Kalomelelektrodit

Kalomelelektrodit, or calomel electrodes, are a type of reference electrode widely used in electrochemistry. They consist of mercury in contact with mercurous chloride (calomel), which is itself in contact with a solution containing chloride ions. This specific arrangement creates a stable and reproducible potential, making the calomel electrode a reliable standard against which the potential of other electrodes can be measured. The electrochemical reaction involved is: Hg(l) + Cl-(aq) <=> 1/2 Hg2Cl2(s) + e-.

The calomel electrode is typically constructed with a glass tube containing mercury at the bottom. Above the mercury layer is a paste of calomel and mercury, saturated with potassium chloride (KCl). The KCl solution serves as the electrolyte and establishes electrical contact with the test solution through a porous plug or a salt bridge. The concentration of KCl used affects the electrode's potential; common concentrations are saturated, 1 M, or 0.1 M. A saturated KCl solution provides the most stable potential but is more prone to contamination.

The primary advantage of the calomel electrode is its stability and ease of construction. It is less susceptible to variations in pH compared to some other reference electrodes. However, it contains mercury, a toxic heavy metal, which limits its use in certain applications and requires careful handling and disposal. It can also be affected by high temperatures or the presence of strong oxidizing or reducing agents. Despite these limitations, the calomel electrode remains a valuable tool in analytical chemistry and electrochemical research for determining potentials in aqueous solutions.