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Topic: Mixture of weak base and weak acid equation.  (Read 2092 times)

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Offline sterlinski

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Mixture of weak base and weak acid equation.
« on: October 08, 2015, 11:32:45 AM »
Hi,
could anyone derive a formula on the bottom, please?

[A-]=[BH+], because [OH-] and [H+] << [A-] and [BH+]

Don't mind this polish words :P
Thanks a lot.

Offline Borek

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Re: Mixture of weak base and weak acid equation.
« Reply #1 on: October 08, 2015, 12:08:28 PM »
Have you tried? Solve Ka definition for [A-] and plug it into the [A-]=[BH+]...
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Offline sterlinski

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Re: Mixture of weak base and weak acid equation.
« Reply #2 on: October 08, 2015, 12:25:40 PM »
Have you tried? Solve Ka definition for [A-] and plug it into the [A-]=[BH+]...

Yes I've tried many times but I can't gain this final formula. So… Ka*[HA]/[H+]=[BH+], and then i can plug [BH+]=cB-[B ] or solved Kb definition for [BH+]. And I really don't know what to do then.

Offline Borek

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Re: Mixture of weak base and weak acid equation.
« Reply #3 on: October 08, 2015, 05:39:52 PM »
I got the same they did.

Many ways to skin that cat. Plug [HA]=CA-[A-] and [B]=CB-[HB+] into KHA and KHB, solve for [A-] and [HB+], plug into [A-]=[HB+], rearrange.
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Offline sterlinski

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Re: Mixture of weak base and weak acid equation.
« Reply #4 on: October 09, 2015, 04:24:31 PM »
Yeah, I see now, thanks a lot. :)

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