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.

Coulometry uses the amount of electrical charge needed to fully electrolyze an analyte, to determine its quantity without requiring any analytical standards.

The total charge that is passed during electrolysis is related to the amount of analyte by Faraday's laws of electrolysis.

For efficient coulometric measurements, a charge equivalent to Faraday's constant multiplied by the number of electrons involved in the relevant half-reaction must be supplied per mole of the analyte transformed at the electrode.

Coulometric methods employ either a constant current or a controlled potential.

Constant-current coulometry measures the amount of charge passing through the cell over time while applying a constant current to the system.

In controlled-potential coulometry, a constant potential is applied to the system, and the amount of charge passed through the cell is measured as the current varies over time.