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Unformatted text preview: a pKa, sketch the t itration
Acid OH- Acid dissociation constant
Take l og of both sides 1 What is the p Ka o f water?
pKa = pH - log( [OH- ]/[H2O] ) ; Rearranged the H-H Eq.
Values needed to solve the equation:
[Water] is ~55.5 M
pH of water is 7, so [OH-] is 1 X 10-7 M 5) Report the buffering range. pKa of water is 15.7!
What does the “pKa o f water is 15.7” really mean?
Water rarely dissociates to donate a proton. In pure water only
1 in 555,000,000 water molecules is ionized to H+ and OH(55.5 M / 1 X 10-7 M). 1 pKa predicts the leaving group. pKa tells how strongly the
acid/base wants the proton The conjugate acid with the lowest pKa
H2O vs HCl
OH- OH OH
C H H Cl- H H H H
C C H Cl H H Cl Methanol Methyl Chloride One of the many secrets of life:
Turning Bad Leaving Groups into Good Leaving Groups! CO2 Buffering
Acid What you need to know about pKa Bicarbonate Carbonate H+ H+
HCO3 CO2 + H2 O <-> H2CO3 pKa determines buffering range
(pKa ± 1 pH unit) CO3 2
H+ H+ pKa tells how strongly the
acid/base wants the proton!
pKa predicts what the leaving group will be.
(The conjugate acid with the lowest pKa) CO2...
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This note was uploaded on 04/17/2012 for the course BCMB 3100 taught by Professor Mendicino during the Spring '07 term at UGA.
- Spring '07