Question

What is the construction and working of dropping mercury electrodes?

Answer 1

Dropping mercury electrode:

• The dropping mercury electrode (DME) is a working electrode that is made up of mercury.

Construction of DME:

It is made up of three components:

• Capillary
• Mercury reservoir vessel
• Standing tube with adjacent stopcock

Working of DME:

• The dropping mercury electrode (DME) is polarizable and can act as an anode as well as a cathode.
• The pool of mercury acts as a counter electrode, i.e., it will act as an anode if DME is the cathode or vice-versa.
• The counter electrode is non-polarizable. To the analyte solution placed in a glass beaker, supporting electrolyte such as $\mathrm{KCl}$ is added.
• Pure nitrogen/hydrogen gas is bubbled through the solution, to take out oxygen.
• Then gradually increasing voltage is applied to the polarographic cell, typically by going to a more negative decomposing potential and current is recorded.