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Topic: pH calculation for an amino acid solution  (Read 7385 times)

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Offline MrSynth

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pH calculation for an amino acid solution
« on: April 22, 2011, 01:24:34 AM »
I realize that perhaps this should go in the "general chemistry" section, since it involves the calculation of pH, but it does deal with amino acids, so I thought I'd take a chance and put it here.

I'm asked to calculate the pH of a 1.0 M solution of alanine. I'm given that alanine's two acid dissociation constants are 2.34 for the protonated form going to the neutral form (which is really the zwitterion form) and 9.69 for the neutral form going to the deprotonated form.

Can someone please show me how to do this? I'm confusing myself the more I look at the problem.

Offline Kadabrium

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Re: pH calculation for an amino acid solution
« Reply #1 on: April 23, 2011, 06:48:57 AM »
if you mean it's hydrochloride of it that's equal to a diprotic acid with Ka1>>Ka2..so just use Ka1
if it‘s in free form that's a mixture of 1M base B and 1M acid HA, use these equations [HB+]+[H+]=[A-]+[OH-] and [HA]+[A-]=[HB+]+=1M as well as Ka1, Ka2, Kw to solve..

Offline AWK

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Re: pH calculation for an amino acid solution
« Reply #2 on: April 26, 2011, 03:06:20 AM »
If you hane pure alanine - approximate pH=1/2(Ka1+pKa2). This can be affected by a ionic strength of this solution by ~ +0.15 pH unit
AWK

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