1. Models of Acids and Bases
Arrhenius Concept: Acids produce H+ in solution, bases produce OH ion.
Brønsted-Lowry: Acids are H+ donors, bases are proton acceptors.
HCl + H2O  Cl + H3O+
acid base
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2. Conjugate Acid/Base Pairs
HA(aq) + H2O(l)  H3O+(aq) + A(aq)
conj conj conj conj
acid base acid base 1
conjugate base: everything that remains of the acid molecule after a proton is lost.
conjugate acid: formed when the proton is transferred to the base.
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3. Acid Dissociation Constant (Ka)
HA(aq) + H2O(l)  H3O+(aq) + A(aq)
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Acid Strength
Strong Acid:
Its equilibrium position lies far to the right. (HNO3)
Yields a weak conjugate base. (NO3)
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5. Acid Strength (continued)
Weak Acid:
Its equilibrium lies far to the left. (CH3COOH)
Yields a much stronger (it is relatively strong) conjugate base than water. (CH3COO)
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6. Water as an Acid and a Base
Water is amphoteric (it can behave either as an acid or a base).
H2O + H2O  H3O+ + OH
conj conj
acid 1 base acid base 1
Kw = 1  1014 at 25°C
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The pH Scale
pH  log[H+]
pH in water ranges from 0 to 14.
Kw = 1.00  1014 = [H+] [OH]
pKw = = pH + pOH
As pH rises, pOH falls (sum = 14.00).
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8. Solving Weak Acid Equilibrium Problems
List major species in solution.
Choose species that can produce H+ and write reactions.
Based on K values, decide on dominant equilibrium.
Write equilibrium expression for dominant equilibrium.
List initial concentrations in dominant equilibrium.
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9. Solving Weak Acid Equilibrium Problems (continued)
Define change at equilibrium (as “x”).
Write equilibrium concentrations in terms of x.
Substitute equilibrium concentrations into equilibrium expression.
Solve for x the “easy way.”
Verify assumptions using 5% rule.
Calculate [H+] and pH.
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10. Percent Dissociation (Ionization)
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11. Bases
“Strong” and “weak” are used in the same sense for bases as for acids.
strong = complete dissociation (hydroxide ion supplied to solution)
NaOH(s)  Na+(aq) + OH(aq)
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12. Bases (continued)
weak = very little dissociation (or reaction with water)
H3CNH2(aq) + H2O(l)  H3CNH3+(aq) + OH(aq)
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Polyprotic Acids
. . . can furnish more than one proton (H+) to the solution.
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14. Acid-Base Properties of Salts
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15. Structure and Acid-Base Properties
Two factors for acidity in binary compounds:
Bond Polarity (high is good)
Bond Strength (low is good)
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Oxides
Acidic Oxides (Acid Anhydrides):
OX bond is strong and covalent.
SO2, NO2, CrO3
Basic Oxides (Basic Anhydrides):
OX bond is ionic.
K2O, CaO
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Lewis Acids and Bases
Lewis Acid: electron pair acceptor
Lewis Base: electron pair donor
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