# Mercury coulometer

Mercury coulometer is an electroanalytical chemistry device using mercury to determine the amount of matter transformed (in coulombs) during the following reaction:

Hg2+ + 2e = Hgo[1]

These oxidation/reduction processes have 100% efficiency with the wide range of the current densities. Measuring of the quantity of electricity (coulombs) is based on the changes of the mass of the mercury electrode. Mass of the electrode can be increased during cathodic deposition of the mercury ions or decreased during the anodic dissolution of the metal.

${\displaystyle Q={\frac {2\Delta mF}{M_{\rm {Hg}}}}}$,

where

Q, quantity of electricity;
${\displaystyle \Delta \ m}$, mass changes;
${\displaystyle M_{\rm {Hg}}}$, the molar mass of mercury