Transcript Acids and Bases - Evangel University

Acids and Bases
Chapter 16
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Acids
Have a _________ taste. Vinegar owes its taste to
acetic acid. Citrus fruits contain citric acid.
React with certain metals to produce ______________ gas.
React with carbonates and bicarbonates to produce
______________ ______________ gas
Bases
Have a __________ taste.
Feel ________________. Many soaps contain bases.
16.3
_________ acid is a substance that produces H+ (H3O+) in water
_________ base is a substance that produces OH- in water
16.3
A __________________ acid is a proton donor
A __________________ base is a proton acceptor
base
base
acid
acid
base
acid
conjugate
acid
conjugate
base
16.1
Acid-Base Properties of Water
H+ (aq) + OH- (aq)
H2O (l)
__________________ of water
H
O
H
+ H
[H
O
H
]
H
+ H
O
-
H
base
H2O + H2O
acid
O
+
conjugate
acid
H3O+ + OHconjugate
base
16.2
The Ion Product of Water
H2O (l)
H+ (aq) + OH- (aq)
[H+][OH-]
Kc =
[H2O]
[H2O] = constant
Kc[H2O] = Kw = [H+][OH-]
The __________________(Kw) is the product of
the molar concentrations of H+ and OH- ions at a
particular _______________________.
Solution Is
[H+] = [OH-]
At 250C
Kw = [H+][OH-] = __________
[H+] > [OH-]
[H+] < [OH-]
16.2
What is the concentration of OH- ions in an HCl
solution whose hydrogen ion concentration is 1.3 M?
Kw = [H+][OH-] = _____________
[H+] = _____________M
[OH-]
Kw
=
=
+
[H ]
= _____________ M
16.2
pH – A Measure of Acidity
pH = _______________________
[H+] = [OH-]
At 250C
[H+] = 1 x 10-7
pH
acidic
[H+] > [OH-]
[H+] > 1 x 10-7
pH
basic
[H+] < [OH-]
[H+] < 1 x 10-7
pH
Solution Is
neutral
pH
[H+]
pH
[H+]
16.3
pHs of some common fluids
pOH = -log [OH-]
[H+][OH-] = Kw = _____________
-log [H+] – log [OH-] = ________
pH + pOH = _____________
16.3
The pH of rainwater collected in a certain region of the
northeastern United States on a particular day was 4.82.
What is the H+ ion concentration of the rainwater?
pH = -log [H+]
-antilog (pH) = -antilog (-log [H+])
antilog -4.82 = [H+]
[H+] = 10-pH = 10-4.82 = _____________ M
16.3
The OH- ion concentration of a blood sample is
2.5 x 10-7 M. What is the pH of the blood?
pH + pOH = _________
pOH = -log [OH-] = -log (2.5 x 10-7) = _________
pH = 14.00 – pOH = 14.00 – 6.60 = _________
16.3
Strong Electrolyte = __________________________
NaCl (s)
H 2O
Na+ (aq) + Cl- (aq)
Weak Electrolyte = __________________________
CH3COOH
CH3COO- (aq) + H+ (aq)
Strong Acids are strong electrolytes
HCl (aq) + H2O (l)
H3O+ (aq) + Cl- (aq)
HNO3 (aq) + H2O (l)
H3O+ (aq) + NO3- (aq)
HClO4 (aq) + H2O (l)
H3O+ (aq) + ClO4- (aq)
H2SO4 (aq) + H2O (l)
H3O+ (aq) + HSO4- (aq)
16.4
Weak Acids are weak electrolytes
H3O+ (aq) + F- (aq)
HF (aq) + H2O (l)
HNO2 (aq) + H2O (l)
H3O+ (aq) + NO2- (aq)
HSO4- (aq) + H2O (l)
H3O+ (aq) + SO42- (aq)
H2O (l) + H2O (l)
H3O+ (aq) + OH- (aq)
Strong Bases are strong electrolytes
NaOH (s)
KOH (s)
H 2O
H 2O
Ba(OH)2 (s)
Na+ (aq) + OH- (aq)
K+ (aq) + OH- (aq)
H 2O
Ba2+ (aq) + 2OH- (aq)
16.4
Weak Bases are weak electrolytes
F- (aq) + H2O (l)
NO2- (aq) + H2O (l)
OH- (aq) + HF (aq)
OH- (aq) + HNO2 (aq)
Conjugate acid-base pairs:
•
The conjugate base of a strong acid has no
measurable strength.
