Klarinet Archive - Posting 000281.txt from 1999/12

From: Dave Sandusky <daves@-----.com>
Subj: Re: [kl] definition of pH
Date: Sat, 11 Dec 1999 00:06:25 -0500

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Minor detail guys...pH is equal to the negative log (base ten) of the
hydronium ion activity, which is not, strictly speaking, the same as the
concentration (especially at the extremes). Enough chemistry for one day!

Dave S.

"W. Edinger" wrote:

> Roger Shilcock wrote, regarding the pH of pure water:
>
> "It's supposed to be 7.0 - that's the index (with sign changed) of the
> square root of the dissociation constant of pure water (H2O -> H+ + OH-)
>
> <-
>
> (Isn't it??)"
>
> Well, actually, no, it isn't, and I resisted boring people with this
> earlier. But since you asked (and you were actually so darned close):
>
> pH (which stands for "potential of Hydrogen") is defined as the negative
> log of the concentration of hydronium ions in a solution. The
> ionization (=dissociation) constant of pure water is 10e-14 ("ten to the
> minus 14"), and when half of the ions are H+ (the other half being OH-),
> they associate with the main water molecules as hydronium ions. That
> would be half of 10e-14, or 10e-7, the negative log of that being 7.0.
> And that's as far as I'm going with this one (unless someone begs for
> more).
>
> Bill Edinger
>
> --
> ****************************
> "Music and wine are one."
>
> - Ralph W. Emerson
>
> "Music and chemistry aren't even close."
>
> - W. Edinger
>
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