Start Up

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Start Up

• What does a dozen mean?
• How many eggs are 3 dozen?
• How many eggs are in 9.4 dozen?

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Chapter 11 12

• Moles and Stoichiometry

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BookworkDue 4/30/09 Test 4/30/09

• THE MOLE (Chapter 11)
• Read pg 309-337
• Problems 6, 8, 14-16, 20, 23, 36, 47, 52, 59,
  91, 99, 101d, 103b, 121
• STOICHIOMETRY (Chapter 12)
• Read pg 353-373
• Problems 45-58, 63, 77, 78, 81, 82, 84, 85, 86

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Chapter 11 Core Content Terms

• Mole
• Avogadros Number
• Molar Mass
• STP (Standard Temperature and Pressure)
• Molar volume
• Percent composition

• Empirical formula
• Limiting reactant
• Excess reactant (opposite of limiting)
• Theoretical Yield
• Actual Yield
• Percent yield

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What is the Mole?

• A counting number (like a dozen)
• Avogadros number (NA)
• 1 mol 6.02 ? 1023 items

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HOW LARGE IS IT???

• 1 mole of hockey pucks would equal the mass of
  the moon!

• 1 mole of basketballs would fill a bag the size
  of the earth!

• 1 mole of pennies would cover the Earth 1/4 mile
  deep!

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What do we do with it?

• Eventually, will use to find the number of atoms,
  molecules, or things in a mass.
• Example How many molecules are in 10 grams of a
  metal?
• Need to learn a few things 1st

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Molar Mass

• Mass of 1 mole of an element or compound.
• Atomic mass tells the...
• atomic mass units per atom (amu)
• grams per mole (g/mol)
• Round to 2 decimal places

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Calculating Formula Mass (Molar Mass)
Calculate the formula mass of magnesium
carbonate, MgCO3. (Use periodic table masses)
24.31 g 12.01 g 3(16.00 g)
84.32 g
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Molar Mass Examples

• carbon
• aluminum
• zinc

12.01 g/mol 26.98 g/mol 65.39 g/mol
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Molar Mass Examples

• water
• sodium chloride

• H2O
• 2(1.01) 16.00 18.02 g/mol
• NaCl
• 22.99 35.45 58.44 g/mol

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More Molar Mass Examples

• sodium bicarbonate
• sucrose

• NaHCO3
• 22.99 1.01 12.01 3(16.00) 84.01
  g/mol
• C12H22O11
• 12(12.01) 22(1.01) 11(16.00) 342.34
  g/mol

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Start Up

• What is the molar mass of Cu(OH)2.
• How many grams are in 23.6 moles of
• copper (II) hydroxide?

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Calculations with Molar Mass

• molar mass
• Grams Moles

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Converting Moles and Grams

• Aluminum is often used for the structure of
  light-weight bicycle frames. How many grams of
  Al are in 3.00 moles of Al?
• 3.00 moles Al ? g Al

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• 1. Molar mass of Al 1 mole Al 27.0 g Al
• 2. Conversion factors for Al
• 27.0g Al or 1 mol Al
• 1 mol Al 27.0 g Al
• 3. Setup 3.00 moles Al x 27.0 g Al
• 1 mole Al
• Answer 81.0 g Al

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Practice!
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Make a Mole!
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More Conversions!

• We are ready to go from g to molecules!

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Start Up

• How many grams are in 23.6 moles of
• copper (II) hydroxide?

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Atoms/Molecules and Grams

• Since 6.02 X 1023 particles 1 mole AND1
  mole molar mass (grams)
• Can convert atoms/molecules to moles and then
  moles to grams! (2 step process)
• Cant go directly from atoms to grams!!!!
• MUST go thru MOLES.

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Calculations

• molar mass
  Avogadros number Grams
  Moles particles
• Everything must go through Moles!!!

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Atoms/Molecules and Grams

• How many atoms of Cu are 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
3.4 X 1023 atoms Cu
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Molar Conversions
molar mass
6.02 ? 1023
(g/mol)
(particles/mol)
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Make a Mole!
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Start Up

• How much do 3.8 x 1023 molecules of NH3 weigh?
• How many grams are needed to make 3.5 L of a 4 M
  solution of NaOH?
• Honors
• Given the equation 2 Na Cl2 ? 2 NaCl How many
  grams of NaCl is produced from 3.45 g of Na and
  excess Cl2.

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Molarity

• Molarity (M) is an expression of concentration
• M n ? number of moles
• V ? volume (in Liters)
• So 1.2M 1.2 mol
• 1L
• Example How many grams are in 3 L of a 1.5 M
  solution of NaOH?

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Review Chemical Equations

• Chemical change involves a reorganization of
• the atoms in one or more substances.

