pH of water (was: Re: Oligo stability in water at -20 C)

Dima Klenchin klenchin at facstaff.REMOVE_TO_REPLY.wisc.edu
Thu Aug 13 14:00:29 EST 1998


In article <see_sig-1308980800530001 at 192.168.0.84>, rgrant at netscape.net wrote:
:In article <6qsuau$tp6$1 at news.doit.wisc.edu>,
:klenchin at facstaff.REMOVE_TO_REPLY.wisc.edu (Dima Klenchin) wrote:
:
:: First of all not "by definition", but by dissociation constant (H+ + OH- 
:: <=> H20), 
:
:Yes, that's a working definition of neutrality.

And again you are incorrect. If the dissociation constant would be 
different, then you'd still have neutrality (equal concentrations of H+ 
and OH-) but the pH (-log[H+]) would be different. 

:: second I suggest that you measure pH in your water once and find
:: out that it is slightly acidic due to [nearly unavoidable] dissolution of 
:: CO2 in the water.
:And I say that even in a CO2-free atmosphere most pH electrodes will read
:<>7, due to the nature of the beast.

True but has nothing to do with the fact that the real water under 
consideration, the one that's relevant to the thread and the one we work 
with, is much more acidic than the error of most pH electrodes under low
buffering conditions.
:
:Go back and re-read my original post.

You stated that pH of the water if 7 "by definition". That is 
incorrect statement. First because not by definition, second because
this theoretical water does not exist in your real life. If you meant that 
_neutral_ is pH 7 by definition, then it is correct but totally 
irrelevant. 

        - Dima




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