Potassium sulfite

From Sciencemadness Wiki
Jump to: navigation, search
Potassium sulfite
IUPAC name
Potassium sulfite
Other names
Dipotassium sulfite
Potassium sulphite
Sulfurous acid, dipotassium salt
Molar mass 158.26 g/mol
Appearance White or slight yellowish solid
Density 2.35 g/cm3 (20 °C)[1]
Melting point 590 °C (1,094 °F; 863 K) (decomposes)
Boiling point Decomposes
Soluble with hydrolysis
Solubility Insoluble in chloroform, toluene
Acidity (pKa) 8
Safety data sheet Pfaltz & Bauer
Flash point Non-flammable
Related compounds
Related compounds
Sodium sulfite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Potassium sulfite is a chemical compound with the formula K2SO3, used as food preservative.



Potassium sulfite slowly oxidizes in air to potassium sulfate:

K2SO3 + ½ O2 → K2SO4


Potassium sulfite is a white or slight yellowish solid, soluble in water but insoluble in organic solvents.


Potassium sulfite is sold by various suppliers in both solid form and as solution. It can sometimes be found on eBay.


Potassium sulfite can be prepared by bubbling a predetermined volume of sulfur dioxide through an aqueous solution of potassium hydroxide. If an excess of sulfur dioxide is used, potassium bisulfite will form instead.

2 KOH + SO2 → K2SO3 + H2O

Gentle evaporation is required to eliminate the water from the solution, as strong heating can hydrolyze the sulfite or oxidize it to sulfate. Alternatively, one can cool the resulting solution and obtain sulfite crystals.


  • Reducing agent
  • Make (dry) sulfur dioxide generator
  • Make potassium sulfate
  • Make potassium bisulfite



Potassium sulfite releases sulfur dioxide in contact with a strong acid, which is irritant and toxic.


As it slowly oxidizes in open air, potassium sulfite should be stored in air tight containers or in a sulfur dioxide atmosphere, at temperatures between 0-30 °C.


Potassium bisulfite can be safely neutralized with bleach, hydrogen peroxide or simply left in open air to potassium sulfate which can be safely poured down the drain. However, it's not always necessary to neutralize it first.


  1. https://www.americanelements.com/potassium-sulfite-10117-38-1

Relevant Sciencemadness threads