Quick Search

PRODUCTS

SODIUM THIOSULFATE

SODIUM THIOSULFATE

CAS NO : 7772-98-7

SYNONYMS: Sodium thiosulphate; Disodium thiosulfate; sodiumthiosulfate; Chlorine Cure; Chlorine Control; Sodium thiosulphate (Na2S2O3); Thiosulfuric acid, disodium salt; disodium sulfurothioate; Na2S2O3; Thiosulfuric acid (H2S2O3), disodium salt; sodium sulfothioate; Sodium thiosulfate, 0.1 N standard solution; Sodium thiosulfate, 98.5%, extra pure, anhydrous; Sodium thiosulfate, 99%, for analysis, anhydrous; Sodium thiosulfate, anhydrous; Sodium thiosulfate concentrate; sodium thiosulfat; sodium thiosulphate; sodium thio-sulfate; Sodium oxide sulfide; Hypo alcohol, in ethanol; Na2O3S2; anhydrous sodium thiosulfate; Sodium thiosulfate,anhydrous; Thiosulfuric acid (H2S2O3), sodium salt (1:2); sodium thiosulfate (anhydrous); Sodium thiosulfate solution, 1 M; Sodium thiosulfate, AR, >=98%; Sodium thiosulfate, LR, >=97%; Sodothiol; Sulfactol; Sulfothiorine; Sodium thiosulfate solution, 0.1 M; Sodium thiosulfate, p.a., 98.0%; Sodium thiosulfate solution, 0.01 M; Sodium thiosulfate solution, 0.025 M; Sodium thiosulfate, 99%; Sodium Thiosulfate, 0.1N Volumetric Solution; Sodium thiosulfate, SAJ first grade, >=90.0%; Sodium thiosulfate, >=99.99% trace metals basis; Sodium thiosulfate, Vetec(TM) reagent grade, 99%; Sodium thiosulfate solution, 2 g/dL in deionized water; Sodium thiosulfate, anhydrous, Trace metals grade 99.99%; Sodium thiosulfate, purum p.a., anhydrous, >=98.0% (RT); Sodium thiosulfate, anhydrous, >=98% (calc. to the dried substance); Sodium thiosulfate 2.5M solution (+/- 0.1M) pH 7.0 - 9.0 (Sodium carbonate added as a preservative); Sodium thiosulfate solution, Silver stain kit component, 0.5 % (w/v) sodium thiosulfate in H2O

Chemical formula    Na2S2O3


Molar mass    158.11 g/mol (anhydrous)

248.18 g/mol (pentahydrate)

Appearance    White crystals

Odor    Odorless

Density    1.667 g/cm3

Melting point    48.3 °C (118.9 °F; 321.4 K) (pentahydrate)

Boiling point    100 °C (212 °F; 373 K) (pentahydrate, - 5H2O decomposition)

Solubility in water    70.1 g/100 mL (20 °C)

231 g/100 mL (100 °C)

Solubility    negligible in alcohol

Refractive index (nD)    1.489

Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula Na2S2O3.xH2O. 

Typically it is available as the white or colorless pentahydrate, Na2S2O3·5H2O.

The solid is an efflorescent (loses water readily) crystalline substance that dissolves well in water.

Sodium thiosulfate is used in gold mining, water treatment, analytical chemistry, the development of silver-based photographic film and prints, and medicine. 

The medical uses of sodium thiosulfate include treatment of cyanide poisoning and pityriasis.

 It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system.

Molecular Weight    158.11 g/mol    

Hydrogen Bond Donor Count    0    

Hydrogen Bond Acceptor Count    4    

Rotatable Bond Count    0    

Exact Mass    157.908425 g/mol    

Monoisotopic Mass    157.908425 g/mol    

Topological Polar Surface Area    104 Ų    

Heavy Atom Count    7    

Formal Charge    0    

Complexity    82.6    

Isotope Atom Count    0

Defined Atom Stereocenter Count    0    

Undefined Atom Stereocenter Count    0    

Defined Bond Stereocenter Count    0

Undefined Bond Stereocenter Count    0    

Covalently-Bonded Unit Count    3    

Compound Is Canonicalized    Yes

Medical uses

Main article: Sodium thSodium thiosulfate is used in the treatment of cyanide poisoning.iosulfate (medical use)

Other uses include topical treatment of ringworm and tinea versicolor, and treating some side effects of hemodialysis and chemotherapy.

