Led Indication; Taking Redox Measurements - Hanna Instruments HI 8510 Instruction Manual

LED INDICATION

All LEDs above the keys indicate the state of
each function, whether it is active or the
display is indicating the mode.
For HI 8711 only
Each LED can be in one of the following
states:
A) Light on The mode is displayed
on the LCD but is not
active, e.g. the alarm
setpoint is displayed but
the alarm contact is
open.
B) Light blinking 25% on, 75% off
The mode is not dis-
played but it is active,
e.g. the alarm contact
is closed but the alarm
setpoint is not displayed.
C) Light blinking 75% on, 25% off
The mode is active and
being displayed.
D) Light off The function is neither
active nor displayed.
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Redox measurements allow the quantifica-
tion of the solution oxidizing/reducing power,
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 any chemical reaction.
The most common ORP electrodes are
provided with gold or platinum surfaces; gold
features a higher resistance than platinum in
conditions of strong oxidation, while platinum
is preferred for measuring oxidizing solutions
containing halides, and for general purposes.
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.
To make correct redox measurements, it is
necessary that the surface of the electrode is
clean and smooth, and that a preventive
treatment is performed.
Because the Pt/PtO system depends on the
solution pH level, the electrode pre-treatment
may be determined by the pH and the redox
potential of the solution to be measured.
40£

TAKING REDOX MEASUREMENTS

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