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1
Please Pick Up

• Blank IDIRICE grids
• Small lettered titration volume sheet

2
Aqueous Neutralization Reactions

• Edward A. Mottel
• Department of Chemistry
• Rose-Hulman Institute of Technology

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Aqueous Neutralization Reactions

• Reading assignment
• Chang Chapter 16.2-16.4

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Potentiometric Titration 20.0 mL of 0.400 M HCl
with Aqueous Ammonia
Why does the pH change rapidly at the equivalence
point?
5
So maybe you would like to be a CPA?
(Chemistry Problem Analyzer)
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Hydrofluoric Acid Solution

• What is the pH of a 20.0 mL of 0.100 M
  hydrofluoric acid at 25 C?

H
HF
HF
HF
F-
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Substitute into theMass-Action Expression
0.100
x
x
0.100-x
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Solve for H
x 0.00813, -0.00885
pH - log H - log (0.00813)
pH 2.09
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Percentage Ionization
x 0.00813
What percentage of this solution is ionized?
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IDIRICE

• Initial 1
• Dissociation
• Initial 2
• Reaction
• Initial 3
• M
• Change
• Equilibrium

• Convert to moles
• Strong electrolytes dissociate 100
• Sum of previous two steps
• Favorable (Kgt1) reactions occur 100
• Sum of previous two steps
• Convert to concentration
• Most favorable unfavorable reaction
• Use in mass-action expression

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Hydrofluoric Acid Solution

• 20.0 mL of 0.100 M hydrofluoric acid
• Write the dissociation reaction including proper
  equilibrium arrow notation.
• What species (molecules and ions) might be
  important in determining the pH of this solution?

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Initial Line 1 (I line) Millimoles
How many millimoles of HF are initially present?
20.0 mL x 0.100 M
2.00 mmoles
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lots
2.00
0
0
0
Start with the initial conditions
Is HF a strong acid?
Does HF dissociate 100?
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R LineCross-Reactions

• There are two chemical species present in
  solution HF H2O
• What acid-base cross reactions are possible?
• HF HF
• HF H2O
• H2O H2O
• How could you tell if any of these reactions are
  favorable?

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Consider Reactions of Molecules and Ions Which
Are Present
Are any of these reactions favorable?
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lots
0.100
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C LineIdentify the Most Favorable Unfavorable
Reaction
This is the equilibrium reaction.
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-x
x
x
-x
Let -x equal the amount of HF which reacts.
H and H3O are the same ion
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Substitute into theMass-Action Expression
21
Solve for H
x 0.00813, -0.00885
pH - log H - log (0.00813)
pH 2.09
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pH Before the Equivalence Point
What is the pH of a solution containing 20.0 mL
of 0.100 M hydrofluoric acid and 10.0 mL of 0.100
M potassium hydroxide at 25 C?
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IDIRICE

• Initial 1
• Dissociation
• Initial 2
• Reaction
• Initial 3
• M
• Change
• Equilibrium

• Convert to moles
• Strong electrolytes dissociate 100
• Sum of previous two steps
• Favorable (Kgt1) reactions occur 100
• Sum of previous two steps
• Convert to concentration
• Most favorable unfavorable reaction
• Use in mass-action expression

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Did you hear about the new pirate movie?
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pH Before the Equivalence Point

• 20.0 mL of 0.100 M HF
• 10.0 mL of 0.100 M KOH

How many millimoles of each reactant are there?
20.0 mL x 0.100 M
2.00 mmoles of HF
10.0 mL x 0.100 M
1.00 mmoles of KOH
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lots
0
0
-1.00
1.00
1.00
lots
0
1.00
1.00
Start with the initial conditions
Is HF a strong acid? Does HF dissociate 100?
Is KOH a strong base? Does KOH dissociate 100?
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Consider the Cross Reactions
What chemical species are available to react?
HF, K, OH, H2O
Are the cross-reactions of any of these
species favorable (Kgt1)?
Hint acid-base reactions are usually
favorable identify any acids and bases
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Cross-ReactionsWhich of these reactions are
favorable?

