CHE 111 - Module 4

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CHE 111 - Module 4
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• CHAPTER 4 5
• LECTURE NOTES

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Stoichiometry Balancing Equations
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• Remember we stated in the previous chapter that
  stoichiometry is the study of the quantitative
  relationships between the amounts of reactants
  and products in chemical reactions.
• We use BALANCED equations to understand
  stoichiometric relationships of the elements and
  compounds within a chemical reaction.

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The Balanced Equation
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• 2Al(s) 3Br2(l) ? Al2Br6(s)
• 2mol of Al 3mol of Br2 1mol of Al2Br6
• 2 atoms of Al 2 atoms of Al
• 6 atoms of Br 6 atoms of Br
• The number of the same atom of each element
  must be equal on each side of the equation.

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A Closer Look at the Equation
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• 2Al(s) 3Br2(l) ? Al2Br6(s)
• The chemicals on the left are the reactants and
  the right are the products.
• The coefficient in front of the chemical denotes
  the stoichiometric relationship.
• The numerical subscript represents the number of
  atoms present in the molecule.
• The letter subscripted denotes the phase of
  matter.

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Balancing Equations
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• For example the following is balanced.
• CH4 2O2 ? CO2 2H2O
• Try to balance the following
• Fe2S3 O2 ? Fe2O3 S
• Al H2SO4 ? Al2(SO4)3 H2
• Ca Al2Br6 ? CaBr2 Al

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Balanced Equations

• Check your answer from the previous slide
• 2Fe2S3 3O2 ? 2Fe2O3 6S
• 2Al 3H2SO4 ? Al2(SO4)3 3H2
• 3Ca Al2Br6 ? 3CaBr2 2Al

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Types of Reactions
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• Combination Reactions
• Decomposition Reactions
• Displacement (Single-Replacement) Reactions
• Metathesis (Double-Replacement) Reactions
• Combustion Reactions

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Combination Reactions
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• A combination reaction is a reaction where two
  substances chemically combine to form another
  substance.
• A B ? AB
• 2Na(s) Cl2(g) ? 2NaCl(s)
• P4(s) 6Cl2(g) ? 4PCl3(s)

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Decomposition Reaction
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• A decomposition reaction is when a single
  compound decomposes into two or more other
  substances.
• AB ? A B
• 2KClO3(s) ? 2KCl(s) 3O2(g)
• 2NO2(g) ? 2NO(g) O2(g)

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Displacement Reaction
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• A displacement (single replacement) reaction is a
  reaction where one element displaces another
  element.
• A BC ? B AC
• Zn(s) 2HCl(aq) ? ZnCl2(aq) H2(g)
• Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq) 2Ag(s)

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Metathesis Reaction
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• A metathesis (double replacement) reaction is a
  reaction where two compounds switch cations to
  form two new compounds.
• AB- CD- ? AD- CB-
• CaCl2(aq) Na2CO3(aq) ? CaCO3(s) 2NaCl(aq)
• AgNO3(aq) KCl(aq) ? ???

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SOLUBILITY
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• Solubility the amount of a substance that can
  be dissolved in a given quantity of solvent (like
  water) at a specific temperature
• Unsaturated amount of substance less than
  saturated
• Saturated the exact amount at solubility
• Supersaturated excess amount of substance

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How Solubility Influences Rxn
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• When a substance is soluble in water, it will
  appear with a subscript of (aq) meaning that the
  substance is broken up into its ions
  incorporated into the water lattice.
• When a substance is insoluble in water, it will
  be written with a subscript of (s), (l), or (g)
  and will precipitate out of solution.

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Solubility of Ionic Compounds in Water
Soluble Compounds Exceptions
Sodium, potassium, and ammonium compounds
Acetates and nitrates
Halides (chlorides, bromides, Lead(II), silver, and mercury (I) and iodides) halides are insoluble
Sulfates Calcium, strontium, barium, and Lead(II) sulfates are insoluble
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Insolubility of Ionic Compounds in Water
Insoluble Compounds Exceptions
Carbonates and phosphates Sodium, potassium, and ammonium compounds are soluble.
Hydroxides Sodium, potassium, calcium, strontium, and barium compounds are soluble
Sulfide Sodium, potassium, calcium, and ammonium compounds are soluble
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A Look at Metathesis Again
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• Looking back at slide 10 to the first reaction
  when the cations rearranged, the CaCO3 being
  insoluble by our definition is recorded as CaCO3
  (s). The CaCO3 would precipitate out of solution
  as a solid.
• Looking at AgNO3(aq) KCl(aq) ? ?, we can
  rearrange the cations and conclude that the AgCl
  is a solid and will precipitate out of solution

