ch07 final
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John E. McMurry Robert C. Fay
Lecture NotesAlan D. EarhartSoutheast Community College Lincoln, NE
General Chemistry: Atoms First
Chapter 7Reactions in Aqueous Solution
Copyright 2010 Pearson Prentice Hall, Inc.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/2
Some Ways That Chemical
Reactions Occur
Precipitation Reactions: Processes in which soluble
ionic reactants yield an insoluble solid product that
falls out of solution.
2KNO3(aq) + PbI
2(s)Pb(NO3)2(aq) + 2KI(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/3
Some Ways That Chemical
Reactions Occur
Acid-Base Neutralization Reactions: Processes in
which an acid reacts with a base to yield water plus an
ionic compound called a salt.
H2O(l) + NaCl(aq)HCl(aq) + NaOH(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/4
Some Ways That Chemical
Reactions Occur
Oxidation-Reduction (Redox) Reactions: Processes
in which one or more electrons are transferred
between reaction partners (atoms, molecules, or ions).
MgCl2(aq) + H2(g)Mg(s
) + 2HCl(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/5
Electrolytes in Aqueous
Solution
Electrolytes: Substances which dissolve in water to
produce conducting solutions of ions.H2O
Na1+(aq) + Cl1-(aq)NaCl(s)
Nonelectrolytes: Substances which do not produce
ions in aqueous solutions.H2O
C12H22O11(aq)C12H22O11(s)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/7
Electrolytes in Aqueous
Solution
Weak Electrolytes: Compounds that dissociate to a
smallextent into ions when dissolved in water.
H1+
(aq) + CH3CO21-
(aq)CH3CO2H(aq)
Strong Electrolytes: Compounds that dissociate to a
large extent into ions when dissolved in water.
H1+(aq) + Cl1-(aq)HCl(g)H2O
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Electrolytes in Aqueous
Solution
StrongAcids: hydrochloric acid, hydrobromic acid,
hydroiodic acid, perchloric acid, nitric acid, sulfuric acid.
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Electrolytes in Aqueous
Solution
Ionic compounds
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/10
Electrolytes in Aqueous
Solution
Weakacids
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Chapter 7/11
Electrolytes in Aqueous
Solution
Molecular compounds (other than any strong or weak
electrolytes)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/12
Electrolytes in Aqueous
Solution
Dissociation Equations
Fe3+
(aq) + 3Br1-
(aq)FeBr3(s
)
H2O
2Na1+
(aq) + SO42-
(aq)Na2SO4(s)
H2O
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/13
Aqueous Reactions and Net
Ionic Equations
2KNO3(aq) + PbI2(s)Pb(NO3)2(aq) + 2KI(aq)
MolecularEquation: All substances in the chemical
equation are written using their complete formulas as
if they were molecules.
strong electrolytes precipitate
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/14
Aqueous Reactions and Net
Ionic Equations
Ionic Equation: All of the strong electrolytes are
written as ions.
2K1+(aq) + 2NO31- (aq) + PbI2(s)
Pb2+(aq) + 2NO31- (aq) + 2K1+(aq) + 2I1-(aq)
2KNO3(aq)
Pb(NO3)2(aq) 2KI(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/15
Aqueous Reactions and Net
Ionic Equations
Spectator Ions: Ions that undergo no change during
the reaction and appear on both sides of the reaction
arrow.
2K1+(aq) + 2NO31- (aq) + PbI2(s)
Pb2+(aq) + 2NO31- (aq) + 2K1+(aq) + 2I1-(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/16
Aqueous Reactions and Net
Ionic Equations
PbI2(s)Pb2+(aq) + 2I1-(aq)
Net Ionic Equation: Only the ions undergoing change
are shown.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/17
Precipitation Reactions and
Solubility Guidelines
Solubility: States how much of a compound will
dissolve in a given amount of solvent at a given
temperature.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/18
Precipitation Reactions and
Solubility Guidelines
1. A compound is probably soluble if it contains one of
the following cations:
Group 1A cation: Li1+, Na1+, K1+, Cs1+
Ammonium ion: NH41+
2. A compound is probably soluble if it contains one of
the following anions:
Halide: Cl1-, Br1-, I1-
exceptAg1+
, Hg22+
, and Pb2+
compounds Nitrate (NO3
1-), perchlorate (ClO41-), acetate (CH3CO2
1-),
sulfate (SO42-)
exceptBa2+, Hg22+, and Pb2+ sulfates
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/19
Precipitation Reactions and
Solubility Guidelines
Write the molecular, ionic, and net ionic equations for
the reaction that occurs when aqueous solutions of
AgNO3 and Na2CO3 are mixed.
