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Prove/show that K(a1)=Kw/K(b3) for a triprotic acid?
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Topic: Prove/show that K(a1)=Kw/K(b3) for a triprotic acid? (Read 4047 times)
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SheffieldWednesday4ever
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Prove/show that K(a1)=Kw/K(b3) for a triprotic acid?
«
on:
December 06, 2010, 11:05:10 PM »
Hi, this is one of the questions I'm trying to figure out.
So far, I've written the dissociations:
H3A
H + H2A
-
K(a1)
H2A
-
H + HA
-2
K(a2)
HA
-2
H + A
-3
K(a3)
I know Kb
3
is just A
-3
+H
2
O
HA
-2
+ OH
-
which I'm stuck...
Should I bring the values to? Or just use the Products/reactants eqb?
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Borek
Mr. pH
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Re: Prove/show that K(a1)=Kw/K(b3) for a triprotic acid?
«
Reply #1 on:
December 07, 2010, 05:02:29 AM »
Write definitions of both Ka1 and Kb3. Not reactions, but definitions of dissociation constants.
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ChemBuddy
chemical calculators - stoichiometry, pH, concentration, buffer preparation,
titrations.info
SheffieldWednesday4ever
Regular Member
Posts: 38
Mole Snacks: +0/-0
Re: Prove/show that K(a1)=Kw/K(b3) for a triprotic acid?
«
Reply #2 on:
December 08, 2010, 04:36:38 AM »
Thanks, but I've done that. So:
K
a1
xK
b3
=([H][H
2
A]/[H
3
A])x([OH][HA]/[A])
So, somehow the H2A H3A HA and A must cancel to 1? Would this be done with a mass balance then? I still haven't gotten there.
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Borek
Mr. pH
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Re: Prove/show that K(a1)=Kw/K(b3) for a triprotic acid?
«
Reply #3 on:
December 08, 2010, 05:36:55 AM »
Your Kb3 is wrong.
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ChemBuddy
chemical calculators - stoichiometry, pH, concentration, buffer preparation,
titrations.info
SheffieldWednesday4ever
Regular Member
Posts: 38
Mole Snacks: +0/-0
Re: Prove/show that K(a1)=Kw/K(b3) for a triprotic acid?
«
Reply #4 on:
December 08, 2010, 11:54:07 AM »
Thanks!
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Prove/show that K(a1)=Kw/K(b3) for a triprotic acid?