Theory of Indirect Coulometry

In electrolytic processes involving constant current, the generating electrode will eventually become concentration polarised. This can result in a shift in the potential at the electrode and the possibility of a reaction occurring other than that intended This will cause less than 100 percent current efficiency for the 

For the 0.001 M Ce, the application of a constant current at i2 will cause Ce + to be reduced at the cathode to Ce3+ until the value of [Ce +] reaches about 

0005 M. At this point, because of concentration polarisation, Ce ions can no longer reach the electrode surface fast enough to sustain the constant current demand of 12. The cathode potential will therefore drift rapidly to more negative values until it reaches -0.50 V, at which point hydrogen ion is discharged and the current i2 is sustained. The current efficiency for Equation (58) is no longer 100 percent, and the method can not provide a quantitative determination of Ce. 

The [Fe3+] remains constant and u remains constant as long as the solution contains Ce +. The net reaction results in 100 percent efficiency for the reduction of 00 + under conditions of one equivalent of Ce reduced for every faraday (96,516 C) passed through the solution. 

This type of situation is apphed on some occasions in coulometric titration, and the following points are important. 

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