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Chapter 7/20
Precipitation Reactions and
Solubility Guidelines
Write the chemical formulas of the products (useproper ionic rules).
Ag2CO3AgNO3(aq) + Na2CO3(aq) + NaNO3
CB +ADAB + CD
double replacement reaction
Write the molecular, ionic, and net ionic equations for
the reaction that occurs when aqueous solutions of
AgNO3 and Na2CO3 are mixed.
1.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/21
Precipitation Reactions and
Solubility Guidelines
MolecularEquation: Balance the equation andpredict the solubility of each possible product.
Ag2CO3(s) + 2NaNO3(aq)2AgNO3(aq) + Na2CO3(aq)
Contains a group 1A cation.
Neither the cation nor the
anion is in the solubility list.
Write the molecular, ionic, and net ionic equations for
the reaction that occurs when aqueous solutions of
AgNO3 and Na2CO3 are mixed.
2.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/22
Precipitation Reactions and
Solubility Guidelines
Ionic Equation: Dissociate the soluble ioniccompounds.
Write the molecular, ionic, and net ionic equations for
the reaction that occurs when aqueous solutions of
AgNO3 and Na2CO3 are mixed.
3.
Ag2CO3(s) + 2Na1+(aq) + 2NO3
1-(aq)
2Ag1+
(aq) + 2NO31-
(aq) + 2Na1+
(aq) + CO32-
(aq)
2NaNO3(aq)
2AgNO3(aq) Na2CO3(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/23
Precipitation Reactions and
Solubility Guidelines
Write the molecular, ionic, and net ionic equations for
the reaction that occurs when aqueous solutions of
AgNO3 and Na2CO3 are mixed.
Net Ionic Equation: Eliminate the spectator ions fromthe ionic equation.
Ag2CO3(s)2Ag1+(aq) + CO3
2-(aq)
4.
Ag2CO3(s) + 2Na1+
(aq) + 2NO31-
(aq)
2Ag1+(aq) + 2NO31- (aq) + 2Na1+(aq) + CO3
2-(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/24
Acids, Bases, and
Neutralization Reactions
H3O1+(aq) + Cl1-(aq)HCl(aq) + H2O(aq)
Acid (Arrhenius): A substance that dissociates in
water to produce hydrogen ions, H1+:
H1+(aq) + A1-(aq)HA(aq)
In water, acids produce hydronium ions, H3O1+:
H1+(aq) + Cl1-(aq)HCl(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/25
Acids, Bases, and
Neutralization Reactions
Ammonia, commonly called ammonium hydroxide is
a base:
M1+(aq) + OH1-(aq)MOH(aq)
Na1+(aq) + OH1-(aq)NaOH(aq)
Base (Arrhenius): A substance that dissociates in
water to produce hydroxide ions, OH1-:
NH41+(aq) + OH1-(aq)NH3(aq) + H2O(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/26
Acids, Bases, and
Neutralization Reactions
Weak acids and weak bases are weak electrolytes.
Strong acids and strong bases are strong electrolytes.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/27
ateic
iteous
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/28
Acids, Bases, and
Neutralization ReactionsBinary Acids
HCl hydrochloric acid
HBr hydrobromic acid
HF hydrofluoric acid
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Acids, Bases, and
Neutralization Reactions
MA + H2OHA + MOH
These acid-base neutralization reactions are double-
replacement reactions just like the precipitation
reactions:
or
MA + HOHHA + MOH
WaterAcid Base Salt
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/30
Write the chemical formulas of the products (use
proper ionic rules for the salt).
1.
Acids, Bases, and
Neutralization Reactions
Write the molecular, ionic, and net ionic equations for
the reaction of aqueous HBr and aqueous Ba(OH)2.
