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Author Topic: pKa-values  (Read 1821 times)

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Kork

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pKa-values
« on: March 21, 2012, 06:18:50 AM »

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?
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sjb

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Re: pKa-values
« Reply #1 on: March 21, 2012, 06:23:57 AM »

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?
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Borek

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Re: pKa-values
« Reply #2 on: March 21, 2012, 06:26:15 AM »

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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Kork

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Re: pKa-values
« Reply #3 on: March 21, 2012, 07:28:26 AM »

yes i mean pH=4 will it be protonated´? why?
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Borek

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Re: pKa-values
« Reply #4 on: March 21, 2012, 07:57:29 AM »

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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Kork

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Re: pKa-values
« Reply #5 on: March 21, 2012, 08:37:37 AM »

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!
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Borek

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Re: pKa-values
« Reply #6 on: March 21, 2012, 08:42:36 AM »

What species are present in the solution of diprotic acid H2A?
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