Acids, Bases

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Chapter 8 9

• Acids, Bases Buffers

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Chapter 8 Introducing Acids Bases

• Water pH (Acid rain) in the USA in 2001

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Conjugate acids bases
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Relation between H, OH-, and pH?
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8-3 Strengths of acids bases

• Strong Acids and Bases
• Common strong acids and bases are listed in Table
  8-1.
• A strong acid or strong base is completely
  dissociated in aqueous solution.
• 
  
• 
  (8-4)
• 
  (8-5)

P.175
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• Carboxylic Acids Are Weak Acids and Amines Are
  Weak Bases
• 
  (8-6)

P.175
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8-3 Strengths of acids bases
Carboxylic Acids are Weak Acids and Amines are
Weak Bases

• Ask yourself at p.178

8

• Metal Ions with Charge ?2 Are Weak Acids
• A proton can dissociate from M(H2O)wn to reduce
  the positive charge on the metal complex.

Relation Between Ka and Kb
P.177
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8-4 pH of strong Acids Bases

• Example at p.180
• The pH of 4.2 x 10-3 M HClO4 ?
• The pH of 4.2 x 10-3 M KOH?
• Can we dissolve base in water and obtain an
  acidic pH (lt7)?

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8-5 Tools for Dealing with Weak Acids and Bases

• pK the negative logarithm of an equilibrium
  constant
• Weak Is Conjugate to Weak
• The conjugate base of a weak acid is a weak base.
  The conjugate acid of a weak base is a weak acid.

P.181
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• Using Appendix B
• Acid dissociation constants appear in Appendix B.
  Each compound is shown in its fully protonated
  form.
• Pyridoxal phosphate is given in its fully
  protonated form as follows

•  

P.182
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P.182
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8-6 Weak-Acid Equilibrium

P.182
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• Fraction of Dissociation
• Figure 8-4 compares the fraction of dissociation
  of two weak acids as a function of formal
  concentration.
• acid increase as it is diluted.

P.184
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Chapter 9 Buffers

• Buffered solution resists changes in pH when
  small amounts of acids or base are added or when
  dilution occurs.

• pH dependence of the rate of a particular
  enzyme-catalyzed reaction.
• The rate near pH 8 is twice as the rate at pH 7
  or 9

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9.2 The Henderson-Hasselbalch eqn
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If pH pKa, HA A-If pH lt pKa, HA gt
A-If pH gt pKa, HA lt A-
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9-3 A Buffer in Action

• Example find the pH of a buffer solution at p.
  198
• Effect of adding acid to a buffer

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9-4 Preparing Buffers

• Example at p. 202
• In the real life p. 203

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• Preparing a Buffer in Real Life
• Suppose you wish to prepare 1.00 L of buffer
  containing 0.100 M tris at pH 7.60. When we say
  0.100 M tris, we mean that the total
  concentration of tris plus tris H will be
  0.100M. 
• Procedure
• 1. Weigh out 0.100 mol tris hydrochloride and
  dissolve it in a beaker containing about 800 mL
  water and a stirring bar. 
• 2. Place a pH electrode in the solution and
  monitor the pH.
• 3. Add NaOH solution until the pH is exactly
  7.60. The electrode does not respond instantly.
• 4. Transfer the solution to a volumetric flask
  and wash the beaker and stirring bar a few times.
  Add the washings to the volumetric flask. 
• 5. Dilute to the mark and mix.

P.202
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9.5 Buffer capacity -1
Buffer capacity measures how well a solution
resists changes in pH when acid or base is added.
The greater the buffer capacity, the less the pH
changes. 

• The amount of H or OH-
• that buffered solution can
• absorb without a significant
• change in pH

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9.5 Buffer capacity -2
2) Magnitudes of HA and A- ? the
capacity of a buffered soln. Ex soln A 5.00
M HOAc 5.00 M NaOAc soln B 0.05 M
HOAc 0.05 M NaOAc pH change when 0.01
mol of HCl(g) is added
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9.5 Buffer capacity -3

• 3) A- / HA ratio ? the pH of a buffered
  soln.

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• Table 9-2 Structures and pKa values for common
  buffers

P.205
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9.6 How indicators work -1

• 1) Usually a weak organic acid or base that has
  distinctly different colors in its nonionized
  ionized forms.
• HIn(aq) ? H(aq) In-(aq) pKHIn
• nonionized ionized
• form form

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9.6 How indicators work -2

• 1)
• 2)
• 3)

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9.6 How indicators work -3

• 2) The useful pH range for indicator is
• pKHIn 1
• ? (Fig
  10.3)
• encompass the pH at equivalence point
• 
  (titration curve)
• Not all indicators change color at the same pH.
  (Table 9.3)

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Table 9-3
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Two different sets of colors