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Topic: pKa-values  (Read 5147 times)

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Offline Kork

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pKa-values
« on: March 21, 2012, 12:18:50 PM »
How can a compound have 2 pKa-values?

Im working with glycerole-3-phosphate which have two pKa-values 2,15 and 7,2. How can it have two Pka-values. And how do I figure which kind of the compound there will be if it's put in a solution with pKa=4?

Offline sjb

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Re: pKa-values
« Reply #1 on: March 21, 2012, 12:23:57 PM »
How can a compound have 2 pKa-values?

Im working with glycerole-3-phosphate which have two pKa-values 2,15 and 7,2. How can it have two Pka-values. And how do I figure which kind of the compound there will be if it's put in a solution with pKa=4?

What is the definition of pKa?

Offline Borek

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Re: pKa-values
« Reply #2 on: March 21, 2012, 12:26:15 PM »
If it is diprotic it has two pKa's, if it is triprotic it has three, if it is tetraprotic it has four and so on.

I guess you mean pH=4, not pKa=4, as pKa is not a property of a solution, but of the substance.

Knowing pH and Ka (pKa) you can calculate relative concentrations of acid and conjugate base, it requires just a simple rearranging of a dissociation constant.
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Offline Kork

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Re: pKa-values
« Reply #3 on: March 21, 2012, 01:28:26 PM »
yes i mean pH=4 will it be protonated´? why?

Offline Borek

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Re: pKa-values
« Reply #4 on: March 21, 2012, 01:57:29 PM »
yes i mean pH=4 will it be protonated´? why?

What do you mean by "it"? Do you understand that "protonated" in the case of diprotic acid is ambiguous?
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Offline Kork

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Re: pKa-values
« Reply #5 on: March 21, 2012, 02:37:37 PM »
how do I figure which kind of the compound there will be if it's put in a solution with pH=4?

this is what my teacher asked!

Offline Borek

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Re: pKa-values
« Reply #6 on: March 21, 2012, 02:42:36 PM »
What species are present in the solution of diprotic acid H2A?
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