Iodometry
In analytical chemistry, the most important use comes because the thiosulfate anion reacts stoichiometrically with iodine in aqueous solution, reducing it to iodide as the thiosulfate is oxidized to tetrathionate:

2 S2O2−3 + I2 → S4O2−6 + 2 I−
Due to the quantitative nature of this reaction, as well as because Na2S2O3·5H2O has an excellent shelf-life, it is used as a titrant in iodometry. 

Na2S2O3·5H2O is also a component of iodine clock experiments.

This particular use can be set up to measure the oxygen content of water through a long series of reactions in the Winkler test for dissolved oxygen.

 It is also used in estimating volumetrically the concentrations of certain compounds in solution (hydrogen peroxide, for instance) and in estimating the chlorine content in commercial bleaching powder and water.

Photographic processing

Silver halides, e.g., AgBr, typical components of photographic emulsions, dissolve upon treatment with aqueous thiosulfate:

This application as a photographic fixer was discovered by John Herschel. It is used for both film and photographic paper processing; the sodium thiosulfate is known as a photographic fixer, and is often referred to as 'hypo', from the original chemical name, hyposulphite of soda. Ammonium thiosulfate is typically preferred to sodium thiosulfate for this application.

Gold extraction

Sodium thiosulfate and ammonium thiosulfate are a component of an alternative lixiviants to cyanide for extraction of gold.

Thiosulfate forms strong soluble complexes with gold(I) ions, [Au(S2O3)2]3−. The advantages of this approach are that (i) thiosulfate is essentially nontoxic and (ii) that ore types that are refractory to gold cyanidation (e.g. carbonaceous or Carlin-type ores) can be leached by thiosulfate. Some problems with this alternative process include the high consumption of thiosulfate, and the lack of a suitable recovery technique, since [Au(S2O3) does not adsorb to activated carbon, which is the standard technique used in gold cyanidation to separate the gold complex from the ore slurry.

Neutralizing chlorinated water

It is used to dechlorinate tap water including lowering chlorine levels for use in aquariums, swimming pools, and spas (e.g., following superchlorination) and within water treatment plants to treat settled backwash water prior to release into rivers. The reduction reaction is analogous to the iodine reduction reaction.

In pH testing of bleach substances, sodium thiosulfate neutralizes the color-removing effects of bleach and allows one to test the pH of bleach solutions with liquid indicators. The relevant reaction is akin to the iodine reaction: thiosulfate reduces the hypochlorite (active ingredient in bleach) and in so doing becomes oxidized to sulfate. The complete reaction is:

4 NaClO + Na2S2O3 + 2 NaOH → 4 NaCl + 2 Na2SO4 + H2O

Similarly, sodium thiosulfate reacts with bromine, removing the free bromine from solution. 

Solutions of sodium thiosulfate are commonly used as a precaution in chemistry laboratories when working with bromine and for the safe disposal of bromine, iodine, or other strong oxidizers.

Structure

Two polymorphs are known of the pentahydrate. The anhydrous salt exists in several polymorphs.

 In the solid state, the thiosulfate anion is tetrahedral in shape and is notionally derived by replacing one of the oxygen atoms by a sulfur atom in a sulfate anion. 

The S-S distance indicates a single bond, implying that the terminal sulfur holds a significant negative charge and the S-O interactions have more double-bond character.

Production

On an industrial scale, sodium thiosulfate is produced chiefly from liquid waste products of sodium sulfide or sulfur dye manufacture.

In the laboratory, this salt can be prepared by heating an aqueous solution of sodium sulfite with sulfur or by boiling aqueous sodium hydroxide and sulfur according to this equation

6 NaOH + 4 S → 2 Na2S + Na2S2O3 + 3 H2O

Principal reactions

Upon heating to 300 °C, it decomposes to sodium sulfate and sodium polysulfide:

4 Na2S2O3 → 3 Na2SO4 + Na2S5

Thiosulfate salts characteristically decompose upon treatment with acids. Initial protonation occurs at sulfur. 

When the protonation is conducted in diethyl ether at −78 °C, H2S2O3 (thiosulfuric acid) can be obtained.

 It is a somewhat strong acid with pKas of 0.6 and 1.7 for the first and second dissociations, respectively.

Under normal conditions, acidification of solutions of this salt excess with even dilute acids results in complete decomposition to sulfur, sulfur dioxide, and water:

Na2S2O3 + 2 HCl → 2 NaCl + S + SO2 + H2O

This reaction is known as a "clock reaction", because when the sulfur reaches a certain concentration, the solution turns from colorless to a pale yellow. 

This reaction has been employed to generate colloidal sulfur. 

This process is used to demonstrate the concept of reaction rate in chemistry classes.

  • Share !
E-NEWSLETTER