Lecture 19 10/17/05. Principal species CasePrincipal species pH < pK a1 H2AH2A pK a1 < pH < pK a2 HA - pH > pK a2 A-A-

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Lecture 19 10/17/05

Principal species

CasePrincipal species pH < pK a1 H2AH2A pK a1 < pH < pK a2 HA - pH > pK a2 A-A-

Fractional composition

p. 217

Desired pH vs. pK How many mL of 0.8 M KOH should be added to moles oxalic acid (FW g/mol) to give a pH of 4.40 when diluted to 500 mL. pK a1 = 1.252H 2 Ox  HOx - + H + pK a2 = 4.266HOx -  Ox -2 + H +

Triprotic Acids H 3 A: Treat as monoprotic acid H2A-:H2A-: HA 2- : A 3- : Treat as monobasic

Isoionic point pH when HA (neutral zwitterion) is dissolved in water

Isoelectric point