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GENERAL CHEMISTRY
Principles and Modern Applications
PETRUCCI
HERRING
MADURA
TENTH EDITION
BISSONNETTE
Introduction to Reactions
in Aqueous Solutions
5
PHILIP DUTTON
UNIVERSITY OF WINDSOR
DEPARTMENT OF CHEMISTRY AND
BIOCHEMISTRY
Slide 1 of 43
General Chemistry: Chapter 5
Copyright © 2011 Pearson Canada Inc.
Introduction to Reactions
in Aqueous Solutions
Slide 2 of 43
CONTENTS
6-1
The Nature of Aqueous Solutions
6-2
Precipitation Reactions
6-3
Acid–Base Reactions
6-4
Oxidation–Reduction Reactions:
Some General Principles
6-5
Balancing Oxidation–Reduction
Equations
6-6
Oxidizing and Reducing Agents
6-7
Stoichiometry of Reactions in
Aqueous Solutions: Titrations
General Chemistry: Chapter 5
Copyright © 2011 Pearson Canada Inc.
5.1 The Nature of Aqueous Solutions
Water
• Inexpensive
• Can dissolve a vast number of substances
• Many substances dissociate into ions
Aqueous solutions are found everywhere
• Seawater
• Living systems
Slide 3 of 43
General Chemistry: Chapter 5
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5.1 The Nature of Aqueous Solutions
Strong electrolyte is completely ionized.
Good electrical conduction.
Weak electrolyte only partially ionizes.
Fair conductor of electricity.
Non-electrolyte does not dissociate.
Poor conductor of electricity.
Slide 4 of 43
General Chemistry: Chapter 5
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5-5
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FIGURE 5-2
Conduction of electricity through a solution
Slide 6 of 43
General Chemistry: Chapter 5
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Figure 5-4
Three Types of Electrolytes
Slide 7 of 43
General Chemistry: Chapter 5
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 Essentially all soluble ionic compounds and only a relatively few
molecular compounds are strong electrolytes.
 Most molecular compounds are either nonelectrolytes or weak
electrolytes.
A strong electrolyte:
MgCl2(s) → Mg2+(aq) + 2 Cl-(aq)
A weak electrolyte:
→ CH3CO2-(aq) + H+(aq)
CH3CO2H(aq) ←
A non-electrolyte:
CH3OH(aq)
Slide 8 of 43
General Chemistry: Chapter 5
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Figure 5-5
The hydrated proton
Slide 9 of 43
General Chemistry: Chapter 5
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Relative Concentrations in Solution
MgCl2(s) → Mg2+(aq) + 2 Cl-(aq)
In 0.0050 M MgCl2:
Stoichiometry is important.
[Mg2+] = 0.0050 M
Slide 10 of 43
[Cl-] = 0.0100 M
General Chemistry: Chapter 5
[MgCl2] = 0 M
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5 - 11
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5-2 Precipitation Reactions
• NaCl is soluble in water but AgCl is
insoluble
• Soluble ions can combine to form an
insoluble compound. The rex is called
precipitation rex
• A test for the presence of chloride ion in
water.
Ag+(aq) + Cl-(aq) → AgCl(s)
Figure 5-6
Qualitative test for Cl- in tap water
Add AgNO3 to NaCl,
Slide 12 of 43
AgCl will be precipitated
General Chemistry: Chapter 5
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Predicting Precipitation Reactions
AgNO3(aq)
Figure 5-7
A precipitate of silver iodide
Slide 13 of 43
NaI(aq)
AgI(s)
Na+(aq) NO3-(aq)
Na+ and NO3- are not reactants of precipıtation rex
General Chemistry: Chapter 5
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Net Ionic Equations
“whole formula form”:
AgNO3(aq) +NaI(aq) → AgI(s) + NaNO3(aq)
Spectator ions
ionic form:
Ag+(aq) + NO3-(aq) + Na+(aq) + I-(aq) → AgI(s) +
+ Na
Na+(aq) + NO3-(aq)
Net ionic equation:
Ag+(aq) + I-(aq) → AgI(s)
That includes only the actual participants in the rex. A net ionic eq.
must be balanced.
Slide 14 of 43
General Chemistry: Chapter 5
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Predicting Precipitation Rex
AgNO3 (aq)+ KBr(aq)
?
