Potassium sulfite
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 384773163
| ImageFile = K2SO3.svg
| ImageSize = 150px
| IUPACName = Potassium sulfite
| OtherNames = {{Unbulleted list|E225}}
|Section1={{Chembox Identifiers
| CASNo = 10117-38-1
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|changed|FDA}}
| UNII = 015KZC652E
| PubChem = 24958
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| ChemSpiderID = 23332
| InChI = 1/2K.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2
| InChIKey = BHZRJJOHZFYXTO-NUQVWONBAU
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChI = 1S/2K.H2O3S/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2
| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
| StdInChIKey = BHZRJJOHZFYXTO-UHFFFAOYSA-L
| SMILES = [O-]S(=O)[O-].[K+].[K+]
}}
|Section2={{Chembox Properties
| Formula = K2SO3
| MolarMass = 158.26{{nbsp}}g/mol
| Appearance = White solid
| MeltingPt =
| BoilingPt =
| Solubility = Soluble
| pKa = 8
| MagSus = −64.0·10−6{{nbsp}}cm3/mol
}}
|Section7={{Chembox Hazards
| ExternalSDS =
| MainHazards =
| FlashPt = Non-flammable
}}
|Section8={{Chembox Related
| OtherAnions = Potassium sulfate
Potassium selenite
| OtherCations = Sodium sulfite
}}
}}
Potassium sulfite is the inorganic compound with the formula K2SO3. It is the salt of potassium cation and sulfite anion. It is a white solid that is highly soluble in water. Potassium sulfite is used for preserving food and beverages.{{Cite web | url = https://www.fao.org/gsfaonline/additives/details.html?id=229 | title = Potassium sulfite (225) | work = Codex Alimentarius | publisher = Food and Agriculture Organization of the United Nations }}
History
Potassium sulfite was first obtained by Georg Ernst Stahl in the early 18th century,{{Cite thesis |last=Coleby |first=L. J. M. |title=Studies in the chemical works of Stahl |date=1938 |degree=Doctoral |publisher=University of London |url=https://discovery.ucl.ac.uk/id/eprint/19500/ |pages=57–63, 181}} and was therefore known afterwards as Stahl's sulphureous salt. It became the first discovered sulfite and was first properly studied along with other sulfites by French chemists in the 1790s, and it was called sulphite of potash in the early 19th century.{{Cite book |last=Thomson |first=Thomas |url=https://books.google.com/books?id=m6P1HsMsAuYC&pg=PA2 |title=System of Chemistry |date=1807 |language=en}} Gilles-François Boulduc also discovered the salt in water of Passy in the 1720s.{{Cite journal |last=Chang |first=Ku-ming (Kevin) |date=2014 |title=Communications of Chemical Knowledge: Georg Ernst Stahl and the Chemists at the French Academy of Sciences in the First Half of the Eighteenth Century |url=https://www.jstor.org/stable/10.1086/678101 |journal=Osiris |volume=29 |issue=1 |pages=135–157 |doi=10.1086/678101 |jstor=10.1086/678101 |issn=0369-7827}}
Production and reactions
{{main|Sulfite#Reactions}}
{{see also|Wellman–Lord process}}
Potassium sulfite is produced by the thermal decomposition of potassium metabisulfite at 190 °C:{{cite book|doi=10.1002/9780470132333.ch49|isbn=9780470132333|chapter=Sulfites and Pyrosulfites of the Alkali Metals|year=1946|last1=Johnstone|first1=H. F.|title=Inorganic Syntheses |pages=162–167|volume=2}}
:{{chem2 | K2S2O5 -> K2SO3 + SO2 }}
Structure
The structure of solid {{chem2|K2SO3}}, as assessed by X-ray crystallography. The S-O distances are 1.515 Å, and the O-S-O angles are 105.2°{{cite journal |doi=10.3891/acta.chem.scand.40a-0479 |title=The Structure of Potassium Sulfite |date=1986 |last1=Andersen |first1=Leif |last2=Strömberg |first2=Dan |last3=Nevala |first3=H. |last4=Pohjola |first4=S. |last5=Niinistö |first5=Lauri |last6=Volden |first6=Hans V. |last7=Weidlein |first7=Johann |last8=Zingaro |first8=Ralph A. |journal=Acta Chemica Scandinavica |volume=40a |pages=479–480 |doi-access=free }}