C2H5OH 3O2 2CO2 3H2O
reactants
products
When the equation is balanced it has quantitative
significance
1 mole of ethanol reacts with 3 moles of
oxygen to produce 2 moles of carbon dioxide and 3
moles of water
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Mole to Mole Ratio

• A balanced equation gives the recipe of moles
  for the reaction.
• 6Mg P4 ---gt 2Mg3P2
• 6 mol Mg required to produce 2 mol Mg3P2
• Ratio 6 mol Mg to 2 mol Mg3P2

or 6 mol Mg 2 mol Mg3P2
or 2 mol Mg3P2 6 mol Mg
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Stoichiometry
In solving a problem of this sort, the grand
thing is to be able to reason backward. This is a
very useful accomplishment, and a very easy one,
but people do not practice it much.
Sherlock Holmes, in Sir Arthur Conan Doyles A
Study in Scarlet

• Stoichiometry - The study of quantities of
  materials consumed and produced in chemical
  reactions.

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Calculating Masses of Reactants and Products

• Balance the equation.
• Convert mass to moles.
• Set up mole ratios.
• Use mole ratios to calculate moles of desired
  substance.
• Convert moles to grams, if necessary.

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Working a Stoichiometry Problem
6.50 grams of aluminum reacts with an excess of
oxygen. How many grams of aluminum oxide are
formed?
1. Identify reactants and products and write the
balanced equation.
Al

O2
4
3
Al2O3
2
a. Every reaction needs a yield sign!
b. What are the reactants?
c. What are the products?
d. What are the balanced coefficients?
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Working a Stoichiometry Problem
6.50 grams of aluminum reacts with an excess of
oxygen. How many grams of aluminum oxide are
formed?
4 Al 3 O2 ? 2Al2O3
6.50 g Al
1 mol Al
2 mol Al2O3
101.96 g Al2O3

? g Al2O3
4 mol Al
1 mol Al2O3
26.98 g Al
6.50 x 2 x 101.96 26.98 4
12.3 g Al2O3
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Start Up

• Use the balanced equation for the reaction of
  excess acetic acid with 275 g aluminum hydroxide
  to determine the mass of aluminum acetate
  theoretically produced.
• Honors 125 g of acetic acid reacts instead of
  excess. Determine limiting reagent first.
• 3 C2H3O2H Al(OH) 3 ? Al(C2H3O2) 3 3 H2O

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Limiting Reactant

• The limiting reactant is the reactant that is
  consumed first, limiting the amounts of products
  formed.

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Limiting Reagents - Combustion
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Start Up

• Write the empirical formula for the following
• C4H10
• P6015 (As a review, write the name of the
  empirical formula as well.)

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Steps to Stoichiometry with Limiting reactant

• Balance the equation.
• Convert masses to moles of product.
• Determine which reactant is limiting.
• Use moles of limiting reactant and mole ratios to
  find moles of desired product.
• Convert from moles to grams.

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Example

• Methyl alcohol, CH3OH, is a clean-burning, easily
  handled fuel. It can be made by the direct
  reaction of CO and H2.
• Assume you start with 12.0 g of H2 and 74.5 g of
  CO.
• CO H2? CH3OH
• a. Which of the reactants is the limiting
  reactant?
• 1. Balance Equation
• CO 2 H2? CH3OH
• 2. Convert both masses to moles of product
• 12.0 g H2 x 1 mol H2 x 1 mol CH3OH
• 2 g H2 2 mol H2
• 74.5 g CO x 1 mol_CO x 1 mol CH3OH
• 28 g CO 1 mol CO

3. Smallest number is limiting reagent.
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Use to find theoretical mass of product.

• Now that we know what is limiting, use CO to find
  the mass of CH3OH produced.
• 74.5 g CO x 1 mol_CO x 1 mol CH3OH x 32 g
  CH3OH
• 28 g CO 1 mol CO 1 mol
  CH3OH

Same as previous step, so could just multiply by
the molar mass of product.
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Percent Yield

• Experiments do not go perfectly.
• Determine the percent yield by this formula

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Calculating Percentage Composition
Example Calculate the percentage composition of
magnesium carbonate, MgCO3.
24.31 g 12.01 g 3(16.00 g) 84.32 g
100.00
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Formulas Review (dont write again)
Empirical formula the lowest whole number ratio
of atoms in a compound.
Molecular formula the true number of atoms of
each element in the formula of a compound.

• Examples
• molecular formula C6H6
• empirical formula CH

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Formulas Review (dont write again)
Formulas for ionic compounds are ALWAYS empirical
(lowest whole number ratio).
Examples
NaCl
MgCl2
Al2(SO4)3
K2CO3
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Formulas Review (dont write again)
Formulas for molecular compounds MIGHT be
empirical (lowest whole number ratio).
Molecular
C6H12O6
C12H22O11
H2O
Empirical
H2O
CH2O
C12H22O11
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Empirical Formula Determination

• Base calculation on 100 grams of compound.
• Determine moles of each element in 100 grams of
  compound.
• Divide each value of moles by the smallest of the
  values.
• Multiply each number by an integer to obtain all
  whole numbers.