H2OHBr(aq) + Ba(OH)2(aq) + BaBr2
SaltAcid Base Water
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/31
MolecularEquation: Balance the equation and
predict the solubility of the salt in the products.
2.
Acids, Bases, and
Neutralization Reactions
Write the molecular, ionic, and net ionic equations for
the reaction of aqueous HBr and aqueous Ba(OH)2.
2H2O(l) + BaBr2(aq)2HBr(aq) + Ba(OH)2(aq)
Use the solubility rules.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/32
Ionic Equation: Dissociate a strong acid and the
soluble ionic compounds.
3.
Acids, Bases, and
Neutralization Reactions
Write the molecular, ionic, and net ionic equations for
the reaction of aqueous HBr and aqueous Ba(OH)2.
2H2O(l) + Ba2+(aq) + 2Br1-(aq)
2H1+(aq) + 2Br1-(aq) + Ba2+(aq) + 2OH1-(aq)
BaBr2(aq)
2HBr(aq) Ba(OH)2(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/33
2H2O(l) + Ba2+(aq) + 2Br1-(aq)
Acids, Bases, and
Neutralization Reactions
Write the molecular, ionic, and net ionic equations for
the reaction of aqueous HBr and aqueous Ba(OH)2.
Net Ionic Equation: Eliminate the spectator ions from
the ionic equation.
4.
2H1+(aq) + 2Br1-(aq) + Ba2+(aq) + 2OH1-(aq)
or
H2O(l)H1+(aq) + OH1-(aq)
2H2O(l)2H1+(aq) + 2OH1-(aq)
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Acids, Bases, and
Neutralization Reactions
Write the molecular, ionic, and net ionic equations for
the reaction of aqueous NaOH and aqueous HF.
Write the chemical formulas of the products (use
proper ionic rules for the salt).
1.
SaltAcid Base Water
H2OHF(aq) + NaOH(aq) + NaF
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Acids, Bases, and
Neutralization Reactions
Write the molecular, ionic, and net ionic equations for
the reaction of aqueous NaOH and aqueous HF.
MolecularEquation: Balance the equation and
predict the solubility of the salt in the products.
2.
H2O(l) + NaF(aq)HF(aq) + NaOH(aq)
Use the solubility rules.
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Acids, Bases, and
Neutralization Reactions
Write the molecular, ionic, and net ionic equations for
the reaction of aqueous NaOH and aqueous HF.
Ionic Equation: Dissociate a strongacid and the
soluble ionic compounds.
3.
H2O(l) + Na1+(aq) + F1-(aq)HF(aq) + Na1+(aq) + OH1-(aq)
NaF(aq)
NaOH(aq)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/37
Acids, Bases, and
Neutralization Reactions
Write the molecular, ionic, and net ionic equations for
the reaction of aqueous NaOH and aqueous HF.
Net Ionic Equation: Eliminate the spectator ions from
the ionic equation.
4.
H2O(l) + Na1+(aq) + F1-(aq)HF(aq) + Na1+(aq) + OH1-(aq)
H2O(l) + F1-(aq)HF(aq) + OH1-(aq)
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Chapter 7/38
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/39
Oxidation-Reduction (Redox)
Reactions
2Fe2O3(s)4Fe(s) + 3O2(g)Rusting of iron:
an oxidation of Fe
4Fe(s) + 3CO2(g)2Fe2O3(s) + 3C(s)Manufacture of iron:
a reduction of Fe
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/40
Oxidation-Reduction (Redox)
Reactions
Oxidation: The loss of one or more electrons by a
substance, whether element, compound, or ion.
Reduction: The gain of one or more electrons by a
substance, whether element, compound, or ion.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/41
Oxidation-Reduction (Redox)
Reactions
1. An atom in its elemental state has an oxidation
number of 0.
Rules for Assigning Oxidation Numbers
Oxidation Number (State): A value which indicates
whether an atom is neutral, electron-rich, or electron-
poor.
Na H2 Br2 S Ne
Oxidation number 0
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/42
Oxidation-Reduction (Redox)
Reactions
2. An atom in a monatomic ion has an oxidation
number identical to its charge.
