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StoichiometryStoichiometry

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

1. Review the conversion of particles or grams to moles

2. Determine mole ratios from a balanced chemical equation

3. Determine the amount of product produced when given the amount of reactants

Review the Molar Mass of Review the Molar Mass of CompoundsCompounds

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 Cl 110.98 g/mol CaCl2

17Cl

35.45

20

Ca  40.08

PracticePractice

Calculate the Molar Mass of calcium phosphate◦Formula = ◦Masses elements:

◦Molar Mass =310.18 g

Ca3(PO4)2

CalculationsCalculations

molar mass Avogadro’s

number Grams MolesMoles

Particles

Everything must go through Moles!!!Everything must go through Moles!!!

FlowchartFlowchartAtoms or Molecules

Moles

Mass (grams)

Divide by 6.02 X 1023

Multiply by 6.02 X 1023 Multiply by

atomic/molar mass from periodic tableDivide by

atomic/molar mass from periodic table

Cookies and Chemistry…Huh!?!?Cookies and Chemistry…Huh!?!?

Just like chocolate chip Just like chocolate chip cookies have recipes, cookies have recipes, chemists have recipes as wellchemists have recipes as well

Instead of calling them Instead of calling them recipes, we call them recipes, we call them reaction/equationsreaction/equations

Furthermore, instead of using Furthermore, instead of using cups and teaspoons, we use cups and teaspoons, we use molesmoles

Lastly, instead of eggs, Lastly, instead of eggs, butter, sugar, etc. we use butter, sugar, etc. we use chemical compounds as chemical compounds as ingredientsingredients

Chocolate Chip Cookies!!Chocolate Chip Cookies!!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 chipsMakes 3 dozenHow 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 1½ cups white sugar?

Mole RatiosMole Ratios

These mole ratios can be used to calculate the moles of one chemical from the given amount of a different chemical

Are obtained by comparing the coefficients in a balanced chemical equation.

Chemistry Recipes – Page 11Chemistry Recipes – Page 11

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!

_Cl2 + _Ag _AgCl

If there are 5 moles of Ag, how many moles of Cl2?

Practice – Page 11Practice – Page 11

__Fe(OH)3 __Fe2O3 + __H2O

If 6 moles react:a)How many moles of iron (III) oxide?

b)How many moles of water?

Practice – Page 12Practice – Page 12

_SiO2 + _HF _SiF4 + _H2O

Mole ratios?

a)25 moles of SiO2 converts to how many moles of SiF4?

““Mole Relationships” LabMole Relationships” LabLead (II) nitrate and sodium

iodide ????

Which test tube will produce the max amount?Test #1

Test #2

Test #3

Test #4

Test #5

1.5:4.5

2:4 3:3 4:2 4.5:1.5

Mass-Mass ConversionsMass-Mass Conversions

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.

Mass-Mass Conversion – Page 17Mass-Mass Conversion – Page 17

__Fe + __S8 __FeS

How many grams of iron are required to make 86.7g of FeS.

How many moles of sulfur are needed?

Practice Mass-Mole-Mass – Page 17 Practice Mass-Mole-Mass – Page 17 #2#2

_CS2 + _Cl2 _CCl4 + _S2Cl2

If 17.6g of carbon disulfide react with an excess of chlorine, how many grams of disulfur dichloride will result?

Practice Mass-Mole-Mass – Page 17 Practice Mass-Mole-Mass – Page 17 #3#3

_P4 + _O2 _P4O10

How many grams of phosphorous will react with 25g of oxygen?

Stoichiometry : Mole Ratios to Stoichiometry : Mole Ratios to Determining Grams of ProductDetermining Grams of ProductLet’s see if you can:Let’s see if you can:

1. Review the conversion of particles or grams to moles

2. Determine mole ratios from a balanced chemical equation

3. Determine the amount of product produced when given the amount of reactants

Mass-Mole-Molecules: Determine Mass-Mole-Molecules: Determine the number of molecules in 73 g of the number of molecules in 73 g of waterwater

73 g H2O

# H2O molecules =

x 1 mol H2O

18.02 g H2O

= 2.4 x 1024 molecules H2O

x 6.02x1023 molecules

1 mol H2O

Try this one:Try this one:

Calculate the mass in grams of iodine required to react completely with 0.50 moles of aluminum.

Al + I2 AlI32 Al + 3 I2 2 AlI3

= 190 g I2

0.50 mol Al x 3 mol I2 2 mol Al

x 253.80 g I2

1 mol I2

Try this one:Try this one:

Calculate the mass in grams of iodine required to react completely with 0.50 g of aluminum.

Al + I2 AlI32 Al + 3 I2 2 AlI3

= 7.1 g I2

x 3 mol I2 2 mol Al

x 253.80 g I2

1 mol I2

0.50 g Al x 1 mol Al

26.98 g Al