0g = 6.02x1023 particles

28. Mole Jokes! Who is Avogadro’s favorite actor?
Mol Gibson…. Get it? Ha!Ha!
Where did Avogadro go on Saturday?
The shopping mole… Wacka!Wacka!
What did Avogadro have on his pancakes?
Molasses …
Why did Avogadro look forward to the year 2000?
It was the start of the new molennium …

30. Stop
Work with a partner and practice calculating moles and molar mass on:
Try these problems
Worksheet: The Mole and Avogadro's number
Worksheet 11-2

31. Why do we use moles?
We know that lab balances don’t directly weigh moles
Balances weigh in grams
We also know that lab balances can’t weigh individual atoms/molecules/ions – or even hundreds or thousands of them
These particles are too small to be weighed on balances 31

32. Why do we use moles?
The mole is a link between the microscopic (atoms and molecules) and the macroscopic (grams).
We will use the concept of the mole to be able to move between grams and number of atoms or molecules!

33. Everything must go through Moles!!!
Conversions!
Everything must go through Moles!!!
molar mass Avogadro’s number Grams Moles particles 33

34. Use molar mass to convert moles to grams
Example
moles → grams
Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?
Use molar mass to convert moles to grams 34

35. Use molar mass to convert grams to moles
Example
grams → moles
The artificial sweetener aspartame (Nutra-Sweet) formula C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame?
Use molar mass to convert grams to moles 35

36. Example How many atoms of K are present in 78.4 g of K? grams → atoms
Convert grams to moles
Then convert moles to atoms 36

37. Convert molecules to moles Then convert moles to grams
Example
molecules → grams
What is the mass (in grams) of 1.20 X 1024 molecules of glucose (C6H12O6)?
Convert molecules to moles
Then convert moles to grams 37

38. Stop Work with a partner to complete: Try these on your own
Moles and Mass
Mixed Mole Problems
HW: ChemQuest 30