4 Acids and bases: oxidation and reduction
oxidation and
reduction
These topics, which are more fully treated in texts on physical
chemistry, require some consideration here, because the terms 'acid',
'base', 'oxidation' and 'reduction' are used so widely in inorganic
chemistry.
PHOTONIC ACIDS AND BASES
An acid was once defined simply as a substance which produces
hydrogen ions, or protons. However, the simple proton, H"^1 ", is
never found under ordinary conditions, and this definition required
amendment. Br0nsted and, independently, Lowry, therefore re-
defined an acid as a susbstance able to donate protons to other
molecules or ions, and a base as a substance capable of accepting
such protons. If we consider hydrogen chloride, HC1, as an example,
the HC1 molecule is essentially covalent, and hydrogen chloride (gas
or liquid) contains no protons. But anhydrous hydrogen chloride
in benzene will react with anhydrous ammonia:
HC1 + NH 3 -> NH^Cr
Here, clearly, a proton is donated to the ammonia, which is the
base, and hydrogen chloride is the acid. In water, the reaction of
hydrogen chloride is essentially
HC1 + H 2 O^H 3 O+ + Cl"
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