Sodium thiosulfate
Encyclopedia : S : SO : SOD : Sodium thiosulfate
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| General | |
| Systematic name | Sodium thiosulfate (Sodium thiosulphate) |
| Other names | Sodium hyposulfite Hyposulfate of soda |
| Molecular formula | Na2S2O3 |
| Molar mass | 158.09774 g/mol |
| Appearance | White crystals |
| CAS number | [7772-98-7] |
| Properties | |
| Density and phase | 1.667 g/cm3 |
| Solubility in water | Very Soluble |
| Melting point | 48.3 °C |
| Boiling point | N/A |
| Basicity (pKb) | N/A |
| Structure | |
| Coordination geometry | tetrahedral anion |
| Crystal structure | ? |
| Dipole moment | ? D |
| Hazards | |
| MSDS | External MSDS |
| EU classification | Non-toxic. |
| R-phrases | R35 |
| S-phrases | S1/2, S26, S37/39, S45 |
| NFPA 704 | |
| Flash point | Non flammable |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) [Chemical infoboxInfobox disclaimer and references] | |
Sodium thiosulfate (Na2S2O3) is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3•5H2O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo.”
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 sulfur bears significant negative charge and the S-O interactions have more double bond character. The first protonation of thiosulfate occurs at sulfur.
Contents
Production and chemical synthesisHolleman, A. F.; Wiberg, E. \"Inorganic Chemistry\" Academic Press: San Diego, 2001.
Sodium thiosulfate is produced chiefly from liquid waste products of sodium sulfide or sulfur dye manufacture. It is also arises from the action of sodium sulfite on sulfur in aqueous solution. As such, the anion S2O32− represents a water-soluble form of elemental sulfur.Principal reactions and applicationsHolleman, A. F.; Wiberg, E. \"Inorganic Chemistry\" Academic Press: San Diego, 2001.
Thiosulfate anion characteristically reacts with dilute acids to produce sulfur, sulfur dioxide and water:
- S2O32−(aq) + 2H+ (aq) → S(s) + SO2(g) + H2O(l)
This reaction has been employed to general colloidal sulfur. When the protonation is conducted at low temperatures, H2S2O3 can be obtained. It is a strong acid pKa = 0.6, 1.7.
Iodometry
Perhaps most notably in the laboratory, the thiosulfate anion reacts stoichiometrically with iodine, reducing it to iodide as it is oxidized to tetrathionate:
- 2S2O32−(aq) + I2(aq) → S4O62−(aq) + 2I−(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. Photography
The "planetary" sulfur atom in S2O32- binds to "soft" metals with high affinity. Thus it dissolves silver halides, e.g. AgBr, which is a component of photographic emulsions:
- 2 S2O32- + AgBr → [Ag(S2O3)2]3-) + Br-
In this application, discovered by John Herschel, sodium thiosulfate is known as a fixer and is used for both film and paper. It is also used in the tanning of leather, in chemical manufacture, in bacteriological water assessment, and in treating cyanide poisoning. Other uses
- This substance is also being used for automatic hand warmers. It is also used in photography as a fixing agent.
- Sodium thiosulfate can also be used in pH testing of bleach substances. The universal indicator and any other liquid pH indicator 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 dithionate.
- Sodium thiosulfate can be used to dechlorinate tap water for aquariums or treat effluents 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 (crystaline) sodium thiosulfate per 10 liters of water.
- It is used to lower chlorine levels in swimming pools and spas following super chlorination.
- It can also be used to remove iodine stains, e.g. after the explosion of nitrogen triiodide.
References
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.
- S2O32−(aq) + 2H+ (aq) → S(s) + SO2(g) + H2O(l)
Iodometry
Perhaps most notably in the laboratory, the thiosulfate anion reacts stoichiometrically with iodine, reducing it to iodide as it is oxidized to tetrathionate:- 2S2O32−(aq) + I2(aq) → S4O62−(aq) + 2I−(aq)
Photography
The "planetary" sulfur atom in S2O32- binds to "soft" metals with high affinity. Thus it dissolves silver halides, e.g. AgBr, which is a component of photographic emulsions:- 2 S2O32- + AgBr → [Ag(S2O3)2]3-) + Br-
Other uses
- This substance is also being used for automatic hand warmers. It is also used in photography as a fixing agent.
- Sodium thiosulfate can also be used in pH testing of bleach substances. The universal indicator and any other liquid pH indicator 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 dithionate.
- Sodium thiosulfate can be used to dechlorinate tap water for aquariums or treat effluents 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 (crystaline) sodium thiosulfate per 10 liters of water.
- It is used to lower chlorine levels in swimming pools and spas following super chlorination.
- It can also be used to remove iodine stains, e.g. after the explosion of nitrogen triiodide.
References
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.