Sodium sulfite

Structural formula
General
Surname	Sodium sulfite
other names	Sodium sulphate E  221
Molecular formula	Na 2 SO 3
Brief description	white, crystalline, odorless powder
External identifiers / databases
CAS number 7757-83-7 EC number 231-821-4 ECHA InfoCard 100,028,929 PubChem 24437 Wikidata Q407806
properties
Molar mass	126.04 g mol −1
Physical state	firmly
density	2.63 g cm −3 1.539 g cm −3 (heptahydrate)
Melting point	Decomposition from 500  ° C
solubility	Easily soluble in water (220 g l −1 at 20 ° C)
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
Toxicological data	3560 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Sodium sulfite Na ₂ SO ₃ (not to be confused with sodium sulfide Na ₂ S) is the sodium salt of sulphurous acid .

Extraction and presentation

Sodium sulphite is formed when sulfur dioxide is introduced into sodium hydroxide solution

${\displaystyle {\ce {2 NaOH + SO2 -> Na2SO3 + H2O}}}$

or by neutralizing caustic soda with sulphurous acid.

Sodium sulfite can also be obtained by reacting a sodium hydrogen sulfite solution with sodium hydroxide solution or a sodium carbonate solution and is also formed as a by-product in the production of naphthols and / or phenols from naphthalene and benzenesulfonic acids .

properties

Sodium sulfite is a white to slightly yellowish, odorless, crystalline powder. It crystallizes out as a heptahydrate from aqueous solution . It is hygroscopic and can be prepared by oxygen to sodium sulfate (Na ₂ SO ₄ ) is oxidized to be. With acids it decomposes with the formation of sulfur dioxide. The heptahydrate splits off water of crystallization from 150 ° C. The water-free form is more stable to oxidation than the heptahydrate. Sodium sulfite is easily soluble in water, the solution has an alkaline reaction and has a reducing effect (for example, potassium permanganate solution is discolored). It has a germicidal effect.

The compound has a trigonal crystal structure with the space group P 3 (space group no. 147) .

use

• Sodium sulfite serves as a preservative and antioxidant for food (additive number E221). As part of the so-called dumpling aid , it prevents potato dough from turning brown (oxidizing). In the photo industry , sodium sulfite anhydrous photo grade is used as an anti-oxidant for developer solutions. In the chemical and chemical-technical industry, sodium thiosulfate ( fixing salt ) is produced from sodium sulfite with the addition of sulfur . In the chemical fiber and textile industries it is used as a bleaching agent and to destroy active chlorine . It is also an aid in water treatment, because it acts as a corrosion protection by removing oxygen and is used to remove chlorine from service water. In the rubber and pulp industry , it helps to improve the quality of products. It is also an intermediate in the production of sodium dithionite .
• It is offered as an active ingredient against the formation of germs or algae.
• It is an antidote for nicotine poisoning .
• In addition to sodium dithionite, it is used as an active ingredient in the ink killer and is a component of stain removers .

Individual evidence

1. ↑ Entry on E 221: Sodium sulphite in the European database for food additives, accessed on June 27, 2020.
2. ↑ ^{a b c d e f g h i j} record with sodium sulfite in the GESTIS database of IFA , retrieved on July 13, 2018(JavaScript required) .
3. ↑ ^{a b c d} Entry on sodium sulfite. In: Römpp Online . Georg Thieme Verlag, accessed on July 13, 2018.