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From: Lois Goldthwaite (loisg_at_[hidden])
Date: 2001-06-29 19:56:04

> -----Original Message-----
> From: Deane_Yang_at_[hidden] [mailto:Deane_Yang_at_[hidden]]
> Sent: Friday, 29 June 2001 3:23 AM

> There are logarithmic units such as decibels and pH. I'm not familiar
> with how these are used in formulas. I think these are sufficiently
> strange so that they should be treated specially.

It's been a long time since I took high school chemistry, but I do
remember that the pH number is the negative exponent of the hydrogen ion
concentration. In a bottle of pure distilled water (no electrolytes
present), a small number of H20 molecules break up into
electrically-charged ions of hydrogen (H) and hydroxide (OH). The number
of these particles is called the "ionization constant" of pure water and
is approximately (meaning some constant multiplied by) 10 to the minus
14th power, or 10 to the minus 7th H+ ions times 10 to the minus 7th OH-
ions per liter, or gram molecular weight, or anyway some
quantity of water. Distilled water has a pH of 7 (because H+ is 10^-7,

If you add acid to the water then that creates more H+ ions and some of
the OH- ions combine with the now-more-prevalent H+ ions and become
water molecules again so there are relatively more H+ ions floating
around in the soup. So if there are now 10^-3 H+ ions and 10^-11 OH-
ions, the solution has a pH of 3, which is acidic.

If you add some basic chemical to the soup, that increases the number of
OH- ions and decreases the H+ concentration, so the pH goes to somewhere
between 7 and 14, ergo basic instead of acidic.

I feel quite pleased that I have finally found a way to use this bit of
information after all these years. :-) The only other thing I remember
from high school chemistry is Avogadro's constant, 6.02252 x 10^23, so
I'll mention that also in passing.

Now if I could only remember some high school math so I could follow the
rest of this discussion ....


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