horiba U-51, Инструкция по эксплуатации

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6 Reference
116
When only one type of state of equilibrium uniquely by equation (Fe
3+
) and the reductant
(Fe
2+
) (using the equation a
Fe
2+
/ a
Fe
3+
). Actually, however many kinds of states of equilibrium
exist simultaneously between various kinds of ions, in most solutions. This means that under
actual circumstances, ORP cannot be expressed using the simple equation shown above and
that the physical and chemical significance with respect to the solution is not very clear.
In this respect, the value of ORP must be understood to be only one indicator of the property
of a solution. The measurement of ORP is widely used, however, as an important index in the
analysis of solutions (potentiometric titration) and in the waste water treatment.
6.11.2 Standard electrode (reference electrode) types and ORP
The ORP is obtained comparing with corresponding reference electrode employed.
If different kinds of reference electrodes are used for measurement, the ORP value of the
same solution may appear to be different. HORIBA Advanced Techno’s reference electrode
uses Ag/AgCl with 3.33 mol/L KCl as inner solution. According to general technical literature,
normal hydrogen electrodes (N.H.E.) are often used as the standard electrode.
The relationship between N.H.E. and the ORP that is measured using an Ag/AgCl with 3.33
mol/L KCl electrode is expressed by the following equation.
E
N.H.E.
= E + 206

0.7(t

25) mV t = 0 - 60

C
E
N.H.E.
: Measured ORP value using N.H.E. as the reference electrode
E: Measured ORP value using Ag/AgCl with 3.33 mol/L KCl as the reference electrode
Potential sign
Standard ORP is expressed in the following way, in literature related to electrochemistry and
analytical chemistry.
However, in some literature, the "+" and "-" signs are reversed.
In expressions like B, above, the reaction is just reversed and there is no essential difference.
But this kind of expression does invite confusion. The majority of the world, today, is
consistent in its use of the signs as they are used in A, above.
For this reason, HORIBA Advanced Techno, too, uses signs concerning ORP that are
consistent with A, above.
A
Li
+
+ e
－
→ Li
E
0
=

3.024 V VS N.H.E.
B
Li → Li
+
+ e
－
E
0
=

3.024 V VS N.H.E.