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question on buffering a solution

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4 replies to this topic

#1 jangajarn



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Posted 12 July 2010 - 08:24 AM

Hey all,
Say I am bringing up a solution (ex: Tris) to a certain pH, say 7.5 with HCl, and accidentally the pH overshoots to 7.0, or even 6.5. Would it OK if I add NaOH to bring the pH up to 7.5? I've read somewhere that whenever the pH overshoots, throw away the buffer and re-make it fresh. What are your opinions? People said that it totally depends upon the buffer. What is the conceptual difference?

#2 pito



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Posted 12 July 2010 - 08:38 AM

Pff, as far as I know we always work with HCl and NaOH to adjust the buffer and it happens more then not that you need to add some NaOH or HCl because you added to much of NaOH or HCl at the start....

Normally it shouldnt matter because you neutralise one with the other one.

If you don't know it, then ask it! Better to ask and look foolish to some than not ask and stay stupid.

#3 mdfenko


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Posted 12 July 2010 - 10:56 AM

it depends on whether your system can tolerate salt (nacl) formed by adjusting with naoh.

if you can't tolerate salt and you overshoot then you can add more tris base, titrate then adjust to the new final volume.

you can also just use equimolar tris base and tris-hcl to prepare the buffer (final volume doesn't matter).
talent does what it can
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#4 hobglobin


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Posted 12 July 2010 - 11:00 AM

For normal needs some adjustment with NaOH should be okay, as pito wrote. Finally it depends how much salt (NaCl) your system can cope with, more sensitive reactions and proteins may suffer more early.

oh mdfenko already answered it perfectly...anyway it's a matter of empiricism, i.e. try it out...

Edited by hobglobin, 12 July 2010 - 11:06 AM.

One must presume that long and short arguments contribute to the same end. - Epicurus
...except casandra's that did belong to the funniest, most interesting and imaginative (or over-imaginative?) ones, I suppose.

#5 jangajarn



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Posted 12 July 2010 - 06:42 PM

you veterans are awesome :lol: . thanks for sharing your knowledge with everybody!

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