Write ions, see the possibilties.
Two possibilitites: 1) a precipitate occurs or 2) no rex
To predict use the table below (without doing experiment)
Slide 15 of 43
General Chemistry: Chapter 5
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5 - 16
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5-3 Acid-Base Reactions
Latin acidus
Sour taste
Arabic al-qali
Bitter taste
Acid-Base theory
Svante Arrhenius 1884
Brønsted and Lowry 1923
Figure 5-9
An acid, a base, and an acid–base indicator
Slide 17 of 43
General Chemistry: Chapter 5
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Acids
Arrhenius acids provide H+ in aqueous solution.
Strong acids completely ionize:
HCl(aq)
→
H+(aq) + Cl-(aq)
Weak acid ionization is not complete:
CH3CO2H(aq)
←
→
H+(aq) + CH3CO2-(aq)
Brønsted Lowry acids are proton donors.
H+ is transffered from one to another
HCl(aq) + H2O
Slide 18 of 43
H3O+ + ClGeneral Chemistry: Chapter 5
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Bases
Arrhenius says Bases provide OH- in aqueous solution.
Strong bases:
NaOH(aq)
→ Na+(aq) + OH-(aq)
H2O
Weak bases:
NH3(aq) + H2O(l)
←
→
OH-(aq) + NH4+(aq)
Brønsted Lowry bases are proton acceptors. Water behaves as
proton donor (B-L acid)
Most basic substances
are weak bases.
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General Chemistry: Chapter 5
Slide 20 of 43
General Chemistry: Chapter 5
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Acidic and Basic Solution
Pure water is partially ionized.
In pure water [H+]water= [OH-]water= 1x 10-7 M
An acidic sol has grater [H+] than [H+] of
water
Basic sol has greater [OH-] than [OH-] of
water
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Neutralization:
HCl(aq) + NaOH(aq)
Acid and base react with each other to form water and
soluble ionic compound, salt
Switching to the ionic forms;
HCl + NaOH
Eliminate spectators, the net neutralization rex:
H+(aq) + -OH(aq)
Slide 22 of 43
H2O(l)
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The net netralization involved with weak base:
NH3(aq) + HCl(aq)
The net ionic eq;
H+ (aq)
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+ NH3 (aq)
General Chemistry: Chapter 5
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Recognizing Acids and Bases
Acids have ionizable hydrogen atoms.
CH3CO2H or HC2H3O2
What about methane?
Bases are often indicated by combination of hydroxide ion
with various metal cations.
KOH
(CH3CH2OH- ethanol ?)
or can be identified by chemical equations
Na2CO3(s) + H2O(l)→ HCO3-(aq) + 2 Na+(aq) + OH-(aq)
Slide 24 of 43
General Chemistry: Chapter 5
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More Acid-Base Reactions
Milk of magnesia
Mg(OH)2
insoluble in water
Mg(OH)2(s) + 2 H+(aq) → Mg2+(aq) + 2 H2O(l)
Also rex with weak acids:
Mg(OH)2(s) + 2 CH3CO2H(aq) →
Mg2+(aq) + 2 CH3CO2-(aq) + 2 H2O(l)
Slide 25 of 43
General Chemistry: Chapter 5
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More Acid-Base Reactions
Limestone and marble.
CaCO3(s) + 2 H+(aq) → Ca2+(aq) + H2CO3(aq)
But: H2CO3(aq) → H2O(l) + CO2(g)
Very unstable
CaCO3(s) + 2 H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
Erosion of marble status
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General Chemistry: Chapter 5
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Erosion of marble status
Figure 5-10
Damage caused by acid rain
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General Chemistry: Chapter 5
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General Chemistry: Chapter 5
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5 - 29
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5-4
Oxidation-Reduction Reactions:
Some General Principles
Hematite is converted to iron in a blast furnace.
D
Fe2O3(s) + 3 CO(g) → 22 Fe(l)
Fe(l) +
+ 33 CO
CO2(g)
Oxidation and reduction always occur together.
Fe3+ is reduced to metallic iron.
CO(g) is oxidized to carbon dioxide.