Na1+
+1
Ca2+
+2
Al3+
+3
Cl1-
-1
O2-
-2
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Oxidation-Reduction (Redox)
Reactions
b) Oxygen usuallyhas an oxidation number of -2.
H O1-
-2+1
HH Ca
-1-1 +2
3. An atom in a polyatomic ion or in a molecular
compound usually has the same oxidation number
it would have if it were a monatomic ion.
a) Hydrogen can be either +1 or -1.
OH O
-1+1 -1
HH O
+1+1 -2
H
+1
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Oxidation-Reduction (Redox)
Reactions
H Cl
+1 -1
c) Halogens usuallyhave an oxidation number of -1.3.
ClCl O
+1+1 -2
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Oxidation-Reduction (Redox)
Reactions
Cr2O72-
-2+1 x
4. The sum of the oxidation numbers is 0 for a neutral
compound and is equal to the net charge for a
polyatomic ion.
x = +6
2(x) + 7(-2) = -2 (net charge)
H2SO3
x -2
x = +4
2(+1) + x + 3(-2) = 0 (net charge)
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Identifying Redox Reactions
Causes oxidation
Gains one or more electrons Undergoes reduction
Oxidation number of atom decreases
Causes reduction
Loses one or more electrons
Undergoes oxidation
Oxidation number of atom increases
Oxidizing Agent
Reducing Agent
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Identifying Redox Reactions
2Fe23O2(g)+4Fe(s) O3(s)
-20
reduction
oxidation
+30
Oxidizing Agent
Reducing Agent
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3
Identifying Redox Reactions
4Fe(s)C(s) +2Fe2O3 + 3 (g)(s) O2C
oxidation
+40
-2+3
reductionOxidizing Agent
Reducing Agent
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/49
The Activity Series of the
Elements
2Ag1+(aq) + Cu(s)2Ag(s) + Cu2+(g)
Cu2+(aq) + 2Ag(s)Cu(s) + 2Ag1+(g)
Which one of these reactions will occur?
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Chapter 7/50
The Activity Series of the
Elements
The elements that are
higher up in the table
are more likely to be
oxidized.
Thus, any element
higher in the activity
series will reduce theion of any element
lower in the activity
series.
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Balancing Redox Reactions:
The Half-Reaction Method
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Balancing Redox Reactions:
The Half-Reaction Method
Balance the following net ionic equation in acidic
solution:
Cr3+(aq) + IO31-(aq)I1-(aq) + Cr2O7
2-(aq)
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Balancing Redox Reactions:
The Half-Reaction Method
Write the two unbalanced half-reactions.
IO31-(aq)I1-(aq)
Cr3+(aq)Cr2O72-(aq)
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Balancing Redox Reactions:
The Half-Reaction Method
Multiply each half-reaction by a factor to make the
electron count the same in both half-reactions.
IO31-(aq) + 6H1+(aq)6e- + 3H2O(l) + I
1-(aq)
2Cr3+(aq) + 7H2O(l) + 6e-14H1+(aq) + Cr2O7
2-(aq)
oxidation:
reduction:
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Balancing Redox Reactions:
The Half-Reaction Method
Add the two balanced half-reactions together and
cancel species that appear on both sides of the
equation.
IO31-(aq) + 6H1+(aq)6e- + 3H2O(l) + I
1-(aq)
2Cr3+(aq) + 7H2O(l) + 6e-14H1+(aq) + Cr2O7
2-(aq)
oxidation:
reduction:
IO31-(aq) + 2Cr3+(aq) + 4H2O(l)
8H1+(aq) + I1-(aq) + Cr2O72-(aq)
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MnO2(s) + BrO31-(aq)MnO4
1-(aq) + Br1-(aq)
Balancing Redox Reactions:
The Half-Reaction Method
Balance the following net ionic equation in basic
solution:
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Balancing Redox Reactions:
The Half-Reaction Method
Write the two unbalanced half-reactions.
BrO31-(aq)Br1-(aq)
MnO2(s)MnO41-(aq)
B l i R d R i
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Balancing Redox Reactions:
The Half-Reaction Method
Balance both half-reactions for all atoms except O and
H.