•
H3O+ is the strongest acid that can exist in
aqueous solution.
•
The OH- ion is the strongest base that can exist in
aqueous solution.
16.4
Relative Strengths of Conjugate Acid-Base Pairs
16.4
Strong Acid
Weak Acid
16.4
What is the pH of a 2 x 10-3 M HNO3 solution?
HNO3 is __________________________.
Start 0.002 M
HNO3 (aq) + H2O (l)
End
0.0 M
0.0 M
0.0 M
H3O+ (aq) + NO3- (aq)
0.002 M
0.002 M
pH = -log [H+] = -log [H3O+] = -log(0.002) = _______
16.4
What is the pH of a 1.8 x 10-2 M Ba(OH)2 solution?
Ba(OH)2 is a strong base – 100% dissociation.
Start 0.018 M
Ba(OH)2 (s)
End
0.0 M
0.0 M
0.0 M
Ba2+ (aq) + 2OH- (aq)
0.018 M
0.036 M
pH = 14.00 – pOH = 14.00 + log(0.036) = _______
16.4
Weak Acids (HA) and Acid Ionization Constants
HA (aq) + H2O (l)
H3O+ (aq) + A- (aq)
H+ (aq) + A- (aq)
HA (aq)
Ka =
Ka is the acid ionization constant
Ka
weak acid
strength
16.5
Ionization Constants of Some Weak Acids and Their Conjugate Bases at 25ºC
16.5
What is the pH of a 0.5 M HF solution (at 250C)?
+][F-]
[H
= 7.1 x 10-4
Ka =
HF (aq)
H+ (aq) + F- (aq)
[HF]
HF (aq)
Initial (M)
Change (M)
H+ (aq) + F- (aq)
0.50
0.00
0.00
-x
+x
+x
Equilibrium (M)
= __________
Ka 
= __________ x2 = __________ x = _______M
[H+] = [F-] = 0.019 M
[HF] = 0.50 – x = 0.48 M
Ka << 1
0.50 – x  0.50
Ka =
pH = -log [H+] = _________
16.5
When can I use the approximation?
Ka << 1
0.50 – x  0.50
When x is less than 5% of the value from which it is subtracted.
x = 0.019
0.019 M
x 100% = 3.8%
0.50 M
Less than 5%
Approximation ok.
What is the pH of a 0.05 M HF solution (at 250C)?
x2
Ka 
= 7.1 x 10-4 x = 0.006 M
0.05
More than 5%
0.006 M
x 100% = 12%
0.05 M
Approximation not ok.
Must solve for x exactly using quadratic equation
or method of successive approximation.
16.5
Solving weak acid ionization problems:
1. Identify the major species that can affect the pH.
•
In most cases, you can ignore the autoionization
of water.
•
Ignore [OH-] because it is determined by [H+].
2. Use ICE to express the equilibrium concentrations in
terms of single unknown x.
3. Write Ka in terms of equilibrium concentrations.
Solve for x by the approximate method. If
approximation is not valid, solve for x exactly.
4. Calculate concentration of all species and/or pH of
the solution.
16.5
What is the pH of a 0.122 M monoprotic acid
whose Ka is 5.7 x 10-4?
HA (aq)
Initial (M)
Change (M)
H+ (aq) + A- (aq)
0.122
0.00
0.00
-x
+x
+x
Equilibrium (M)
= __________
Ka 
= __________ x2 = _________
0.0083 M
x 100% = 6.8%
0.122 M
Ka << 1
0.122 – x  0.122
Ka =
x = _______ M
More than 5%
Approximation not ok.
16.5
x2
= 5.7 x 10-4
Ka =
0.122 - x
ax2 + bx + c =0
x = 0.0081
HA (aq)
Initial (M)
Change (M)
Equilibrium (M)
x2 + 0.00057x – 6.95 x 10-5 = 0
-b ± b2 – 4ac
x=
2a
x = - 0.0081
H+ (aq) + A- (aq)
0.122
0.00
0.00
-x
+x
+x
0.122 - x
x
x
[H+] = x = 0.0081 M
pH = -log[H+] = 2.09
16.5
Ionized acid concentration at equilibrium
percent ionization =
x 100%
Initial concentration of acid
For a monoprotic acid HA
Percent ionization =
[H+]
[HA]0
x 100%
[HA]0 = initial concentration
16.5
Weak Bases and Base Ionization Constants
NH3 (aq) + H2O (l)
NH4+ (aq) + OH- (aq)
[NH4+][OH-]
Kb =
[NH3]
Kb is the base ionization constant
Kb
weak base
strength
Solve weak base problems like weak acids
except solve for [OH-] instead of [H+].