Slide 30 of 43
General Chemistry: Chapter 5
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Fe2O3(s) + 2 Al(s)  Al2O3(s) + 2 Fe(l)
Figure 5-11
Thermite Reaction
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General Chemistry: Chapter 5
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5 - 32
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Oxidation State Changes
Assign oxidation states:
3+ 2-
2+ 2-
D
0
4+ 2-
Fe2O3(s) + 3 CO(g) → 2 Fe(l) + 3 CO2(g)
Fe3+ is reduced to metallic iron.
CO(g) is oxidized to carbon dioxide.
Slide 33 of 43
General Chemistry: Chapter 5
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Oxidation and Reduction Half-Reactions
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Figure 5-12
An oxidation-reduction reaction
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General Chemistry: Chapter 5
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The reaction represented by two half-reactions.
Oxidation:
Zn(s) → Zn2+(aq) + 2 e-
Reduction:
Cu2+(aq) + 2 e- → Cu(s)
Overall:
Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq)
Slide 35 of 43
General Chemistry: Chapter 5
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Oxidation and Reduction
Oxidation
O.S. of some element increases in the reaction.
Electrons are on the right of the equation
Reduction
O.S. of some element decreases in the reaction.
Electrons are on the left of the equation.
Slide 36 of 43
General Chemistry: Chapter 5
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5 - 37
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5 - 38
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5-5
Balancing Oxidation-Reduction
Equations
In balancing chem eq for redox rex
1. The number of atoms of each type
2. The number of electrons transffered
3. Total charges on reactants and products
Slide 39 of 43
General Chemistry: Chapter 5
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The Half-Equation Method
• Write and balance separate half-equations
for oxidation and reduction.
• Adjust coefficients in the two half-equations
so that the same number of electrons appear
in each half-equation.
• Add together the two half-equations
(canceling out electrons) to obtain the
balanced overall equation
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General Chemistry: Chapter 5
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General Chemistry: Chapter 5
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5 - 42
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General Chemistry: Chapter 5
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5 - 45
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Disproportionation Reactions
The same substance is both
oxidized and reduced.
Some have practical significance
Hydrogen peroxide
2 H2O2(aq)  H2O(l) + O2(g)
Sodium thiosulphate
2 S2O3(aq) + H+(aq)  S(s) + SO2(g) + H2O(l)
Slide 46 of 43
General Chemistry: Chapter 5
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Figure 5-14
Antiseptic action of hydrogen peroxide solution
Slide 47 of 43
General Chemistry: Chapter 5
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5-6 Oxidizing and Reducing Agents.
An oxidizing agent (oxidant)
• causes another substance to be oxidized
• contains an element whose oxidation state
decreases in a redox reaction
• gains electrons (electrons are found on the left
side of its half-equation)
• is reduced
Slide 48 of 43
General Chemistry: Chapter 5
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5-6 Oxidizing and Reducing Agents.
A reducing agent (reductant)
• causes another substance to be reduced
• contains an element whose oxidation state
increases in a redox reaction
• loses electrons (electrons are found on the right
side of its half-equation)
• is oxidized
Slide 49 of 43
General Chemistry: Chapter 5
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Figure 5-15
Oxidation states of nitrogen: Identifying oxidizing and reducing agents
Slide 50 of 43
General Chemistry: Chapter 5
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1
Oxidizing agent
2
3
Phenol
Reducing agent
Hydrazine Oxidizing agent
ozone oxidizing agent
Thiosulfate reducing agent
Slide 51 of 43
General Chemistry: Chapter 5
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Figure 5-16
Bleaching action of NaOCl(aq) is important oxidizing agent
Slide 52 of 43
General Chemistry: Chapter 5
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5 - 53
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5-7 Stoichiometry of Reactions in Aqueous
Solutions: Titrations.
Titration
Carefully controlled addition of one solution to
another.
Equivalence Point
Both reactants have reacted completely.
Indicators
Substances which change colour near an
equivalence point.
Slide 54 of 43
General Chemistry: Chapter 5
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5.0 mL CH3CO2H
A few drops
phenolpthalein
Add 0.1000 M NaOH
The “endpoint”
(close to the equivalence point)
FIGURE 5-17
An acid–base titration—Example 5-9 illustrated
Slide 55 of 43
General Chemistry: Chapter 5
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General Chemistry: Chapter 5
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5 - 57
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5 - 58
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General Chemistry
Principles & Modern Applications
10th Edition
Petrucci/Herring/Madura/Bissonnette
Chapter 5
Introduction to Reactions in Aqueous
Solutions
Dr. Wendy Pell
University of Ottawa
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Slide 59 of 25
Which of the following two solutions, when mixed,
likely result in a precipitate?