BrO31-(aq)Br1-(aq)
MnO2(s)MnO41-(aq)
B l i R d R ti
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Balancing Redox Reactions:
The Half-Reaction Method
BrO31-(aq) + 6H1+(aq)3H2O(l) + Br
1-(aq)
MnO2(s) + 2H2O(l)4H1+(aq) + MnO4
1-(aq)
Balance each half-reaction for O by adding H2O, and
then balance for H by adding H1+.
B l i R d R ti
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Balancing Redox Reactions:
The Half-Reaction Method
BrO31-(aq) + 6H1+(aq) + 6e-3H2O(l) + Br
1-(aq)
MnO2(s) + 2H2O(l)3e- + 4H1+(aq) + MnO4
1-(aq)
Balance each half-reaction for charge by adding
electrons to the side with greater positive charge.
B l i R d R ti
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Balancing Redox Reactions:
The Half-Reaction Method
Multiply each half-reaction by a factor to make the
electron count the same in both half-reactions.
2
BrO31-(aq) + 6H1+(aq) + 6e-3H2O(l) + Br
1-(aq)
MnO2(s) + 2H2O(l)3e- + 4H1+(aq) + MnO4
1-(aq)
B l i R d R ti
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2MnO2(s) + H2O(l) + BrO31-(aq)
2H1+(aq) + 2MnO41-(aq) + Br1-(aq)
Balancing Redox Reactions:
The Half-Reaction Method
BrO31-(aq) + 6H1+(aq) + 6e-3H2O(l) + Br
1-(aq)
2MnO2(s) + 4H2O(l)6e- + 8H1+(aq) + 2MnO4
1-(aq)
Add the two balanced half-reactions together and
cancel species that appear on both sides of the
equation.
B l i R d R ti
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Balancing Redox Reactions:
The Half-Reaction Method
Since the reaction occurs in a basic solution,
neutralize the excess H1+ by adding OH1- and cancel
any water (if possible).
2MnO2(s) + H2O(l) + BrO31-(aq) + 2OH1-(aq)
2OH1-(aq) + 2H1+(aq) + 2MnO41-(aq) + Br1-(aq)
2H2O
2MnO2(s) + BrO31-(aq) + 2OH1-(aq)
H2O(l) + 2MnO41-(aq) + Br1-(aq)
R d St i hi t
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Redox Stoichiometry
Titration: A procedure for determining the concentration
of a solution by allowing a carefully measured volume to
react with a solution of another substance (the standard
solution) whose concentration is known.
5H2C2O4(aq) + 2MnO41-(aq) + 6H1+(aq)
10CO2(g) + 2Mn2+(aq) + 8H2O(l)
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Chapter 7/66
R d St i hi t
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Redox Stoichiometry
5H2C2O4(aq) + 2MnO41-(aq) + 6H1+(aq)
10CO2(g) + 2Mn2+(aq) + 8H2O(l)
A solution is prepared with 0.2585 g of oxalic acid,
H2C2O4. 22.35 mL of an unknown solution of potassium
permanganate are needed to titrate the solution. What is
the concentration of the potassium permanganate
solution?
Moles ofH2C2O4Mass ofH2C2O4
Moles ofKMnO4Molarity ofKMnO4
Mole Ratio Molarity of
KMnO4
Molar Mass
of H2C2O4
R d St i hi t
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Redox Stoichiometry
5H2C2O4(aq) + 2MnO41-(aq) + 6H1+(aq)
10CO2(g) + 2Mn2+(aq) + 8H2O(l)
Moles of H2C2O4 available:
90.04 g
1 mol= 0.002871 mol H2C2O4
0.2585 g H2C2O4
Moles of KMnO4 reacted:
5 mol H2C2O4
2 mol KMnO4= 0.001148 mol KMnO4
0.002871 mol H2C2O4
x
x
Redo Stoichiometr
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1 L
1000 mL
Redox Stoichiometry
5H2C2O4(aq) + 2MnO41-(aq) + 6H1+(aq)
10CO2(g) + 2Mn2+(aq) + 8H2O(l)
Concentration of KMnO4 solution:
= 0.05136 M KMnO422.35 mL
x0.001148 mol KMnO4