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The aqueous phase in contact with the mercury and the mercury(I) chloride (Hg 2 Cl 2, "calomel") is a saturated solution of potassium chloride in water. The electrode is normally linked via a porous frit (sometimes coupled to a salt bridge) to the solution in which the other electrode is immersed. In cell notation the electrode is written as:
The overall chemical reaction taking place in a cell is made up of two independent half-reactions, which describe chemical changes at the two electrodes. To focus on the reaction at the working electrode , the reference electrode is standardized with constant (buffered or saturated) concentrations of each participant of the redox reaction.
Calomel is used as the interface between metallic mercury and a chloride solution in a saturated calomel electrode, which is used in electrochemistry to measure pH and electrical potentials in solutions. In most electrochemical measurements, it is necessary to keep one of the electrodes in an electrochemical cell at a constant potential.
A typical modern pH probe is a combination electrode, which combines both the glass and reference electrodes into one body. The combination electrode consists of the following parts (see the drawing): A sensing part of electrode, a bulb made from a specific glass. Internal electrode, usually silver chloride electrode or calomel electrode.
The working electrode is the semiconductor material and the electrolyte is composed of a solvent, an electrolyte and a redox specie. A UV-vis lamp is usually used to illuminate the working electrode. The photoelectrochemical cell is usually made with a quartz window because it does not absorb the light.
In electrochemistry, cell notation or cell representation is a shorthand method of expressing a reaction in an electrochemical cell.. In cell notation, the two half-cells are described by writing the formula of each individual chemical species involved in the redox reaction across the cell, with all other common ions and inert substances being ignored.
Reference electrodes generally used are hydrogen electrodes, calomel electrodes, and silver chloride electrodes. The indicator electrode forms an electrochemical half-cell with the interested ions in the test solution. The reference electrode forms the other half-cell. The overall electric potential is calculated as
A bulk electrolysis is best performed in a three part cell in which both the auxiliary electrode and reference electrode have their own cell which connects to the cell containing the working electrode. This isolates the undesired redox events taking place at the auxiliary electrode.