| Sodium sulfite | |
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anhydrous
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hydrate
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Sodium sulfite |
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Other names
Hypo clear (photography) |
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| Identifiers | |
| CAS number | 7757-83-7 |
| PubChem | 24437 |
| ChemSpider | 22845 |
| UNII | VTK01UQK3G |
| RTECS number | WE2150000 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | Na2SO3 |
| Molar mass | 126.043 g/mol |
| Appearance | white solid |
| Density | 2.633 g/cm3 (anhydrous) 1.561 g/cm3 (heptahydrate) |
| Melting point |
33.4 °C (dehydration of heptahydrate) |
| Boiling point |
Decomposes(separate (substances) into constituent elements) |
| Solubility in water | 678 g/L (18 °C, heptahydrate) |
| Structure | |
| Crystal structure | hexagonal (anhydrous) monoclinic (heptahydrate) |
| Hazards | |
| MSDS | ICSC 1200 |
| EU Index | Not listed |
| NFPA 704 |
0
2
0
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| Flash point | Non-flammable |
| Related compounds | |
| Other anions | Sodium selenite |
| Other cations | Potassium sulfite |
| Related compounds | Sodium bisulfite Sodium metabisulfite Sodium sulfate |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Sodium sulfite (sodium sulphite) is a soluble sodium salt of sulfurous acid. It is a product of sulfur dioxide scrubbing, a part of the flue-gas desulfurization process. It is also used as a preservative to prevent dried fruit from discoloring, and for preserving meats, and is used in the same way as sodium thiosulfate to convert elemental halogens to their respective hydrohalic acids, in photography and for reducing chlorine levels in pools.
Contents |
Sodium sulfite can be prepared in lab by reacting sodium carbonate with sulfurous acid:
The second way of prepare it in lab is reacting sodium hydroxide solution with sulfur dioxide gas:
By adding few drops of concentrated hydrochloric acid it can be tested that sodium sulfite is formed or not. if the solution of Na2SO3 gives bubbles of sulfur dioxide gas with HCl, that means the solution of sodium hydroxide is turned to sodium sulfite:
Sodium sulfite is primarily used in the pulp and paper industry. It is used in water treatment as an oxygen scavenger agent, in the photographic industry to protect developer solutions from oxidation and (as hypo clear solution) to wash fixer (sodium thiosulfate) from film and photo-paper emulsions, in the textile industry as a bleaching, desulfurizing and dechlorinating agent and in the leather trade for the sulfitization of tanning extracts. It is used in the purification of TNT for military use. It is used in chemical manufacturing as a sulfonation and sulfomethylation agent. It is used in the production of sodium thiosulfate. It is used in other applications, including froth flotation of ores, oil recovery, food preservatives, making dyes.
Sodium sulfite forms a bisulfite adduct with aldehydes, and with ketones forms a sulfonic acid. It is used to purify or isolate aldehydes and ketones.
Sodium sulfite is decomposed by even weak acids, giving up sulfur dioxide gas.
A saturated aqueous solution has pH of ~9. Solutions exposed to air are eventually oxidized to sodium sulfate. If sodium sulfite is allowed to crystallize from aqueous solution at room temperature or below, it does so as a heptahydrate. The heptahydrate crystals effloresce in warm dry air. Heptahydrate crystals also oxidize in air to form the sulfate. The anhydrous form is much more stable against oxidation by air.[1]