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Types of Metathesis Reactions
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• Three classifications of metathesis reactions
• Precipitation reaction - formation of a solid
• Pb(NO3)2(aq) Na2CO3(aq) ? PbCO3(s) 2NaNO3(aq)
  
• Neutralization reaction - formation of water
• HCl(aq) NaOH(aq) ? NaCl(aq) H2O(l)
• Gas formation reaction - CO2, H2S, SOx, NOx are
  typically formed

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Precipitation Reactions
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• A solid precipitate is produced in the
  rearrangement of cations as follows
• Pb(NO3)2(aq) Na2CO3(aq) ? PbCO3(s)
  2NaNO3(aq)
• The Ionic Equation is expressed as
• Pb2 2NO3- 2Na CO3-2 ? PbCO3(s)
  2Na 2NO3-
• After neglecting the spectator ions, the net
  ionic equation will look like
• Pb2(aq) CO3-2(aq) ? PbCO3(s)

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Reviewing Ionic Compounds
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• Ca2 2Cl- ? CaCl2
• Each ion comes together based on charge to
  form an overall neutral ionic compound.
• 3Ca2 2PO4-3 ? Ca3(PO4)2
• The cation and the polyatomic ion come
  together based on charge to form an overall
  neutral ionic compound.

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Net Ionic Equations (NIE)
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• If you were given the reactants Ca(NO3)2 and
  Na3PO4 you should be able to predict the
  precipitate and write a balance equation, the
  ionic equation, and the net ionic equation (NIE)
  for this reaction.
• The NIE for these reactants is as follows
• 3Ca2(aq) 2PO4-3(aq) ? Ca3(PO4)2(s)

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Common Polyatomic Ions
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• carbonate ion CO3-2
• sulfate ion SO4-2
• sulfite ion SO3-2
• hydroxide OH-
• phosphate PO4-3
• permanganate MnO4-
• chromate CrO4-2
• dichromate Cr2O7-2

• ammonium NH4
• oxalate C2O4-2
• bicarbonate HCO3-
• cyanide ion CN-
• acetate C2H3O3-

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Neutralization Reaction
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• A neutralization reaction is a reaction that
  occurs between an acid and a base with the
  production of a salt and water.
• HCl(aq) NaOH(aq) ? NaCl(aq) H2O(l)
• acid base salt
  water

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Gas Formation Reaction
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• A gas formation reaction is a metathesis reaction
  that generates a gas as a product.
• Metal carbonates or bicarbonates acid
• Metal sulfides acid
• Metal sulfites acid
• Ammonium salts and strong base

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Metal Carbonates
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• Metal carbonates or bicarbonates when combined
  with an acid form salt, water and carbon dioxide
  gas.
• Na2CO3(aq) 2HCl(aq) ? 2NaCl(aq) H2O(l)
  CO2(g)
• Where CO2 gas is given off

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Metal Sulfides
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• Metal sulfides when combined with an acid form
  salt and hydrogen sulfide gas.
• Na2S(aq) 2HCl(aq) ? 2NaCl(aq) H2S(g)
• Where H2S gas is given off

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Metal Sulfites
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• Metal sulfites when combined with an acid form
  salt, water, and sulfur dioxide gas.
• Na2SO3(aq) 2HCl(aq) ? 2NaCl(aq) H2O(l)
  SO2(g)
• Where SO2 gas is given off

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Ammonium Salts
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• Ammonium salts when combined with a base produce
  salt, water and ammonia.
• NH4Cl (aq) NaOH(aq) ? NaCl(aq) H2O(l) NH3(g)
• Where ammonia gas is given off

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Combustion Reactions
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• A combustion reaction is a reaction with
  molecular oxygen to form products in which all
  elements are combined with oxygen.
• CH4 2O2 ? CO2 2H2O

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Limiting Reactants
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• One of the reactants is in limited supply and
  thus restricts the amount of product formed.
• Think of it as If you wanted to bake a batch of
  peanut butter cookies and the recipe calls for 1
  cup of peanut butter and all you have is ½ a cup,
  even though you have all the other ingredients,
  you can at most make ½ a batch of cookies.

