10.13 : Coulometry: Overview

Coulometry is one of the rapid, most accurate, and precise analytical techniques that determine the quantity of an analyte by measuring the electrical charge needed for its complete electrolysis without using any analytical standards. The total charge passed during electrolysis correlates with the analyte amount by Faraday's laws of electrolysis. For accurate coulometric measurements, a charge equal to Faraday's constant multiplied by the number of electrons involved in the relevant half-reaction must be supplied per mole of analyte transformed at the electrode. This is represented by the equation:

Total Charge (Q) = n x F

where Q is the total charge required, n is the number of electrons involved, and F (Faraday's constant) is approximately 96,485 C/mol. A current efficiency of 100% is necessary for coulometric measurements.

Coulometric methods use either constant current or controlled potential. Constant-current coulometry measures the charge passed through the cell over time while applying a constant current. In contrast, controlled-potential coulometry applies a constant potential, measuring the charge passed through the cell as the current varies over time.