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Thiosulfate (S2O32−) is an oxyanion
Oxyanion

An oxyanion or oxoanion is a chemical compound with the generic formula AxOyz-. . Oxyanions are formed by a large majority of the chemical elements....
 of sulfur
Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
 produced by the reaction of sulfite
Sulfite

Sulfites are chemical compound that contain the sulfite ion sulfuroxygen32- ....
 ions with elemental sulfur in boiling water. Thiosulfate occurs naturally in hot springs and geysers, and is produced by certain biochemical processes. It instantly dechlorinates water, and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate is also useful in smelting silver ore, in producing leather goods, and to set dyes in textiles.






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Thiosulfate (S2O32−) is an oxyanion
Oxyanion

An oxyanion or oxoanion is a chemical compound with the generic formula AxOyz-. . Oxyanions are formed by a large majority of the chemical elements....
 of sulfur
Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
 produced by the reaction of sulfite
Sulfite

Sulfites are chemical compound that contain the sulfite ion sulfuroxygen32- ....
 ions with elemental sulfur in boiling water. Thiosulfate occurs naturally in hot springs and geysers, and is produced by certain biochemical processes. It instantly dechlorinates water, and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate is also useful in smelting silver ore, in producing leather goods, and to set dyes in textiles. Sodium thiosulfate
Sodium thiosulfate

Sodium thiosulfate , also spelled Sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Sodium2Sulfur2Oxygen3?5Hydrogen2Oxygen, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or ?hypo.?...
 was widely used to fix black and white photography negatives after the developing stage.

Thiosulfates are stable only in neutral or alkali
Alkali

In chemistry, an alkali is a Base , Ionic compound salt of an alkali metal or alkaline earth metal Chemical element. Alkalis are best known for being Base s that dissolve in water....
ne solutions, but not in acidic solutions, due to decomposition to sulfite
Sulfite

Sulfites are chemical compound that contain the sulfite ion sulfuroxygen32- ....
 and sulfur
Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
, the sulfite being dehydrated to sulfur dioxide
Sulfur dioxide

Sulfur dioxide is the chemical compound with the formula SO2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide....
:

S2O32-(aq) + 2H+(aq) ? SO2(g) + S(s) + H2O


This reaction may be used to generate a temporary aqueous suspension
Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre....
 of particles and demonstrate the Rayleigh scattering
Rayleigh scattering

Rayleigh scattering is the elastic scattering of light or other electromagnetism radiation by particles much smaller than the wavelength of the light....
 of light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 in physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
. If white light is shone from below, blue light is seen from sideways and orange from above, due to the same mechanisms that color the sky at mid-day and dusk.

Thiosulfates react with halogens differently, which can be attributed the decrease of oxidizing power down the halogen group:

2S2O32-(aq) + I2(aq) ? S4O62-(aq) + 2I-(aq)


S2O32-(aq) + 4Br2(aq) + 5H2O(l) ? 2SO42-(aq) + 8Br-(aq) + 10H+(aq)


S2O32-(aq) + 4Cl2(aq) + 5H2O(l) ? 2SO42-(aq) + 8Cl-(aq) + 10H+(aq)


Uses of thiosulfates include the dissolving of silver
Silver

Silver is a chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal....
 salt
Salt

A salt, in chemistry, is defined as the product formed from the neutralisation reaction of acids and base . Salts are ionic compounds composed of cations and anions so that the product is electrically electric charge ....
s from photographic film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the film....
. In this context, sodium thiosulfate
Sodium thiosulfate

Sodium thiosulfate , also spelled Sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Sodium2Sulfur2Oxygen3?5Hydrogen2Oxygen, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or ?hypo.?...
 is often referred to as hypo.

Thiosulfate is also a very aggressive species for the metal corrosion
Corrosion

Corrosion means the breaking down of essential properties in a material due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen....
. Steel and stainless steel are particularly sensitive to pitting corrosion
Pitting corrosion

Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the lack of oxygen around a small area....
 induced by thiosulfate. Addition of molybdenum
Molybdenum

Molybdenum , is a Group 6 element chemical element with the symbol Mo and atomic number 42. It has the List of elements by melting point melting point of any element....
 to stainless steel is needed to improve its resistance to pitting (AISI 316L hMo). Thiosulfates are also often produced by incomplete oxidation of sulfides (pyrite oxidation) or partial reduction of sulfate (Kraft paper
Kraft paper

Kraft paper is paper produced by the kraft process from wood pulp. It is strong and relatively coarse. Kraft paper is usually a brown colour but can be bleached to produce white paper....
).

The natural occurrence of the thiosulfate group is practically restricted to a very rare mineral
Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
 sidpietersite, Pb4(S2O3)O2(OH)2, as the presence of this anion in the mineral bazhenovite was recently disputed.