Taking Redox Measurements - Hanna Instruments HI 8510 Series Instruction Manual

TAKING REDOX MEASUREMENTS

Redox measurements allow the quantifica-
tion of the oxidizing or reducing power of a
solution, and are commonly expressed in
mV.
Oxidation may be defined as the process
during which a molecule (or an ion) loses
electrons and reduction as the process by
which electrons are gained.
Oxidation is always coupled together with
reduction so that as one element gets oxi-
dized, the other is automatically reduced,
therefore the term oxidation-reduction is fre-
quently used.
Redox potentials are measured by an elec-
trode capable of absorbing or releasing elec-
trons without causing a chemical reaction
with the elements with which it comes into
contact.
The electrodes most usually available for this
purpose have gold or platinum surfaces; gold
possesses a higher resistance than platinum
in conditions of strong oxidation, while plati-
num is preferred for the measurements of
oxidizing solutions containing halides and for
more general uses.
When a platinum electrode is immersed in an
oxidizing solution a monomolecular layer of
oxygen is developed on its surface. This layer
does not prevent the electrode from function-
ing, but it increases the response time. The
opposite effect is obtained when the platinum
surface absorbs hydrogen in the presence of
reducing mediums. This phenomenon is rough
on the electrode.
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