Sodium sulfite

Sodium sulfite
Sodium sulfite


CAS number 7757-83-7 YesY
PubChem 24437
ChemSpider 22845 YesY
RTECS number WE2150000
Jmol-3D images Image 1
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)
500 °C (anhydrous)

Boiling point


Solubility in water 678 g/L (18 °C, heptahydrate)
Crystal structure hexagonal (anhydrous)
monoclinic (heptahydrate)
EU Index Not listed
NFPA 704
NFPA 704.svg
Flash point Non-flammable
Related compounds
Other anions Sodium selenite
Other cations Potassium sulfite
Related compounds Sodium bisulfite
Sodium metabisulfite
Sodium sulfate
 YesY sulfite (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.



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


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.

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.[1]


  1. ^ Merck Index of Chemicals and Drugs, 9th ed. monograph 8451

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Look at other dictionaries:

  • sodium sulfite — natrio sulfitas statusas T sritis chemija formulė Na₂SO₃ atitikmenys: angl. sodium sulfite; sulfite rus. натрий сернистокислый; натрия сульфит; сульфит ryšiai: sinonimas – dinatrio trioksosulfatas …   Chemijos terminų aiškinamasis žodynas

  • sodium sulfite — noun : a sulfite of sodium: as a. : the crystalline normal salt Na2SO3 used chiefly as a reducing agent, bleaching agent, and antichlor, in photographic developing and fixing baths, and in preserving foods b. : sodium bisulfite a c …   Useful english dictionary

  • sodium sulfite — noun the sodium salt of sulfurous acid, NaSO, used as a food preservative, in photography and in many industrial applications …   Wiktionary

  • sodium sulfite — Chem. a white, crystalline, water soluble solid, Na2SO3, used chiefly as a food preservative, as a bleaching agent, and as a developer in photography. * * * …   Universalium

  • sodium sulfite — Na2SO3, fairly stable in the anhydrous form; used as a reagent and as a preservative and antioxidant …   Medical dictionary

  • sodium sulfite — A chemical used in photography, paper making, water treatment, and for other purposes …   English dictionary of cancer terms

  • Sulfite de sodium — Structure du sulfite de sodium Général Nom IUPAC sulfite de disodium …   Wikipédia en Français

  • Sodium bisulfite — Sodium bisulfite …   Wikipedia

  • Sodium thiosulfate — Sodium thiosulfate …   Wikipedia

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