Topic: effect of NaCl on pH of Tris-HCl buffer (Read 7115 times)

shawnkmchen · « **on:** September 14, 2012, 05:41:32 AM »

I made a 5 mM Tris-HCl buffer at pH 7.86. When I add NaCl stock solution gradually, the pH was increased also. With ionic strength of up to 1 M, the pH was increased to 8.15. Does anyone understand the mechanism of this undesired pH increase? Many Thanks!

Borek · « **Reply #1 on:** September 14, 2012, 06:06:22 AM »

Ionic strength changes means changes to ion activities, that shifts equilibrium and changes pH, nothing unusual. For low ionic strength (say up to 0.1) effects can be relatively easily calculated, for higher ionic strengths it is easier to experimentally adjust the buffer pH than to calculate.

shawnkmchen · « **Reply #2 on:** September 14, 2012, 11:35:41 AM »

Quote from: Borek on September 14, 2012, 06:06:22 AM

Ionic strength changes means changes to ion activities, that shifts equilibrium and changes pH, nothing unusual. For low ionic strength (say up to 0.1) effects can be relatively easily calculated, for higher ionic strengths it is easier to experimentally adjust the buffer pH than to calculate.

Thanks for your explanation. Then, if I increase the ionic strength and want to maintain the pH, what can I do?

Borek · « **Reply #3 on:** September 14, 2012, 12:37:34 PM »

As I wrote - stick a pH electrode into the mixture and adjust pH adding base or acid.

shawnkmchen · « **Reply #4 on:** September 14, 2012, 10:24:08 PM »

Quote from: Borek on September 14, 2012, 12:37:34 PM

As I wrote - stick a pH electrode into the mixture and adjust pH adding base or acid.

Oh, I see. Thanks for your kind help and quick reply.

Topic: effect of NaCl on pH of Tris-HCl buffer (Read 7115 times)

shawnkmchen

effect of NaCl on pH of Tris-HCl buffer

Borek

Re: effect of NaCl on pH of Tris-HCl buffer

shawnkmchen

Re: effect of NaCl on pH of Tris-HCl buffer

Borek

Re: effect of NaCl on pH of Tris-HCl buffer

shawnkmchen

Re: effect of NaCl on pH of Tris-HCl buffer

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