1. NaCl(aq) + MgCl2(aq)
2. NH4Cl(aq) + NaBr(aq)
3. AgNO3(aq) + NaNO3(aq)
4. MgCl2(aq) + NaOH(aq)
5. Pb(NO3)2(aq) + AgOOCCH3(aq)
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Slide 60 of 25
Which of the following two solutions, when mixed,
likely result in a precipitate?
1. NaCl(aq) + MgCl2(aq)
2. NH4Cl(aq) + NaBr(aq)
3. AgNO3(aq) + NaNO3(aq)
4. MgCl2(aq) + NaOH(aq)
5. Pb(NO3)2(aq) + AgOOCCH3(aq)
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Slide 61 of 25
Which of the following two compounds, when mixed
together, do not form a precipitate?
1. NaBr(aq) + AgNO3(aq)
2. K2SO4(aq) + BaCl2(aq)
3. Mg(ClO4)2(aq) + NaOH(aq)
4. Na3PO4(aq) + NH4Cl(aq)
5. Pb(NO3)2(aq) + NaI(aq)
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Slide 62 of 25
Which of the following two compounds, when mixed
together, do not form a precipitate?
1. NaBr(aq) + AgNO3(aq)
2. K2SO4(aq) + BaCl2(aq)
3. Mg(ClO4)2(aq) + NaOH(aq)
4. Na3PO4(aq) + NH4Cl(aq)
5. Pb(NO3)2(aq) + NaI(aq)
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Slide 63 of 25
You have three beakers each containing 200 ml of water. To the first you add
0.2 moles of solid LiCl, to the second you add of 0.4 moles AgNO3 and to the
third you add of solid 0.1 moles MgSO4. Which species will you find when you
mix the three beakers ?
a)
Li+, Cl-, Ag +, NO32-, Mg2+, SO42
b)
AgCl, Ag2SO4
c)
Li+, NO32-, Mg2+, AgCl, Ag2SO4
d)
Li+, Cl-, Ag +, NO32-, Mg2+, SO42, AgCl, Ag2SO4
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Slide 64 of 25
You have three beakers each containing 200 ml of water. To the first you add
0.2 moles of solid LiCl, to the second you add of 0.4 moles AgNO3 and to the
third you add of solid 0.1 moles MgSO4. Which species will you find when you
mix the three beakers ?
a)
Li+, Cl-, Ag +, NO32-, Mg2+, SO42
b)
AgCl, Ag2SO4
c)
Li+, NO32-, Mg2+, AgCl, Ag2SO4
d)
Li+, Cl-, Ag +, NO32-, Mg2+, SO42, AgCl, Ag2SO4
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Slide 65 of 25
The net ionic equation for the reaction that occurs when a
solution of sodium iodide (NaI) is dripped into a solution of
lead nitrate (Pb(NO3)2).
1. Na + (aq) + I  (aq) + Pb2+ (aq) + 2NO3 (aq)  NaI(s) + Pb(NO3 )2 (s)
2. NaI(aq) + Pb(NO3 )2 (aq)  NaNO3 (s) + PbI2 (s)
3. 2Na + (aq) + 2I  (aq) + Pb2+ (aq) + 2NO3 (aq)  2NaNO3 (s) + PbI 2 (s)
4. Na + (aq) + NO3 (aq)  NaNO3 (s)
5. Pb2+ (aq) + 2I  (aq)  PbI 2 (s)
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Slide 66 of 25
The net ionic equation for the reaction that occurs when a
solution of sodium iodide (NaI) is dripped into a solution of
lead nitrate (Pb(NO3)2).
