Mercury(I) chloride

Mercury(I) chloride, also known as calomel and mercurous chloride, is a chemical compound made of mercury and chlorine. It has the chemical formula . It has one mercurous cation  and two chloride anions.

Properties
It is a white to pale yellow crystalline solid. It is toxic, but not as toxic as mercury(II) chloride because it does not dissolve in water. It turns back into mercury and mercury(II) chloride when reacted with ammonia or exposed to ultraviolet light. The black color that came from the reaction with ammonia gave its name "calomel" (beautiful black). It is a weak reducing agent. It is the most common mercury(I) compound.

Occurrence
Calomel is sometimes found as a mineral, but it is quite rare.

Preparation
It is made by reacting mercury with mercury(II) chloride. It can also be made by reacting mercury(I) nitrate with sources of chloride, such as sodium chloride. 

Uses
It is used in electrochemistry as a reference electrode. Reference electrodes are used to find the electrode potentials (ability to be oxidized and reduced) of other chemical substances. Since it decomposes when light is shined on it, it is used to see how many photons are in a light beam. It was used as medicine in the past, although it was toxic.

Related pages
Electrolysis
Mercury(II) oxide
Mercury(I) bromide

Category:Mercury compounds
Category:Chloride salts