1. U4 One Step Stoichiometry Problems
Chemistry Ms. Boon

2. Catalyst
Pick up the notes handout and answer the following question at the top of the page:
10 weeks have passed since the first day of school. How many days have passed? How do you know?
7 days = 1 week
10 weeks X
7 days
1 week =
70 days

3. Objective
I can perform one-step stoichiometry conversions using a worksheet, notes, and a puzzle.
I can show my work and use units in all my calculations.

4. Mini Review: What is the mole?
The mole is a number we use to make counting atoms, ions, and molecules much easier. The mole allows scientists to count by weighing.
Think, Pair, Share: What is counting by weighing? Imagine you work at a candy store and a customer asks for 500 jelly beans. There is a long line and you do not want to count 500 beans. But you have a scale. What can you do?
Answer: Find the weight of one bean. Then multiply by Finally, measure this mass of beans and it should be 500 beans.

5. Mini Review: What is the mole?
1 mole = 6.02 x 1023 particles. This does not change.
The number of particles in 1 mole is called Avogadro’s number
It does not matter what you are counting. 1 mole of something contains 6.02 x 10^23 particles of that thing.

6. THE MOLE -- Why? Why is the mole useful to us as chemists??
Make a dot on your paper with your pencil.
Guess how many atoms of Carbon graphite are in that dot.
25 million atoms in that tiny dot!

7. Mini Review: What is the mole?
Molar mass and molecular weight are the mass in grams of one mole of an element or compound.
Different elements and compounds have different molar masses or molecular weights.
Example 1: What is the molar mass of aluminum? Hint: The molar mass is the same as the atomic mass, just add “g” for grams.
Example 2: What is the molecular weight of baking soda? Hint: First find the mass of each element, then multiply by subscripts, then add up the answers.
Emphasize the units – g/mol grams per mole -- this means grams in one mole
Answer g/mol
Answer NaHCO3 = 84 g/mol

8. Mini Review: What is the mole?
Example 2: What is the molecular weight of baking soda? Hint: First find the mass of each element, then multiply by subscripts, then add up the answers.
Answer NaHCO3 = 84 g/mol
16 g
x 3
48 g
23 g
x 1
1 g
x 1
12 g
x 1 + +
= 84 g/mol +
5 minute - Quick Practice: Choose at least 2 molar mass/molecular weight problems from your worksheet.

9. Stoichiometry Conversions Part 1: Grams to Moles and Moles to Grams.
Calculating the molar mass or molecular weight of a chemical reveals the mass of one mole of that chemical. What if we are given more than one mole of a substance? Or some random amount in grams? Use the molar mass or molecular weight as a conversion factor to move between moles and grams.
Ex 1: Moles to Grams. How many moles is 24 g of carbon?
Ex 2: Grams to Moles. How many grams is 10 moles of Gold?
Given: 24 g
Unknown: # moles
Conversion: 1 mol/12 g
Set up: 24 g x 1 mol =
12 g
Answer: 2 mol
Given: 10 mol
Unknown: # g
Conversion: 197g/1 mol
Set up: 10 mol x 197 g =
1 mol
Answer: 1970 g
Emphasize the set up of the problem. You have to set up the given first. Then multiply my the molar mass conversion factor. The conversion factor is multiplied so that the given units cancel out.
5 minute - Quick Practice: Choose at least 2 gram to mole or mole to gram problems from your worksheet.

10. Stoichiometry Conversions Part 2: Particles to Moles and Moles to Particles.
Avogadro’s number allows us to determine the number of atoms, molecules, or ions (generally particles) in a given sample. Use 1 mole = 6.02 x as a conversion factor to move between moles and particles.
Ex 1: Particles to Moles. How many moles is 1.20 x 1024 atoms of carbon?
Given: 1.20 x 1024 atoms
Unknown: # moles
Conversion: 1 mol/6.02 x 1023 atoms
Set up: 1.20 x 1024 atoms x 1 mol =
6.02 x 1023 atoms
Answer: 2 mol
Emphasize the set up of the problem. You have to set up the given first. Then multiply by the avogadro’s number conversion factor. The conversion factor is multiplied so that the given units cancel out.

11. Stoichiometry Conversions Part 2: Particles to Moles and Moles to Particles.
Avogadro’s number allows us to determine the number of atoms, molecules, or ions (generally particles) in a given sample. Use 1 mole = 6.02 x as a conversion factor to move between moles and particles.
Ex 2: Moles to Particles. How many atoms is 10 moles of Gold?
Given: 10 mol
Unknown: # atoms
Conversion: 6.02 x 1023 /1 mol
Set up: 10 mol x 6.02 x 1023 atoms=
1 mol
Answer: 6.02 x 1024 atoms
Emphasize the set up of the problem. You have to set up the given first. Then multiply my the molar mass conversion factor. The conversion factor is multiplied so that the given units cancel out.
5 minute - Quick Practice: Choose at least 2 particle conversion problems from your worksheet.

12. Extra Special Bonus: Video Review – Super Hero Science
How does the law of conservation of mass limit the size of a super hero?
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13. More Practice See textbook p. 224-233
Try the sample problems on p. 228 and 229