• HF HF
• HF K
• HF OH-
• HF H2O
• K K
• K OH-
• K H2O

• OH- OH-
• OH- H2O
• H2O H2O

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Cross-ReactionsWhich of these reactions are
favorable?
K 1
K gt 1
K lt 1
HF HF
HF OH-
OH- H2O
HF K
HF H2O
K K
K OH-
K H2O
OH- OH-
H2O H2O
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-1.00
-1.00
1.00
1.00
1.00
1.00
1.00
0.00
lots1
What is the limiting reagent?
How many millimoles of hydroxide ion react?
How many millimoles of HF react?
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lots
0.033
0.033
0.033
Assume volumes are additive. What is the total
volume of solution?
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Cross-ReactionsWhich of these reactions are
favorable?

• HF HF
• HF F-
• HF K
• HF H2O
• F- F-
• F- K
• F- H2O

• K K
• K H2O
• H2O H2O

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Equilibrium ReactionWhich of these reactions are
favorable?
K 1
K gt 1
K lt 1
HF HF
HF F-
HF K
HF H2O
F- F-
F- K
F- H2O
K K
K H2O
H2O H2O
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Why is this anEquilibrium Reaction?
What was the goal of the calculation?
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-x
x
x
-x
x
0.033-x
0.033x
0.033
lots-x
Let -x equal the amount of HF which reacts.
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Solve for H
x 0.033x
7.2 x 104
0.033 - x
x 6.9 x 104, -0.0344
pH - log H - log (6.9 x 10-4)
pH 3.16
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Work out the pH of the solution for your second
data point
return to IDIRICE
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pH After the Equivalence Point

• 20.0 mL of 0.100 M HF
• 30.0 mL of 0.100 M KOH

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lots
0
0
-3.00
3.00
3.00
lots
0
3.00
3.00
Start with the initial conditions
Is HF a strong acid? Does HF dissociate 100?
Is KOH a strong base? Does KOH dissociate 100?
43
Cross-ReactionsWhich of these reactions are
favorable?

• HF HF
• HF K
• HF OH-
• HF H2O
• K K
• K OH-
• K H2O

• OH- OH-
• OH- H2O
• H2O H2O

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Cross-ReactionsWhich of these reactions are
favorable?
K 1
K gt 1
K lt 1
HF HF
HF OH-
OH- H2O
HF K
HF H2O
K K
K OH-
K H2O
OH- OH-
H2O H2O
What is the best available base?
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-2.00
-2.00
2.00
2.00
0
2.00
3.00
1.00
lots2
What is the limiting reagent?
How many millimoles of HF reactant?
How many millimoles of hydroxide ion reactant?
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20.0 mL of 0.100 M HF is titrated with 30.0 mL of
0.100 M KOH
lots
0.040
0.060
0.020
Assume volumes are additive. What is the total
volume of solution?
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Cross-ReactionsWhich of these reactions are
favorable?

• F- F-
• F- K
• F- OH-
• F- H2O
• K K
• K OH-
• K H2O

• OH- OH-
• OH- H2O
• H2O H2O

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Equilibrium ReactionWhich of these reactions are
favorable?
K 1
K gt 1
K lt 1
OH- H2O
F- F-
F- K
F- OH-
F- H2O
K K
K OH-
K H2O
What is the best available base?
OH- OH-
H2O H2O
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Why is this anEquilibrium Reaction?
What was the goal of the calculation?
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x
x
-x
x
0.060
0.020x
lots-x
0.040
Let x equal the amount of H which forms.
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Solve for H
H OH Kw
x 0.020x 1.0 x 1014
x 5.0 x 1013, -0.020
pH - log H - log (5.0 x 10-13)
pH 12.30
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Titration of 20.0 mL of 0.100 M HF with 0.100 M
KOH
Vol KOH
pH
0.0
2.09
4.0
2.62
8.0
2.98
10.0
3.16
12.0
3.33
16.0
3.75
18.0
4.10
19.5
4.74
?
20.0
11.08
20.5
11.68
22.0
11.95
24.0
12.23
28.0
12.30
30.0
12.36
32.0
12.46
36.0
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Weak Acid - Strong Base Problem Set
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Hydrolysis Reactions

• Reading assignment
• Chang Chapter 15.10

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pH at the Equivalence Point
20.0 mL of 0.100 M HF
?? mL of 0.100 M KOH
20.0 mL of 0.100 M KOH
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lots
0
0
-2.00
2.00
2.00
lots
0
2.00
2.00
Start with the initial conditions
Is HF a strong acid? Does HF dissociate 100?
Is KOH a strong base? Does KOH dissociate 100?
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Cross-ReactionsWhich of these reactions are
favorable?

