Precipitate (mercury compound)

Precipitate (Latin for "excretion") is an outdated term for some mercury compounds. The fusible and infusible precipitate are names for two mercury - complex compounds . The terms red and yellow precipitate both stand for mercury (II) oxide .

The colorless fusible precipitate is a mercury (II) ammine complex, diammine mercury (II) chloride [Hg (NH ₃ ) ₂ ] Cl ₂ with a melting point of 300 ° C. The complex is formed when mercury (II) chloride is mixed with gaseous ammonia .

${\displaystyle \mathrm {HgCl_{2}+2\ NH_{3}\longrightarrow [Hg(NH_{3})_{2}]Cl_{2}} }$

Formation of the fusible precipitate by reaction of mercury (II) chloride with gaseous ammonia

In the salt-like complex compound, the cation [H ₃ N — Hg — NH ₃ ] ^{2+, which is} quite stable even in acidic solutions, is present in a linear structure.

The colorless, infusible precipitate is a mercury (II) amido chloride, [HgNH ₂ ] _n Cl _n . It is formed when mercury (II) chloride reacts with ammonia water .

${\displaystyle \mathrm {HgCl_{2}+2\ NH_{3}\longrightarrow [Hg(NH_{2})]Cl\ +\ NH_{4}Cl} }$

Formation of the infusible precipitate by the reaction of mercury (II) chloride with ammonia water

The infusible precipitate consists of angled [(HgNH ₂ ) _n ] ^{n +} chains, with N — Hg — N bonds forming linear segments.

The connection is also formed when mercury (I) chloride (Hg ₂ Cl ₂ , also called calomel) is poured with ammonia. This creates a black precipitate, as finely divided, elemental mercury is also deposited. This reaction is an important proof of Hg ₂ ²⁺ ions:

${\displaystyle \mathrm {Hg_{2}Cl_{2}\ +\ 2\ NH_{3}\longrightarrow \ Hg\ +\ [Hg(NH_{2})]Cl\downarrow \ +\ NH_{4}Cl} }$

infusible precipitate as a product of the calomel reaction with ammonia

The two forms of mercury (II) oxide are referred to as red precipitate and yellow precipitate . The colors are due to different grain sizes and lattice defects. In nature, the red precipitate is represented as the mineral montroydite .

Individual evidence

1. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 91st – 100th, improved and greatly expanded edition. Walter de Gruyter, Berlin 1985, ISBN 3-11-007511-3 , p. 1050.
2. ^ Entry on mercury (II) oxide in the GESTIS substance database of the IFA , accessed on October 6, 2008 (JavaScript required)