The Hg/HgO reference electrode is mostly recommended for an alkaline medium due to the electrode’s 1M filling solution (KOH or NaOH). To begin, the half-cell reaction that occurs in the Hg/HgO electrode is shown below:
In an alkaline medium, the internal and external electrolytes will have similar ions(OH_) and concentration(1M), due to which liquid junction potential will be lowered at the Hg/HgO reference electrode frit. As a result, the reference electrode potential does not vary significantly.
Pros and cons of Hg/HgO reference electrode:
- It can withstand temperatures less than 90°C.
- Not recommended for acidic conditions because HgO is easily soluble in an aqueous medium, especially at low pH < 4.