• HF HF
• HF K
• HF OH-
• HF H2O
• K K
• K OH-
• K H2O

• OH- OH-
• OH- H2O
• H2O H2O

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Cross-ReactionsWhich of these reactions are
favorable?
K 1
K gt 1
K lt 1
HF HF
HF OH-
OH- H2O
HF K
HF H2O
K K
K OH-
K H2O
OH- OH-
H2O H2O
What is the best available base?
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-2.00
-2.00
2.00
2.00
0
2.00
2.00
0
lots2
What is the limiting reagent?
How many millimoles of HF reactant?
How many millimoles of hydroxide ion reactant?
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lots
0.050
0.050
Assume volumes are additive. What is the total
volume of solution?
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Cross-ReactionsWhich of these reactions are
favorable?

• F- F-
• F- K
• F- H2O
• K K
• K H2O
• H2O H2O

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Equilibrium ReactionWhich of these reactions are
favorable?
K 1
K gt 1
K lt 1
F- F-
F- K
F- H2O
K K
K H2O
H2O H2O
What is the best available base?
What is the best acid - base reaction?
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StrategyHow to get at the pH
And solve for OH
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x
x
-x
-x
x
x
0.050
lots-x
0.050-x
Let x equal the amount of OH which forms.
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What is the Equilibrium Constant for
1 / 7.2 x 104 M
1.0 x 1014 M2
1.4 x 1011 M
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Solve for OH
(x) (x)
1.4 x 1011 M

0.050 - x
x 8.3 x 107 , - 8.3 x 107
OH 8.3 x 107 M
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Solve for H then pH
H OH Kw
y 8.3 x 107 y 1.0 x 1014 M2
y 1.2 x 108 M
H 1.2 x 108 M
pH - log H - log (1.2 x 108)
pH 7.92
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Group Activity

• What species are predominately present when
• 20.0 mL of 0.100 M HF reacts with
• 20.0 mL of 0.100 M KOH?
• Give another way in which a solution containing
• 2.00 mmol of K and 2.00 mmol of F in 40.0 mL of
  solution could be prepared.

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pH of a Salt

• What is the pH of a salt solution containing
• 2.00 mmol of KF in 40.0 mL of solution?
• Why is the pH of the solution not neutral? (not
  equal to 7)

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pH of a SaltpH at the Equivalence Point
HCl NaOH
NaCl
7
HNO3 NH3
NH4NO3
below 7
above 7
H2CO3 KOH
KHCO3
near 7
HF N2H4
N2H5F
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Predict whether aqueous solutions of the
following salts should be acidic, basic or
neutral.
KBr
HBr KOH
HBr KOH
HBr KOH
neutral
Na2CO3
NaHCO3 NaOH
NaHCO3 NaOH
NaHCO3 NaOH
basic
NaHCO3
H2CO3 NaOH
H2CO3 NaOH
H2CO3 NaOH
basic
NH4I
HI NH3
HI NH3
HI NH3
acidic
CH3NH3F
HF CH3NH2
HF CH3NH2
HF CH3NH2
neutral
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Conductometric Titration
Depending on the acid-base system studied, the
graph may have many different shapes.
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Conductometric Titration
Why does the line change slope?
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Conductometric Titration
Total
K
OH
H
Cl
Ions
100
20
50
30
0
20
100
40
100
60
120
80
160
100
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Conductometric Titration
If the total number of ions isnt changing before
the equivalence point, why is the conductivity
changing?
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Laboratory Schedule forThis Week and Next Week

• A standardized KOH solution will be provided.
• Determine the molarity of the acid (HCl) using
• indicator titration with the KOH. (two different
  indicators)
• potentiometric titration
• conductometric titration
• Determine the properties of an unknown solution.
  It could be an acid, a base or a salt.
• Analyze the unknown solution using the pH,
  conductometric and indicator titration with
  either the HCl or KOH (as appropriate).

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Please Pick Up

• Two (2) pages of blank IDIRICE grids
• Sample IDIRICE filled out grid
• Small lettered titration volume sheet