1. Na + (aq) + I  (aq) + Pb2+ (aq) + 2NO3 (aq)  NaI(s) + Pb(NO3 )2 (s)
2. NaI(aq) + Pb(NO3 )2 (aq)  NaNO3 (s) + PbI2 (s)
3. 2Na + (aq) + 2I  (aq) + Pb2+ (aq) + 2NO3 (aq)  2NaNO3 (s) + PbI 2 (s)
4. Na + (aq) + NO3 (aq)  NaNO3 (s)
5 . P b 2+ (a q ) + 2 I  (a q ) 
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P b I 2 (s)
Slide 67 of 25
While changing the battery in a car, a
mechanic spills ~100 mL of sulfuric acid
(H2SO4) on the floor. The sulfuric acid in
a car battery is approximately 6 M.
Baking soda or sodium bicarbonate
(NaHCO3) can be used to neutralize the
acid spill. If the mechanic has a 3 M
solution of baking soda, what volume is
required to neutralize the acid? (Do not
use a calculator)
1. 100 mL
2. 200 mL
4. 400 mL
5. 500 mL
3. 300 mL
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Slide 68 of 25
While changing the battery in a car, a
mechanic spills ~100 mL of sulfuric acid
(H2SO4) on the floor. The sulfuric acid in
a car battery is approximately 6 M.
Baking soda or sodium bicarbonate
(NaHCO3) can be used to neutralize the
acid spill. If the mechanic has a 3 M
solution of baking soda, what volume is
required to neutralize the acid? (Do not
use a calculator)
1. 100 mL
2. 200 mL
4. 400 mL
5. 500 mL
3. 300 mL
2 NaHCO3 + H2So4
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Na2So4(aq) + 2 H2O + 2 CO2
Slide 69 of 25
In the pictures to the right, what are the probable
contents in each of the beakers?
A
1. A) H2O(l), B) NH3(aq), C) NaOH(aq)
2. A) HCl(aq), B) H2O(l), C) CH3COOH(aq)
3. A) HCl(aq), B) NH3(aq), C) H2O(l)
B
4. A) NaOH(aq), B) HCl(aq), C) H2O(l)
5. A) NH3(aq), B) CH3COOH(aq), C) HNO3(aq)
C
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Slide 70 of 25
In the pictures to the right, what are the probable
contents in each of the beakers?
A
1. A) H2O(l), B) NH3(aq), C) NaOH(aq)
2. A) HCl(aq), B) H2O(l), C) CH3COOH(aq)
3. A) HCl(aq), B) NH3(aq), C) H2O(l)
B
4. A) NaOH(aq), B) HCl(aq), C) H2O(l)
5. A) NH3(aq), B) CH3COOH(aq), C) HNO3(aq)
C
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Slide 71 of 25
The contents of the first beaker to the right is
water which is a non-electrolyte. As you are
aware the net ionic equation for the reaction
of a strong base such as NaOH and a strong
acid such as HCl is
H + (aq) + OH  (aq)  H 2O(l)
True or false, the contents of the second
beaker to the right could be 300 ml each of
2.0 M NaOH and 2.0 M HCl?
1. True
NaOH(aq)
+
HCl?
H2O
2. False
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Slide 72 of 25
The contents of the first beaker to the right is
water which is a non-electrolyte. As you are
aware the net ionic equation for the reaction
of a strong base such as NaOH and a strong
acid such as HCl is
H + (aq) + OH  (aq)  H 2O(l)
True or false, the contents of the second
beaker to the right could be 300 ml each of
2.0 M NaOH and 2.0 M HCl?
1. True
NaOH(aq)
+
HCl?
H2O
2. False
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Slide 73 of 25
Which of the following statements best explains the
observations to the right?
KMnO4
1. The NaNO2 solution dissolves KMnO4 better, leaving
no color.
2. The NO3- in the first solution oxidizes the MnO4leaving a purple color.
3. The MnO4- oxidizes the NO2- in the second solution
leaving no purple color.
4. The MnO4- reduces the NO2- in the second solution
leaving no purple color.
NaNO3
NaNO2
5. The NO3- in the first solution reduces the MnO4- leaving a purple color.
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Slide 74 of 25
Which of the following statements best explains the
observations to the right?
KMnO4
1. The NaNO2 solution dissolves KMnO4 better, leaving
no color.
2. The NO3- in the first solution oxidizes the MnO4leaving a purple color.
3. The MnO4- oxidizes the NO2- in the second solution
leaving no purple color.
4. The MnO4- reduces the NO2- in the second solution
leaving no purple color.