16.6
Ionization Constants of Some Weak Bases and Their Conjugate Bases at 25ºC
16.6
Ionization Constants of Conjugate Acid-Base Pairs
HA (aq)
A- (aq) + H2O (l)
H2O (l)
H+ (aq) + A- (aq)
OH- (aq) + HA (aq)
H+ (aq) + OH- (aq)
Ka
Kb
Kw
KaKb = _____
Weak Acid and Its Conjugate Base
Kw
Ka =
Kb
Kw
Kb =
Ka
16.7
Ionization Constants
of Some Diprotic
Acids and a
Polyprotic Acid and
Their Conjugate
Bases at 25ºC
16.8
Molecular Structure and Acid Strength
H X
H+ + X-
The
stronger
the bond
The
weaker
the acid
Bond Energies for Hydrogen Halides and Acid Strengths for Hydrohalic Acids
HF
HCl
HBr
HI
16.9
Molecular Structure and Acid Strength
Z
dO
d+
H
Z
O- + H+
The O-H bond will be more polar and easier to break if:
•
Z is very electronegative or
•
Z is in a high oxidation state
16.9
Molecular Structure and Acid Strength
1. Oxoacids having different central atoms (Z)
that are from the same group and that have
the same oxidation number.
••
••
••
••
••
••
Acid strength increases with increasing electronegativity of Z
••
••
O
O
••
••
••
••
H O Cl O
H O Br O
•• •• • •
•• •• • •
Cl is more electronegative than Br
HClO3 > HBrO3
16.9
Molecular Structure and Acid Strength
2. Oxoacids having the same central atom (Z)
but different numbers of attached groups.
Acid strength increases as the oxidation number of Z increases.
HClO4
HClO3
HClO2
HClO
16.9
Acid-Base Properties of Salts
Neutral Solutions:
Salts containing an alkali metal or alkaline earth metal
ion (except Be2+) and the conjugate base of a strong
acid (e.g. Cl-, Br-, and NO3-).
NaCl (s)
H2O
Na+ (aq) + Cl- (aq)
Basic Solutions:
Salts derived from a strong base and a weak acid.
CH3COONa (s)
H 2O
CH3COO- (aq) + H2O (l)
Na+ (aq) + CH3COO- (aq)
CH3COOH (aq) + OH- (aq)
16.10
Acid-Base Properties of Salts
Acidic Solutions:
Salts derived from a strong acid and a weak base.
NH4Cl (s)
NH4+ (aq)
H2O
NH4+ (aq) + Cl- (aq)
NH3 (aq) + H+ (aq)
Salts with small, highly charged metal cations
(e.g. Al3+, Cr3+, and Be2+) and the conjugate
base of a strong acid.
Al(H2O)3+
6 (aq)
Al(OH)(H2O)52+(aq) + H+ (aq)
16.10
Acid Hydrolysis of Al3+
16.10
Acid-Base Properties of Salts
Solutions in which both the cation and the anion hydrolyze:
•
Kb for the anion > Ka for the cation, solution will be ________
•
Kb for the anion < Ka for the cation, solution will be ________
•
Kb for the anion  Ka for the cation, solution will be ________
Acid-Base Properties of Salts
16.10
Oxides of the Representative Elements
In Their Highest Oxidation States
16.11
Definition of An Acid
_____________ is a substance that produces H+ (H3O+) in water
A __________________ __________ is a proton donor
A __________ is a substance that can accept a pair of electrons
A __________ is a substance that can donate a pair of electrons
••
•• + OH
••
acid base
H+
H+ +
acid
••
H
N H
H
base
••
H O H
••
H
H N H
H
16.12
Lewis Acids and Bases
F B
F
+
••
H
F
N H
H
F
F B
F
H
N H
H
Which is the acid? Which is the base?
Are any protons donated or accepted?
16.12