Acid-Base Equilibria

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• Acid-Base Equilibria
• pH and pOH
• Relationship of Conjugate Pair acid-base
  strength.
• When acids or bases control pH
• determine K
• predict pH
• When pH controls acid/base state
• predict acid/base state
• use acid/base state to determine pH
• Buffer action
• pH titration curves

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pH/pOH Calculations
H3OOH- 1.0 x 10-14 pH -logH3O
pOH -logOH- H3O 10-pH OH-
10-pH pH pOH 14.00
What is the pH of a solution with H3O 4.6 x
10-5 What is the pOH of a solution with
OH- 3.3 x 10-4 What is the pOH of a
solution with H3O 2.4 x 10-3 What is
H3O when pH 4.2
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Strong acids and bases
For strong acid solutions, H3O acid
(except for H2SO4) For strong bases LiOH,
NaOH, KOH, RbOH, OH- base For strong bases
Ca(OH)2, Ba(OH)2, etc., OH- 2 x base
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What is the pH when H3O 0.045 M?

1. 0.045
2. 13.995
3. -1.35
4. 1.35

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What is the pH when OH- 6.5 x 10-4 M?

1. 3.18
2. -3.18
3. 10.81
4. 15.18

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What is the H3O when pH 3.66 M?

1. 2.18 x 10-4
2. 10.34
3. 4570
4. 3.66

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What is the OH- when pH 5.84 M?

1. 1.45 x 108
2. 3.31 x 10-6
3. 6.92 x 10-9
4. 5.84

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Acid-Base Equilibria Bronsted Acid H (proton)
donor Bronsted Base H acceptor Acid-Base
reactions H transfer reaction Conjugate
Acid-Base Pairs acid
conjugate base HF F- NH4 NH3
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What is the conjugage base of HNO2?

1. H2NO2
2. HNO3
3. NO2-

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What is the conjugage acid of HPO42-?

1. H2PO4-
2. H3PO4
3. PO43-

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Acid-Base Strength Depends on Equilibrium
Constant
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Trends in relative acid/base strength for
conjugate pairs.
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Determining the Ka Value What is the value of Ka
for an acid, HA, for which a 0.240 M solution
has a pH of 3.28?
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Determining Kb A 0.300 M solution of a weak
base has a pH of 9.20. What is Kb?
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What is the pH of a 0.150 M solution of HCl?
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What is the pH of a 0.150 M solution of HF?
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What is the pH of a 0.150 M solution of HCN?
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What is the pH of a 0.150 M solution of Ca(OH)2?
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What is the pH of a 0.150 M solution of NH3?
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Polyprotic Acids
H2CO3 HCO3- CO32-
H3PO4 H2PO4 -
HPO4 2- PO4 3-
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