Coulometric Titration
Definition and meaning of Coulometric Titration in chemistry.
Coulometric titration is an electroanalytical method in which the titrant is generated in situ at a constant current by electrolysis of a suitable precursor in the sample solution, and the amount of analyte is calculated from the quantity of electricity (charge) needed to reach the endpoint, rather than from a measured volume of standard titrant.
In more detail
Because the electrogenerated titrant reacts with the analyte as fast as it forms, applying a constant current I for a measured time t gives the charge Q = I·t, and Faraday's laws convert Q directly into moles of titrant (and hence analyte) generated, with no need to standardize a titrant solution. The endpoint is usually detected potentiometrically or amperometrically (e.g., biamperometrically), which stops the current or starts a timer for back-titration correction. The method achieves very high precision and can generate unstable or hazardous titrants (I2, Br2, Ag+, H+/OH-) safely and in small, exact amounts, making it ideal for micro- and trace-level analysis such as Karl Fischer water determination.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Governing law | Faraday's laws of electrolysis |
| Key relation | Q = I × t (constant current), n = Q/(zF) |
| Common application | Karl Fischer coulometric water determination |
Karl Fischer coulometric titration for trace water: iodide in the reagent is oxidized at the anode to generate iodine at a constant current; the iodine reacts stoichiometrically with water (via sulfur dioxide and a base), and the charge passed until a biamperometric endpoint signals complete consumption of water gives the water content directly from Faraday's law, without ever preparing a standardized iodine solution.
Frequently asked questions
How does coulometric titration differ from classical volumetric titration?
In volumetric titration a standardized titrant solution is added from a buret and volume is measured; in coulometric titration the titrant is generated electrochemically inside the cell and the charge passed (measured via current and time) replaces volume as the quantity used to calculate moles of analyte.
How is the endpoint detected in coulometric titration?
Commonly by potentiometry (a sensing electrode pair) or biamperometry (dual polarized electrodes), which halts the generator current once the analyte is fully consumed.