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FIG. 7.41.1 Approximate titration curve for the Fe2+/Ce4+ system.

where n = 2. As stated in Equation 7.39(4) that [OH—][H+] = Kw = 1 X 10—14 at 25°C and —log [H+] = pH, Equation 7.41(17) can be written as follows:

0.0591 [CNO—] (Emeter) CN = —1.169 + log ^^ + 0.0591(14 — pH)

Equation 7.41(18) shows the importance of the pH in the ORP process. If the pH is unknown and controlled, the meter reading is useless. When the process is controlled at pH = 9; (Emeter)CN at the half-titration point can then be calculated as follows:

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