Silver chloride


Silver chloride is a chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water. Upon illumination or heating, silver chloride converts to silver, which is signaled by grey to black or purplish coloration to some samples. AgCl occurs naturally as a mineral chlorargyrite.

Preparation

Silver chloride is easily synthesized by combining aqueous solutions of silver nitrate and sodium chloride.
It can also be produced by reacting silver nitrate with cobalt chloride. This precipitation is general for silver nitrate's reaction with soluble chloride salts and is not unique simply to cobalt.

Structure and reactions

The solid adopts the fcc NaCl structure, in which each Ag+ ion is surrounded by an octahedron of six chloride ligands. AgF and AgBr crystallize similarly. However, the crystallography depends on the condition of crystallization, primarily free silver ion concentration, as is shown on the pictures left. AgCl dissolves in solutions containing ligands such as chloride, cyanide, triphenylphosphine, thiosulfate, thiocyanate and ammonia. Silver chloride reacts with these ligands according to the following illustrative equations:
Silver chloride does not react with nitric acid.
Most complexes derived from AgCl are two-, three-, and, in rare cases, four-coordinate, adopting linear, trigonal planar, and tetrahedral coordination geometries, respectively.
Above 2 reactions are particularly important in qualitative analysis of AgCl in labs as AgCl is white in colour, which changes to Ag3AsO3 which is yellow in colour or Ag3AsO4 which is reddish brown in colour.

Chemistry

In one of the most famous reactions in chemistry, addition of colorless aqueous silver nitrate to an equally colorless solution of sodium chloride produces an opaque white precipitate of AgCl:
This conversion is a common test for the presence of chloride in solution. Due to its conspicuousness it is easily used in titration, which gives the typical case of argentometry.
The solubility product, Ksp, for AgCl in water is at room temperature, which indicates that only 1.9 mg of AgCl will dissolve per liter of water. The chloride content of an aqueous solution can be determined quantitatively by weighing the precipitated AgCl, which conveniently is non-hygroscopic, since AgCl is one of the few transition metal chlorides that is unreactive toward water. Interfering ions for this test are bromide and iodide, as well as a variety of ligands. For AgBr and AgI, the Ksp values are 5.2 x 10−13 and 8.3 x 10−17, respectively. Silver bromide and silver iodide are also significantly more photosensitive than is AgCl.
AgCl quickly darkens on exposure to light by disintegrating into elemental chlorine and metallic silver. This reaction is used in photography and film.

Uses