Sodium sulfite

Sodium sulfite

anhydrous hydrate
Names
IUPAC name Sodium sulfite
Other names Hypo clear (photography) E221
Identifiers
CAS Number	7757-83-7 Y
3D model (JSmol)	Interactive image
ChemSpider	22845 Y
ECHA InfoCard	100.028.929
E number	E221 (preservatives)
PubChem CID	24437
RTECS number	WE2150000
UNII	VTK01UQK3G Y
CompTox Dashboard (EPA)	DTXSID2044260
InChI InChI=1S/2Na.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2 Y Key: GEHJYWRUCIMESM-UHFFFAOYSA-L Y InChI=1/2Na.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2 Key: GEHJYWRUCIMESM-NUQVWONBAK
SMILES [O-]S(=O)[O-].[Na+].[Na+]
Properties
Chemical 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) 500 °C (anhydrous)
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
NFPA 704 (fire diamond)	2 0 0
Flash point	Non-flammable
Related compounds
Other anions	Sodium selenite
Other cations	Potassium sulfite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Sodium sulfite (sodium sulphite) is a soluble sodium salt of sulfurous acid with the chemical formula Na₂SO₃. 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.

Preparation

Sodium sulfite can be prepared in lab by reacting sodium carbonate with sulfurous acid:

Na₂CO₃ + H₂SO₃ → Na₂SO₃ + CO₂ + H₂O

The second way of prepare it in lab is reacting sodium hydroxide solution with sulfur dioxide gas:

2 NaOH + SO₂ → Na₂SO₃ + H₂O

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:

Na₂SO₃ + 2 HCl → 2 NaCl + SO₂ + H₂O

Applications

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.

It was revealed that sodium sulfite, the aqueous ion of sulfur dioxide, contain pro-inflammatory properties in vitro and induce potent chemotactic factor IL-8 production. Mech-anistic studies consider that this material could possibly act through signal transduction pathways NF-κ B, ERK, and p-38-dependent pathways.

Another important property of sodium sulfite is the fact that compound can inhibit Candida albicans growth in RPMI1640 medium. Some new experiments indicate that it can induce cel-lular activation, resulting in degranulation in mast cells through a non-IgE-depent pathway. These properties of sodium sulfite demonstrate new features of the substance and prospect for further growth its consumption in the world.

Reactions

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.

Descriptive chemistry

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

Na₂SO₃ + 2 H⁺ → 2 Na⁺ + 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 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.