Sodium sulfite

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Sodium sulfite
Image:Sodium sulfite.jpg
General
Systematic name	Sodium sulfite
Other names	hypo clear (photography)
Molecular formula	Na₂SO₃
SMILES	?
Molar mass	126.0418 g/mol
Appearance	white, granular
CAS number	[?-?-?]
Properties
Density and phase	2.633 g/cm³ (anhydrous) 1.561 g/cm³ (heptahydrate)
Solubility in water	67.8 g/100 ml of heptahydrate (18°C)
Solubility in glycerol	3 g/100 ml (?°C) (heptahydrate)
Melting point	251.8°C (525 K) (anhydrous) heptahydrate loses 7H₂O at 33.4°C
Boiling point	decomposes
Structure
Molecular shape	?
Coordination geometry	?
Crystal structure	hexagonal (anhydrous) monoclinic (heptahydrate)
Dipole moment	? D
Hazards
MSDS	External MSDS
Main hazards	?
NFPA 704
Flash point	?°C
R/S statement	R: ? S: ?
RTECS number	?
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other anions	?
Other cations	?
Related ?	?
Related compounds	SO₂ H₂SO₃ Na₂SO₄	?
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references

In chemistry, sodium sulfite is a soluble compound of sodium. Its chemical formula is Na₂S O₃. It has a molecular weight of 126.04. It is a product of S O₂ scrubbing, a part of the flue gas desulfurisation 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 halides to their respective acids, in photography and for reducing chlorine levels in pools.

1 Applications
2 Descriptive Chemistry
3 References
4 External links

[edit] Applications

It 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 textile industry as a bleaching, as a desulfurizing and as a dechlorinating agent and in leather trade for the sulfitization of tanning extracts. 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, include ore flotation, oil recovery, food preservatives, making dyes, and detergent. It forms a bisulfite adduct with aldehydes, and with ketones forms a sulfonic acid. It is used to purify or isolate aldehydes and ketones.

[edit] Descriptive Chemistry

Sodium sulfite is decomposed by even weak acids, giving up sulfur dioxide gas.

Na₂SO₃ + 2H⁺ → 2Na⁺ + H₂O + SO₂

A saturated aqueous solution has pH of ~9. Solutions exposed to air are eventually oxidized to sodium sulfate. If sodium sulfite is allowed to crystalize 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].