StoichiometryStoichiometry

Chapter 12 NotesChapter 12 Notes

Review - The MoleReview - The 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 of substance (in grams)

Equal to the numerical value of the average

atomic mass (get from periodic table), or add

the atoms together for a molecule

1 mole of C atoms = 12.01 g

1 mole of Mg atoms = 24.31 g

1 mole of O2 molecules = 32.00 g

1 mole of BCl3 molecules = 117.17 g

Review - Molar MassReview - Molar Mass

Molar Mass of CompoundsMolar Mass of Compounds

The molar mass The molar mass (MM) (MM) of a compound is 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 compoundup all the atomic masses for the compoundEx. Molar mass of Ex. Molar mass of CaClCaCl22Avg. 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 Cl 40.08 g/mol Ca + (2 x 35.45) g/mol Cl

110.98 g/mol CaCl110.98 g/mol CaCl22

20

Ca  40.08

17Cl

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 40.08 = Ca: 3 Ca’s X 40.08 = P: 2 P’s X 30.97 = P: 2 P’s X 30.97 = O: 8 O’s X 16.00 = O: 8 O’s X 16.00 =

Molar Mass = Molar Mass =

Ca3(PO4)2

120.24 g

61.94 g

128.00 g

120.24g + 61.94g +127.00g310.18 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 Grams

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

35.4 g Cu 1 mol Cu 6.02 X 1023 atoms Cu 63.5 g Cu 1 mol Cu

= 3.36 X 1023 atoms Cu

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!!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 chipsMakes 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!?!? Just like chocolate chip cookies Just like chocolate chip cookies

have recipes, chemists have have recipes, chemists have recipes as wellrecipes as well

Instead of calling them recipes, Instead of calling them recipes, we call them we call them reaction 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 sugar, etc. we use chemical chemical compoundscompounds as ingredients as ingredients

Chemistry RecipesLooking 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)

The study of the quantative relationships The study of the quantative relationships among the among the amountsamounts of reactants used and of reactants used and the amounts of the amounts of productsproducts formed by a formed by a chemical reaction is called chemical reaction is called

STOICHIOMETRYSTOICHIOMETRY

Chemistry Recipes

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

Example: Example: 2 Na2 Na + + ClCl22 2 NaCl2 NaClThis reaction tells us that by mixing This reaction tells us that by mixing 2 moles of 2 moles of

sodiumsodium with with 1 mole of chlorine 1 mole of chlorine we will get we will get 2 moles 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 Ratios

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

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

Mole-Mass Conversions

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

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

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

2 Na + Cl2 2 NaCl

5.00 moles Na 1 mol Cl2 70.90g Cl2

2 mol Na 1 mol Cl2

= 177g Cl2

PracticePractice

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-MoleWe can also start with mass and convert to

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

to moles of the compound of interestCalculate the number of moles of ethane (C2H6)

needed to produce 10.0 g of water 2 C2H6 + 7 O2 4 CO2 + 6 H20

10.0 g H2O 1 mol H2O 2 mol C2H6

18.0 g H2O 6 mol H20

= 0.185 mol C2H6

PracticePracticeCalculate how many moles of oxygen are Calculate how many moles of oxygen are

required to make 10.0 g of aluminum oxiderequired to make 10.0 g of aluminum oxide4 Al + 3 O4 Al + 3 O2 2 2 Al 2 Al22OO3 3

Mass-Mass Conversions

Most often we are given a Most often we are given a starting mass starting mass and want to find out the mass of a and want to find out the mass of a productproductThis is called the This is called the theoretical yieldtheoretical yield… or how … or how

much of another reactant we need to much of another reactant we need to completely react (completely react (with no leftover ingredients!)with no leftover ingredients!)

Now we must go from grams to moles, to Now we must go from grams to moles, to the mole ratio, and back to grams of the the mole ratio, and back to grams of the 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

Practice

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

3 Ca + N2 Ca3N2