From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: sci.chem
Subject: Re: Why is this pH 13+?
Date: 27 Jan 1996 06:24:13 GMT

In article <4ebkse$9fc@treasure.coastalnet.com>,
47jv59wl@coastalnet.com@abaco says:

>Can anyone explain how an aqueous solution that is 99% KNO3, NaNO2, & NaNO3
>at +400F have a pH of +13?  I have a customer who says it is.  Where are the
>-OH ions coming from?  There certainly can't be enough in the water.

Why not pH 13? If it's 99% metal nitrates and nitrites at a 
temperature nearly 200 degF above the normal boiling point
of water, it is hardly an "aqueous" solution. A high pH just
means there is little hydronium ion present. Maybe the 
hydronium figured there was no sense hanging around after 
the water left.

A high pH simply denotes a low concentration of H+. If that low
concentration of H+ occurs in water, there is a corollary
effect that the concentration OH- must go up. Your toothbrush,
however, may well contain less than 1X10^-13 moles of H+ per 
liter of melted plastic at 400 degF, but that does not imply 
that it contains a lot of hydroxyl ion.

Come to think of it, the pH of hot mercury is probably nearly
as high as that of the space in an empty beaker :)

Jerry (Ico)

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: sci.chem
Subject: Re: Why is this pH 13+?
Date: 29 Jan 1996 05:21:34 GMT

In article <4ehaid$crd@morgoth.sfu.ca>, David Naugler <dnaugler@sfu.ca> says:

>glhurst@onr.com (Gerald L. Hurst) wrote:
>
>>In article <4ebkse$9fc@treasure.coastalnet.com>,
>>47jv59wl@coastalnet.com@abaco says:
>>>
>>>Can anyone explain how an aqueous solution that is 99% KNO3, NaNO2, & NaNO3
>>>at +400F have a pH of +13?  I have a customer who says it is.  Where are the
>>>-OH ions coming from?  There certainly can't be enough in the water.
>>
>>Why not pH 13? If it's 99% metal nitrates and nitrites at a 
>>temperature nearly 200 degF above the normal boiling point
>>of water, it is hardly an "aqueous" solution.
>
>The pH of a solution is only properly defined for a truely aqueous
>system in which it can be said that [H+][OH-]=10^-14. It may be true
>that at +400F and 99% alkali nitrate and nitrite salts, we have a
>nonaqueous system. In this case, any serious student of chemical
>equilibria would throw away the concept of pH and reformulate the
>equilibrium problem in terms of the various species present and their
>free energies of formation under the conditions of temperature and
>pressure actualy obtained.
>
>It may safely be said that the concept of pH causes brain damage in
>those who fail to progress beyond first year chemistry.

You're right. I checked the pH of my melted toothbrush and empty
beaker with litmus pH paper. It turned brown in the plastic and
refused to change color in the empty beaker, so clearly the theory
does not extend to these materials. Thank you for clarifying
the matter. Now I can cancel the experiments I had planned with
the bowling ball.

Jerry (Ico)