| IUPAC name
Sodium hydrogen sulfite
| Other names
|Molar mass||104.061 g/mol|
|Appearance||White or white-yellowish crystalline solid|
|Odor||Slight sulfurous odor|
|Density||1.48 g/cm3 (at 20 °C)|
|Melting point||150 °C (302 °F; 423 K) (decomposition begins at 104 °C)|
|Boiling point||315 °C (599 °F; 588 K) (decomposes)|
|42 g/100 mL|
|Safety data sheet||FisherScientific|
|Lethal dose or concentration (LD, LC):|
LD50 (Median dose)
|2340 mg/kg (oral, rat)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Sodium bisulfite or sodium hydrogen sulfite is an air sensitive chemical compound with the formula NaHSO3, mostly used as food additive (E222).
Sodium bisulfite will slowly oxidize in air to sodium bisulfate:
- NaHSO3 + ½ O2 → NaHSO4
Small quantities of sulfur dioxide and water are released during the reaction, with sodium sulfate also forming.
Sodium bisulfite is a white or white-yellowish solid, with a slight sulfurous odor and a disagreeable taste. It is soluble in water. It melts at 150°C, and decomposes at 315 °C, with first signs of decomposition appearing around 100-104 °C.
Sodium bisulfite can be purchased online. Some winemaking suppliers may have it in their stock.
Sodium bisulfite can be prepared by bubbling excess sulfur dioxide through a solution of sodium carbonate or sodium hydroxide. Make sure no air is present in the sulfur dioxide stream, as it will oxidize the bisulfite to bisulfate. Since heat decomposes the bisulfate, the water can only be removed via vacuum. Do this until you see sodium bisulfite starting to precipitate/crystallize out of the solution. The solution is further cooled in a low oxygen medium to extract as much compound from the solution as possible. The resulting crystals are vacuum filtered and washed with cold water or ethanol. The wet solid is dried in a vacuum desiccator.
Sodium bisulfite is irritant.
Sodium bisulfite should be stored in air-tight bottles, as it will slowly oxidize in open air. Aqueous solutions rapidly oxidize in air.