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Calomel is a mercury chloride mineral with formula Hg 2 Cl 2 (see mercury(I) chloride). It was used as a medicine from the 16th to early 20th century, despite frequently causing mercury poisoning in patients.
Mercury(I) chloride is the chemical compound with the formula Hg 2 Cl 2. Also known as the mineral calomel [4] (a rare mineral) or mercurous chloride, this dense white or yellowish-white, odorless solid is the principal example of a mercury(I) compound. It is a component of reference electrodes in electrochemistry. [5] [6]
The saturated calomel electrode (SCE) is a reference electrode based on the reaction between elemental mercury and mercury(I) chloride. It has been widely replaced by the silver chloride electrode , however the calomel electrode has a reputation of being more robust.
Internal electrode, usually silver chloride electrode or calomel electrode. Internal solution, usually a pH=7 buffered solution of 0.1 mol/L KCl for pH electrodes or 0.1 mol/L MCl for pM electrodes. When using the silver chloride electrode, a small amount of AgCl can precipitate inside the glass electrode.
Mercury(I) oxide, also known as mercurous oxide, is an inorganic metal oxide with the chemical formula Hg 2 O. It is a brown/black powder, insoluble in water but soluble in nitric acid. With hydrochloric acid, it reacts to form calomel, Hg 2 Cl 2. [4] Mercury(I) oxide is toxic but without taste or smell.
It arises from the reaction of mercury(II) chloride and ammonia (Calomel reaction), where the resulting mercuric amidochloride is highly insoluble. It forms white crystals in the shape of small prisms. It tastes earthy and metallic, but is a deadly poison and should not be ingested. [2]
The most common types of reference electrodes used in analytical chemistry include the standard hydrogen electrode, the saturated calomel electrode, and the Ag/AgCl electrode. [3] The standard hydrogen electrode (SHE) is the primary reference electrode that has a potential of 0 volts at all temperatures and a pressure of 1 atm.
Potentiometric titrations were first used for redox titrations by Crotogino. He titrated halide ions with potassium permanganate using a shiny platinum electrode and a calomel electrode. He said that if an oxidizing agent is added to a reducing solution then the equilibrium between the reducing substance and reaction product will shift towards ...