The voltage at the equivalence point resulting from the half-cell reactions described by Equations 7.41(15) and (21) can now be computed. Since this system is unsym-metrical, i.e., n1 electrons are transferred in one half-cell reaction and n2 electrons are transferred by the other half-cell reaction, the following equation gives the voltage at the equivalence or endpoint:
n1(Emeter)CN + n2(Emeter)C
A typical value of the ORP control setpoint is +0.400 V, which is beyond the equivalence point value indicating the elimination of CN-. Once the cyanate is undergoing destruction, the following equation gives the operative half-cell reaction:
which has a standard potential of +0.89V. When the reaction is controlled at pH = 9, the half-titration voltage of reaction in Equation 7.41(24) can be estimated as follows:
The equivalence voltage of the half-cell reaction pair, Equations 7.41(21) and (24), is estimated from the halftitration voltages as follows:
For cyanate destruction, the normal control point is about +0.600 V.
Figure 7.41.2 shows the reactions from cyanide to cyanate to cyanate destruction in titration form. The re-
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