StoichiometryStoichiometry

The MoleThe Mole

A counting unitA counting unit Similar to a dozen, except instead Similar to a dozen, except instead

of 12, it’s of 12, it’s 602,000,000,000,000,000,000,000602,000,000,000,000,000,000,000

6.02 X 106.02 X 1023 23 (in scientific notation)(in scientific notation) This number is named in honor of This number is named in honor of

Amedeo Avogadro (1776 – 1856)Amedeo Avogadro (1776 – 1856)

The Mass of 1 mole (in grams)The Mass of 1 mole (in grams)

Equal to the numerical value of the average Equal to the numerical value of the average

atomic mass (get from periodic table), or add atomic mass (get from periodic table), or add

the atoms together for a moleculethe atoms together for a molecule

1 mole1 mole of C atoms of C atoms = = 12.0 g12.0 g

1 mole1 mole of Mg atoms of Mg atoms == 24.3 g24.3 g

11 mole mole of O of O22 molecules molecules == 32.0 g32.0 g

Molar MassMolar Mass

Molar Mass of CompoundsMolar Mass of Compounds

The molar mass (MM) of a compound is The molar mass (MM) of a compound is determined the same way, except now you add determined the same way, except now you add up all the atomic masses for the molecule (or up all the atomic masses for the molecule (or compound)compound)Ex. Molar mass of CaClEx. Molar mass of CaCl22Avg. Atomic mass of Calcium = 40.08gAvg. Atomic mass of Calcium = 40.08gAvg. Atomic mass of Chlorine = 35.45gAvg. Atomic mass of Chlorine = 35.45gMolar Mass of calcium chloride = Molar Mass of calcium chloride =

40.08 g/mol Ca + (2 X 35.45) g/mol Cl40.08 g/mol Ca + (2 X 35.45) g/mol Cl 110.98 g/mol CaCl 110.98 g/mol CaCl22

20

Ca  40.08 17

Cl 35.45

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

PracticePractice

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

Ca: 3 Ca’s X 40.1 = Ca: 3 Ca’s X 40.1 = P: 2 P’s X 31.0 = P: 2 P’s X 31.0 = O: 8 O’s X 16.0 = O: 8 O’s X 16.0 =

Molar Mass = Molar Mass =

Ca3(PO4)2

120.3 g

62.0 g

128.0 g

120.3g + 62.0g +128.0g310.3 g/mol

molar mass Avogadro’s numbermolar mass Avogadro’s number Grams Grams MolesMoles particles particles

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

CalculationsCalculations

Atoms/Molecules and GramsAtoms/Molecules and Grams

How many moles of Cu are How many moles of Cu are present in 35.4 g of Cu?present in 35.4 g of Cu?

How many atoms?How many atoms?

Learning Check!Learning Check!

What is the mass (in grams) of What is the mass (in grams) of 1.20 X 101.20 X 102424 molecules of molecules of glucose (Cglucose (C66HH1212OO66)?)?

Chocolate Chip Cookies!!Chocolate Chip Cookies!!1 cup butter

1/2 cup white sugar

1 cup packed brown sugar

1 teaspoon vanilla extract

2 eggs

2 1/2 cups all-purpose flour

1 teaspoon baking soda

1 teaspoon salt

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 many eggs would we need to make 9 dozen cookies?

How much brown sugar would I need if I had 1 ½ cups white sugar?

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 reaction recipes, we call them reaction equationsequations

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

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

Chemistry RecipesChemistry Recipes

Looking at a reaction tells us how much of Looking at a reaction tells us how much of something you need to react with something you need to react with something else to get a product (like the something else to get a product (like the cookie recipe)cookie recipe)

Be sure you have a balanced reaction Be sure you have a balanced reaction before you start!before you start!

Example: 2 Na + ClExample: 2 Na + Cl2 2 2 NaCl 2 NaClThis reaction tells us that by mixing 2 moles of This reaction tells us that by mixing 2 moles of

sodium with 1 mole of chlorine we will get 2 moles sodium with 1 mole of chlorine we will get 2 moles of sodium chlorideof sodium chloride

What if we wanted 4 moles of NaCl? 10 moles? What if we wanted 4 moles of NaCl? 10 moles? 50 moles?50 moles?

PracticePractice

Write the balanced reaction for hydrogen gas Write the balanced reaction for hydrogen gas reacting with oxygen gas.reacting with oxygen gas.

