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Sodium Thiosulfate pure LAB GRADE materials
Molecular Formula ::: Na2S2O3 - 5H2O
laboratory synthesis
In the laboratory, this salt can be prepared by heating an aqueous solution of sodium sulphite with sulphur.
Principal reactions and applications
Thiosulfate anion characteristically reacts with dilute acids to produce sulfur, sulfur dioxide and water-
1.Na2S2O3 + 2HCl →2NaCl + S + SO2 + H2O
This reaction is known as a "clock reaction", because when the sulfur reaches a certain concentration the solution turns from colourless to a pale yellow. This reaction has been employed to generate colloidal sulfur. When the protonation is conducted at low temperatures, 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 dissociation respectively.
Iodometry
In analytical chemistry, the most important use comes from the fact that the thiosulfate anion reacts stoichiometrically with iodine, reducing it to iodide as it is oxidized to tetrathionate:
Photographic processing
The terminal sulfur atom in S2O32− binds to soft metals with high affinity. Thus, silver halides, e.g. AgBr, typical components of photographic emulsions, dissolve upon treatment with aqueous thiosulfate:
2 S2O32− + AgBr →[Ag(S2O3)2]3−+ Br−
In this application to photographic processing, discovered by John Herschel and 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.
Gold extraction
Sodium thiosulfate is one component of an alternative lixiviant to cyanide for extraction of gold.[3] It forms a strong complex with gold(I) ions, [Au(S2O3)2]3−. The advantage of this approach is th
2 S2O32−(aq) + I2(aq) →S4O62−(aq) + 2 I−(aq)
Due to the quantitative nature of this reaction, as well as the fact that 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. 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.at thiosulfate is essentially non-toxic and 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)2]3− does not adsorb to activated carbon, which is the standard technique used in gold cyanidation to separate the gold complex from the ore slurry.
Process for DE CHLORINATION :::
Dissolve the 500 grams of Sodium Thiosulfate in a large pitcher of lukewarm tap water. Stir until all the crystals are dissolved. Then transfer the solution with a funnel to the gallon jug. Top off the jug to make a full gallon of stock solution.
Analytical chemistry
Sodium thiosulfate is also used in analytical chemistry. It can, when heated with a sample containing aluminum cation, produce a white precipitation:
2 Al3+ + 3 S2O32− + 3 H2O →3 SO2 + 3 S + 2 Al(OH)3
Medical
It is used as an antidote to cyanide poisoning. Thiosulfate acts as a sulfur donor for the conversion of cyanide to thiocyanate (which can then be safely excreted in the urine), catalyzed by the enzyme rhodanase.
It has also been used as treatment of calciphylaxis in hemodialysis patients with end-stage renal disease.[6]
It is used in the management of extravasations during chemotherapy. Sodium thiosulfate prevents alkylation and tissue destruction by providing a substrate for the alkylating agents that have invaded the subcutaneous tissues. The dose may be 2mL of 0.17M (a solution of 4mL 10% sodium thiosulfate and 6mL sterile water for injection). It may be instilled subcutaneously into multiple sites using a small gauge needle. There is limited data on this method with few recommendations.
in foot baths for prophylaxis of ringworm, and as a topical antifungal agent for tinea versicolor.
in measuring the volume of extracellular body fluid and the renal glomerular filtration rate.
Sodium thiosulfate is also used:
As a component in hand warmers and other chemical heating pads that produce heat by exothermic crystallization of a supercooled solution.
In bleach
In pH testing of bleach substances. The universal indicator and any other liquid pH indicators are destroyed by bleach, rendering them useless for testing the pH. If one first adds sodium thiosulfate to such solutions, it will neutralize the color-removing effects of bleach and allow 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
To dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers. The reduction reaction is analogous to the iodine reduction reaction. Treatment of tap water requires between 0.1 grams and 0.3 grams of pentahydrated (crystalline) sodium thiosulfate per 10 liters of water.
To lower chlorine levels in swimming pools and spas following super chlorination.
To remove iodine stains, e.g. after the explosion of nitrogen triiodide.
Similarly, sodium thiosulfate reacts with bromine to render harmless products. Solutions of sodium thiosulfate are commonly used as a precaution in chemistry laboratories when working with bromine.
In bacteriological water assessment.
In the tanning of leather.
To demonstrate the concept of reaction rate in chemistry classes. The thiosulfate ion can decompose into the sulfite ion and a colloidal suspension of sulfur, which is opaque. The equation for this acid-catalysed reaction is as follows:
S2O32−(aq) →SO32−(aq) + S(s)
To demonstrate the concept of supercooling in physics classes. Melted sodium thiosulfate is very easy to overcool to room temperature and when crystallization is forced, the sudden temperature jump to 48.3 °C can be experienced by touch.
As part of patina recipes for copper alloys.
Often used in pharmaceutical preparations as an anionic surfactant to aid in dispersion.
It can also be used as a very interesting solute in supersaturation experiments.
Sodium Thiosulfate solutions are almost exclusively used to standardize Iodine solutions or as back-titrants in titrations using Iodine. Solutions of Sodium Thiosulfate are most commonly standardized with Potassium Dichromate or Potassium Iodate solutions, which generate Iodine from Iodide. Starch indicator is typically used. The reaction with Iodine is:
Titrations with standard Sodium Thiosulfate solution are best conducted in the pH 5 - 9 range. Since this is not always possible, the titrations should be conducted rapidly and with adequate stirring to insure rapid reaction of the Thiosulfate, thus minimizing any acid-accelerated decomposition. This will also minimize the acid-catalyzed oxidation of Iodide (usually present in a titration involving Thiosulfate) to Iodate, which could lead to decreased accuracy.
Sodium Thiosulfate solutions are subject to bacterial decomposition and chemical deterioration. Sodium Thiosulfate solutions decompose in acid solution resulting in the evolution of Sulfur Dioxide gas and precipitation of elemental Sulfur. Contact with Carbon Dioxide in the air can produce the acidity leading to this decomposition, which is faster in more dilute Thiosulfate solutions.
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