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Limiting Reactants (cont.)
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• Consider the combustion reaction
• CH4 2O2 ? CO2 2H2O
• How much CO2 can be produced if you have 0.13g of
  methane and 0.45g of O2?

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Percent Yield
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• The maximum amount of product that can be
  obtained from a chemical reaction is the
  theoretical yield.
• The actual amount produced in a chemical process
  is the actual yield.
• The percent yield is equal to the actual yield
  divided by the theoretical yield times 100.

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Redox Reactions
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• Oxidation of an element takes place when
  electrons are lost from the valence shell of the
  element.
• Reduction of an element takes place when
  electrons are added to the valence shell of the
  element.
• Redox reactions show the transfer of electrons
  that takes place during oxidation and reduction.

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Redox Reactions (cont.)
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• All oxidation and reduction reactions involve
  transfer of electrons between substances.
• View CD-ROM screen 5.12
• Ag accepts electrons for Cu and is reduced to Ag
  and Cu loses electrons to Ag and is oxidized to
  Cu2 in the following redox rxn
• 2Ag(aq) Cu(s) ? 2Ag(s) Cu2(aq)

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Redox Reactions (cont.)
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• The oxidation half reaction is
• Cu(s) 2e- ? Cu2(aq)
• The reduction half reaction is
• 2Ag(aq) 2e- ? 2Ag(s)
• Cu is called the reducing agent because it caused
  Ag to be reduced and Ag is called the
  oxidizing agent because it caused Cu to be
  oxidized.

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Determining Oxidation Numbers
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• Each atom in a pure element has an oxidation
  number of zero.
• For monoatomic ions, the ox. number is equal to
  its ionic charge.
• F is always 1, other halogens are 1 as well
  except with oxygen or fluorine.
• The ox. number for H is 1 except with hydrides
  (CaH2).and O is 2 except with peroxides (H2O2).
• The ? ox. must 0 for a compound or to the
  overall charge of polyatomic ion being considered.

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Balancing Redox Reactions
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• We can use the balance of electrons transferred
  in a redox reaction to help us balance the
  overall equation.
• Consider the unbalanced equation
• Zn(s) HCl(aq) ? ZnCl2(aq) H2(g)
• The balanced equation takes into consideration
  the oxidation of the Zn and the reduction of the
  H.

Zn(s) 2HCl(aq) ? ZnCl2(aq) H2(g)
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Molarity
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• Molarity Moles of Solute
• Liters of Total Solution
• Symbol for molarity is M
• Units are moles/Liter

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Solution Preparation

• To prepare a 1.0M solution of NaCl, you would
  determine how many grams of NaCl is contained in
  1.0 moles of NaCl and then dissolve that amount
  in a 1.0L volumetric flask. You would then qs
  with distilled H2O.
• 1.0M NaCl 1 mole (or 58.44g) NaCl
• 1.0L of solution
• How much NaCl would you use to make a 0.1M
  solution of NaCl?

As 1/10 of a mole 5.844g NaCl, you would
dissolve 0.1mole (5.844g) of NaCl in 1.0L of
solution.
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Acids

• An acid is defined as follows
• Arrhenius releases H when dissolved in H2O
• Bronsted-Lowrey a substance that can donate a
  proton to another substance
• Lewis a substance that can accept a pair of
  electrons from another atom to form a new bond

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Bases

• A base is defined as follows
• Arrhenius releases OH- when dissolved in H2O
• Bronsted-Lowrey a substance that can accept a
  proton from another substance
• Lewis a substance that can donate a pair of
  electrons to another atom to form a new bond

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pH and Concentrations of Acids and Bases

• pH -log H
• 1 acidic 7 basic 14
• When dealing with H less than 0.1M (pH1),
  we use activity coefficients instead of pH.

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pH of Household Items

• pH of vinegar 2.80
• pH of soda 2.90
• pH of orange juice 3.80
• pH of pure water 7.00
• pH of blood 7.40
• pH of ammonia 11.00
• pH of oven cleaner 11.7

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Titration

• A method for quantitative analysis of a substance
  by essentially complete reaction in solution with
  a measured quantity of a reagent of known
  concentration.
• Often used in redox reactions
• Many redox reactions go rapidly to completion in
  aqueous media to determine the equivalency point.
• Typically used for neutralization reactions.
• Acid is titrated with a base using an indicator
  to determine the equivalency point of the
  neutralization reactions.

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