NaNO3
NaNO2
5. The NO3- in the first solution reduces the MnO4- leaving a purple color.
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Slide 75 of 25
Which of the statements below is true about the
following redox reaction occurring in aqueous
solution.
KMnO4(aq)
5Fe2+ + MnO4 + 8H+  5Fe3+ + Mn2+ + 4H2O
1. MnO4- is being oxidized to Mn2+
2. Mn in MnO4- undergoes a change in
oxidation state from -1 to +2.
3. O in MnO4- undergoes a change in
oxidation state from -1 to -2.
Fe2+(aq)
4. H does not change its oxidation state.
5. Fe does not change its oxidation state.
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Slide 76 of 25
Which of the statements below is true about the
following redox reaction occurring in aqueous
solution.
KMnO4(aq)
5Fe2+ + MnO4 + 8H+  5Fe3+ + Mn2+ + 4H2O
1. MnO4- is being oxidized to Mn2+
2. Mn in MnO4- undergoes a change in
oxidation state from -1 to +2.
3. O in MnO4- undergoes a change in
oxidation state from -1 to -2.
Fe2+(aq)
4. H does not change its oxidation state.
5. Fe does not change its oxidation state.
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Slide 77 of 25
Which of the following statements is false about
the thermite reaction?
2Al(s) + Fe2O3 (s)  2Fe(l) + Al2O3 (s)
1. The chemical equation given above is balanced.
2. The oxidation state of Fe in Fe2O3 is +3.
3. The oxidation state of Al in Al2O3 is +2.
4. Fe in Fe2O3 is reduced to elemental iron.
5. The oxidation state of O remains unchanged.
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Slide 78 of 25
Which of the following statements is false about
the thermite reaction?
2Al(s) + Fe2O3 (s)  2Fe(l) + Al2O3 (s)
1. The chemical equation given above is balanced.
2. The oxidation state of Fe in Fe2O3 is +3.
3. The oxidation state of Al in Al2O3 is +2.
4. Fe in Fe2O3 is reduced to elemental iron.
5. The oxidation state of O remains unchanged.
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Slide 79 of 25
In the presence of acid nitrate ion (NO3-) oxidizes
solid copper to Cu2+. The by-product is gaseous
NO2(brown). The balanced half reaction for NO3reacting to form NO2 is
1. NO3 (aq)  NO2 (g) + H 2O + e
2. NO3 (aq)  NO2 (g) + e
3. NO3 (aq) + 2H + + e  NO2 (g) + H 2O
4 . N O 3 ( a q ) + H 2 O 
2 N O 2 (g ) + 2 H
+
+ e
5. 2NO3 (aq) + 4H+ + e  2NO2 (g) + 2H2O
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Slide 80 of 25
In the presence of acid nitrate ion (NO3-) oxidizes
solid copper to Cu2+. The by-product is gaseous
NO2(brown). The balanced half reaction for NO3reacting to form NO2 is
1. NO3 (aq)  NO2 (g) + H 2O + e
2. NO3 (aq)  NO2 (g) + e
3 . N O 3 ( a q ) + 2 H
+
+ e 
N O 2 ( g ) + H 2O
4. NO3 (aq) + H 2O  2NO2 (g) + 2H + + e
5. 2NO3 (aq) + 4H+ + e  2NO2 (g) + 2H2O
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Pearson Canada Inc.
Slide 81 of 25
50 mL of solution containing Cl- is
titrated to the endpoint with 10 mL
of 0.050 M AgNO3. What was the
concentration of Cl- in the sample?
Catch: Figure 4-1 on p. 112
1. 1.0x10-3 M
2. 5.0x10-3 M
3. 1.0x10-2 M
4. 5.0x10-2 M
5. 1.0x10-1 M
Copyright © 2011
Pearson Canada Inc.
Slide 82 of 25
50 mL of solution containing Cl- is
titrated to the endpoint with 10 mL
of 0.050 M AgNO3. What was the
concentration of Cl- in the sample?
Catch: Figure 4-1 on p. 112
1. 1.0x10-3 M
2. 5.0x10-3 M
3. 1.0x10-2 M
4. 5.0x10-2 M
5. 1.0x10-1 M
Copyright © 2011
Pearson Canada Inc.
Slide 83 of 25