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Empirical Formula Example
Adipic acid contains 49.32 C, 43.84 O, and
6.85 H by mass. What is the empirical formula of
adipic acid?
Just divide each number by the molar mass.
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Empirical Formula Determination
Divide each value of moles by the smallest of the
values.
Carbon
Hydrogen
Oxygen
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Empirical Formula Determination(part 3)
Multiply each number by an integer to get a whole
number.
Carbon 1.50
Hydrogen 2.50
Oxygen 1.00
x 2
x 2
x 2
3
5
2
C3H5O2
Empirical formula
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Finding the Molecular Formula
The empirical formula for adipic acid is C3H5O2.
The molecular mass of adipic acid is 146 g/mol.
What is the molecular formula of adipic acid?
1. Find the formula mass of C3H5O2
3(12.01 g) 5(1.01) 2(16.00) 73.08 g
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Finding the Molecular Formula
The empirical formula for adipic acid is C3H5O2.
The molecular mass of adipic acid is 146 g/mol.
What is the molecular formula of adipic acid?
2. Divide the molecular mass by the mass given by
the empirical formula.
3(12.01 g) 5(1.01) 2(16.00) 73.08 g
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Finding the Molecular Formula
The empirical formula for adipic acid is C3H5O2.
The molecular mass of adipic acid is 146 g/mol.
What is the molecular formula of adipic acid?
3. Multiply the empirical formula by this number
to get the molecular formula.
3(12.01 g) 5(1.01) 2(16.00) 73.08 g
(C3H5O2) x 2
C6H10O4
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Start Up

• Write the empirical formula for the following
• C4H10
• P6015 (As a review, write the name of the
  empirical formula as well.)

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Start Up

• Butyl acetate contains 62.07 C, 10.34 H, and
  27.59 O by mass. What is the empirical formula
  of butyl acetate?
• Based on the empirical formula you found, if the
  molecular mass is 116 g, what is the molecular
  formula of butyl acetate?

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Mole Activity!

• 2 Partners work together
• 2 activities
• Moles and Stoichiometry Lab
• By Golly By Molly Gum Lab
• Not formal labs, but activities for you to
  practice calculations and make the mole more
  tangible.

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Guidelines

• Before you start, decide which thing will have
  the most moles and write it down at the top of
  your paper.
• Everyone will need their own mole lab sheet to
  hand in
• 2 mole lab sheets, 1 gum data table, 1 set of gum
  questions

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Calculations

• of Nickel
• Since a nickel has 25 Ni, and 75 copper
• Mass of nickel (coin) x .25 Ni
• Sugar
• Use difference (mass of sugar)
• mass of pre-chewed gum
• Moles of Sugar
• Use difference (mass of sugar in grams) to find
  moles
• Calculate molar mass 1st using formula in lab

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Homework

• Percent Composition
• Optional worksheets
• Bookwork
• Any Questions?

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Review for Test

• Use Review sheet!

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Common Mistakes

• Forgetting to use Units!
• Calculator Issues
• Final Answer in Calculator Language or worse
• Rounding
• Not reading the question
• Identify what you know and what you are looking
  for.

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Review

• Mole Review for Test
• Core Content Terms
• All concepts/ideas behind problems
• Molar Mass
• Total mass of compound found using element masses
  from periodic table (written in g/mol)
• Percent Composition
• Individual element masses x number of elements
  by the molar mass x 100
• Grams to mole
• Write known from problem with units and use
  molar mass to convert
• Known g x 1 mol
• Molar Mass g ?from
  Periodic Table
• Moles to grams
• Write known from problem with units and use
  molar mass to convert
• Known moles x Molar Mass g ?from Periodic
  Table
• 1 mol

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• Moles to molecules /atoms
• Write known from problem with units and use
  Avogadros number to convert
• Known mol x NA molecules or atoms
• 1 mol
• Molecules/atoms to moles
• Write known from problem with units and use
  Avogadros number to convert
• Known molecules x 1 mol
• NA molecules or atoms
• Grams to molecules/atoms
• Write known from problem with units and use the
  molar mass and Avogadros (2 conversions)
• Known g x 1 mol x 1
  mol
• Molar Mass g NA molecules or
  atoms
• Molecules/atoms to grams
• Write known from problem with units and use the
  molar mass and Avogadros (2 conversions)
• Known molecules x 1 mol x
  Molar Mass g
• NA molecules
  1 mol

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• Mole Ratio/Stoichiometry
• Use the coefficients to determine the mole ratios
  between compounds and use as conv. factor
• Known g x 1 mol x mol product
• Molar Mass g mol given
• Limiting Reagent
• Same as above, but do twice (use each mass), then
  use smallest and convert to moles of product.
• Empirical /Molecular Formula
• Reduce the molecular formula to the simplest
  whole number ratio
• ?To find empirical from Comp Work Backward 1)
  --gt g, 2) divide by molar mass, 3) divide by
  smallest , 3) if not whole numbers, multiply by
  an integer to make a whole number. These are the
  subscripts for formula.
• ?To find molecular from empirical, divide given
  molecular mass by empirical mass. X each
  subscript by this.

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SourcesThanks!

• Kristen Olson
• www.hse.k12.in.us/staff/kbowen/Assignments/Steps2
  0to20balancing20Chemical20equations.pdf
• http//www.usoe.org/curr/science/sciber00/8th/matt
  er/sciber/chemtype.htm