LEC 4-5 - ] log [A ] [HA] pK a = pH log [A ] [HA] pH = pK a...

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Biological Sciences 102                         Prof R Holland Cheng     http://pioms.ucdavis.edu/     Classes of acid/base problems   Four Classes of acid/base problems    Class 1: "Acid” form only     Class 2: "Base” form only    Class 3: "Acid" plus "Base" forms    Class 4: Polyprotic acids - amphoteric substances     Short list of equations discussed     HA   H +  + A -   —   K a = [H + ][A ] [HA]    A -  + H 2  HA + OH -   —  K b  =  [HA][OH - ] [A - ]      K w  = K eq  [H 2 O] = [H + ][OH - ] = 10 -14      pK b  = 14 – pK a   K a = [H + ][A ] [HA] logK a = log [H + ][A ] [HA] logK a = log[H + ]+log [A ] [HA] logK a =− log[H +
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Unformatted text preview: ] log [A ] [HA] pK a = pH log [A ] [HA] pH = pK a + log [A ] [HA] A simplified way is to consider when one molecule of HA- dissociates to give an H + , another molecule of HA- can pick it up to give H 2 A: HA- H + + A 2- K eq = K a2 H + + HA- H 2 A K eq = 1/K a1 Net reaction: 2HA- H 2 A + A 2- K eq = K a2 /K a1 pH = pK a1 + pK a2 2 Henderson-Hasselbalch Equation Polyprotic acid...
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