2 H2 H22 + O + O22 2 H 2 H22OO How many moles of reactants are needed?How many moles of reactants are needed? What if we wanted 4 moles of water?What if we wanted 4 moles of water? What if we had 3 moles of oxygen, how much hydrogen What if we had 3 moles of oxygen, how much hydrogen

would we need to react and how much water would we would we need to react and how much water would we get?get?

What if we had 50 moles of hydrogen, how much oxygen What if we had 50 moles of hydrogen, how much oxygen would we need and how much water produced? would we need and how much water produced?

2 mol H2 1 mol O2

4 mol H2

2 mol O2

6 mol H2, 6 mol H2O

25 mol O2, 50 mol H2O

Mole RatiosMole Ratios

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

Example: How many moles of chlorine is Example: How many moles of chlorine is needed to react with 5 moles of sodium (without needed to react with 5 moles of sodium (without any sodium left over)?any sodium left over)?

2 Na + Cl2 Na + Cl22 2 NaCl 2 NaCl

5 moles Na 1 mol Cl2

2 mol Na= 2.5 moles Cl2

Mole-Mole ConversionsMole-Mole ConversionsHow many moles of sodium chloride will How many moles of sodium chloride will

be produced if you react 2.6 moles of be produced if you react 2.6 moles of chlorine gas with an excess (more than chlorine gas with an excess (more than you need) of sodium metal?you need) of sodium metal?

2 Na + Cl2 Na + Cl22 2 NaCl 2 NaCl

2.6 moles Cl2 2 mol NaCl

1 mol Cl2= 5.2 moles NaCl

Mole-Mass ConversionsMole-Mass Conversions

Most of the time in chemistry, the amounts are Most of the time in chemistry, the amounts are given in grams instead of molesgiven in grams instead of moles

We still go through moles and use the mole ratio, We still go through moles and use the mole ratio, but now we also use molar mass to get to gramsbut now we also use molar mass to get to grams

Example: How many grams of chlorine are required Example: How many grams of chlorine are required to react completely with 5.00 moles of sodium to to react completely with 5.00 moles of sodium to produce sodium chloride?produce sodium chloride?

2 Na + Cl2 Na + Cl22 2 NaCl 2 NaCl

5.00 moles Na 1 mol Cl2 70.90g Cl2

2 mol Na 1 mol Cl2

= 177g Cl2

You PracticeYou Practice

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

2 Al + 3 I2 Al + 3 I2 2 2 AlI 2 AlI3 3

Mass-MoleMass-MoleWe can also start with mass and convert to We can also start with mass and convert to

moles of product or another reactantmoles of product or another reactantWe use molar mass and the mole ratio to get We use molar mass and the mole ratio to get

to moles of the compound of interestto moles of the compound of interestCalculate the number of moles of ethane (CCalculate the number of moles of ethane (C22HH66) )

needed to produce 10.0 g of waterneeded to produce 10.0 g of water 2 C2 C22HH66 + 7 O + 7 O22 4 CO 4 CO22 + 6 H + 6 H220 0

10.0 g H2O 1 mol H2O 2 mol C2H6

18.0 g H2O 6 mol H20

= 0.185 mol C2H6

Mass-Mass ConversionsMass-Mass Conversions

Most often we are given a starting mass Most often we are given a starting mass and want to find out the mass of a product and want to find out the mass of a product we will get (called theoretical yield) or how we will get (called theoretical yield) or how much of another reactant we need to much of another reactant we need to completely react with it (no leftover completely react with it (no leftover ingredients!)ingredients!)

Now we must go from grams to moles, Now we must go from grams to moles, mole ratio, and back to grams of mole ratio, and back to grams of compound we are interested incompound we are interested in

Mass-Mass ConversionMass-Mass Conversion

Ex. Calculate how many grams of Ex. Calculate how many grams of ammonia are produced when you react ammonia are produced when you react 2.00g of nitrogen with excess hydrogen.2.00g of nitrogen with excess hydrogen.

NN2 2 + 3 H+ 3 H2 2 2 NH 2 NH33

2.00g N2 1 mol N2 2 mol NH3 17.06g NH3

28.02g N2 1 mol N2 1 mol NH3

= 2.4 g NH3

PracticePractice

How many grams of calcium nitride are How many grams of calcium nitride are produced when 2.00 g of calcium reacts produced when 2.00 g of calcium reacts with an excess of nitrogen?with an excess of nitrogen?