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1-Step Dissociation Reaction
desaturation,
ionization |
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In the
one-step dissociation
(or ionization or desaturation)
reaction, protonated or saturated
acetic acid releases an H+
(hydronium) ion converting into deprotonated
or desaturated acetate ion. |
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The "dissociation
fraction" (Yd)
of dissociated acetic acid at
equilibrium is proportional to the equilibrium H+
concentration, [H+],
and acetic acid's dissociation
equilibrium constant (Kdn). |
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1-Step Association
Reaction
saturation, protonation |
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In the one-step association
(or protonation or saturation)
reaction, deprotonated or desaturated
acetate ion
binds an H+
(hydronium) ion converting into protonated
or saturated acetic acid. |
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The "association
fraction" or saturation
fraction (Ya)
of associated acetic acid at equilibrium is proportional to the equilibrium
H+ concentration, [H+],
and acetic acid's association equilibrium constant (Kan). |
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Chemical and
Mathematical Formulation:
Top |
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[ CH3COOH]
= [HAc] = acetic acid equilibrium
concentration |
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[ CH3COO-] = [Ac-] =
acetate equilibrium concentration |
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Co
= [Ac- ] + [ HAc ]
= the total equilibrium concentrations of acetic acid plus acetate. |
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Yd
= the "dissociated fraction," the total
fraction of all molecules in solution that are ionized or
deprotonated. |
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Ya
= the "associated "
or "saturated
fraction," the total
fraction of all molecules in solution that are protonated acetic
acid molecules. |
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Yd
+ Ya
= 1: The fractions of all molecules have to add up to
one. |
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Quantitative Relationships Derived from the Equation for the Equilibrium
Dissociation
Constant, Kdn
Top |
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Note:
pKdn
= -log(Kdn);
Kdn
= 10-pKdn
pH =
-log[H+]; & [H+] = 10-pH |
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Recommended Exercises:
Top |
| 1. |
Prove that
Kdn
= [H+]50%, where
[H+]50% = the H+
concentration at 50% saturation.
Hint: Determine [H+] at Ya = 0.5
or Yd
= 0.5
(i.e., at "50% saturation"). |
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| 2. |
Prove that
 where
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| 3. |
Prove that
Kan
= 1/[H+]50%, where
[H+]50% = H+
concentration at 50% saturation.
Hint: Determine [H+] at Ya = 0.5 or
Yd
= 0.5 (i.e., at "50% saturation"). |
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