Klarinet Archive - Posting 000268.txt from 1999/12

From: "W. Edinger" <wde1@-----.com>
Subj: [kl] definition of pH
Date: Sat, 11 Dec 1999 00:06:12 -0500

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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