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the Mole !

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Itâ€™s time to learn about . . .

the Mole !

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Stoichiometry : Mole Ratios to Determining Grams of ProductAt the conclusion of our time together, you should be able to:

- Review the conversion of particles or grams to moles
- Determine mole ratios from a balanced chemical equation
- Determine the amount of product produced when given the amount of reactants

- The molar mass (MM) of a compound is determined by adding up all the atomic masses for the molecule (or compound)
- Ex. Molar mass of CaCl2
- Avg. Atomic mass of Calcium = 40.08g
- Avg. Atomic mass of Chlorine = 35.45g
- Molar Mass of calcium chloride = 40.08 g/mol Ca + (2 X 35.45) g/mol Clïƒ 110.98 g/mol CaCl2

20

Ca40.08

17Cl 35.45

- Calculate the Molar Mass of calcium phosphate
- Formula =
- Masses elements:
- Molar Mass =
310.18 g

Ca3(PO4)2

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molar mass Avogadroâ€™s number Grams Moles Particles

Everything must go through Moles!!!

Atoms or Molecules

Divide by 6.02 X 1023

Multiply by

6.02 X 1023

Multiply by atomic/molar mass from periodic table

Moles

Divide by atomic/molar mass from periodic table

Mass (grams)

1 cup butter 2 eggs

1/2 cup white sugar 1 teaspoon salt

1 cup packed brown sugar

1 teaspoon vanilla extract

2 1/2 cups all-purpose flour

1 teaspoon baking soda

2 cups semisweet chocolate chips

Makes 3 dozen

How many eggs are needed to make 3 dozen cookies?

How much butter is needed for the amount of chocolate chips used?

How much brown sugar would I need if I had 1Â½ cups white sugar?

- Just like chocolate chip cookies have recipes, chemists have recipes as well
- Instead of calling them recipes, we call them chemical equations
- Furthermore, instead of using cups and teaspoons, we use moles
- Lastly, instead of eggs, butter, sugar, etc. we use chemical compounds as ingredients

- Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe)
- Be sure you have a balanced reaction before you start! Balance #1 on your worksheet!!
- Example: 2 Ag+ Cl2 ïƒ 2 AgCl
- This reaction tells us that by mixing 2 moles of silver with 1 mole of chlorine we will get 2 moles of silver chloride
- What if we wanted 4 moles of AgCl?
- 10 moles?
- 50 moles?

Letâ€™s sit down and figure this out!!

- Write the balanced reaction for hydrogen gas reacting with oxygen gas.
2 H2 + O2ïƒ 2 H2O

- How many moles of reactants are needed?
- What if we wanted 4 moles of water?
- What if we had 3 moles of oxygen, how much hydrogen would we need to react, and how much water would we get?
- What if we had 50 moles of hydrogen, how much oxygen would we need, and how much water would be produced?

- These mole ratios can be used to calculate the moles of one chemical from the given amount of a different chemical
- Example: How many moles of chlorine are needed to react with 5 moles of silver (without any silver left over)?
2 Ag + Cl2ïƒ 2 AgCl

5 Ag + 2.5 Cl2ïƒ 5 AgCl

x 1 mol Cl2

2 mol Ag

2 Ag+ Cl2ïƒ 2 AgCl

# moles of Cl2 =

5 mol Ag

= 2.5 mol Cl2

2 mol AgCl

1 mol Cl2

- How many moles of silver chloride will be produced if you react 2.6 moles of chlorine gas with an excess (more than you need) of silver metal?
2 Ag + Cl2ïƒ 2 AgCl

# moles of AgCl =

2.6 mol Cl2 x

= 5.2 mol AgCl

- We can also start with mass and convert to moles of product or another reactant
- We use molar mass and the mole ratio to get to moles of the compound of interest
- Calculate the number of moles of the combustion of ethane (C2H6) needed to produce 10.0 g of water
- 2 C2H6 + 7 O2ïƒ 4 CO2 + 6 H20

x 2 mol C2H6

6 mol H2O

x 1 mol H2O

18.02 g H2O

- 2 C2H6 + 7 O2ïƒ 4 CO2 + 6 H20

10.0 g H2O

= 0.185 mol C2H6

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Stoichiometry : Mole Ratios to Determining Grams of ProductAt the conclusion of our time together, you should be able to:

- Review the conversion of particles or grams to moles
- Determine mole ratios from a balanced chemical equation
- Determine the amount of product produced when given the amount of reactants

- Most often we are given a starting mass and want to find out the mass of a product we will get (called theoretical yield) or how much of another reactant we need to completely react with it (no leftover ingredients!)
- Now we must go from grams to moles, to mole ratios, and back to grams of the compound we are interested in.

- Ex. Calculate how many grams of ammonia are produced when you react 2.00 g of nitrogen with excess hydrogen.
- N2 + 3 H2 ïƒ 2 NH3

2.00 g N2 1 mol N2 2 mol NH3 17.04 g NH3

28.02 g N2 1 mol N2 1 mol NH3

= 2.43 g NH3

- How many grams of calcium nitride are produced when 2.00 g of calcium reacts with an excess of nitrogen?
- Ca + N2ïƒ Ca3N2
- 3 Ca + N2ïƒ Ca3N2

x 1 mol Ca3N2

x 148.26 g Ca3N2

3 mol Ca

1 mol Ca3N2

x 1 mol Ca

40.08 g Ca

- 3 Ca + N2ïƒ Ca3N2

2.00 g Ca

= 2.47 g Ca3N2

Some Things Just Take a Lot of Work!!!

Stoichiometry : Mole Ratios to Determining Grams of ProductLetâ€™s see if you can:

- Review the conversion of particles or grams to moles
- Determine mole ratios from a balanced chemical equation
- Determine the amount of product produced when given the amount of reactants

x 3 mol N2

x 28.02 g N2

2 mol NaN3

1 mol N2

x 1 mol NaN3

65.02 g NaN3

- NaN3ïƒ Na + N2
- Decomposition
- 2 NaN3ïƒ 2 Na + 3 N2
- 65.02 g 22.99 g28.02 g

94.5 g NaN3

= 61.1 g N2

Donâ€™t you just love these types of problems???