The oxidation reaction process and Chemical equation of sodium metabisulfite are as follows:

Firstly, sodium metabisulfite absorbs water: Na2S2O5+H2O==2NaHSO3, and sodium bisulfite oxidizes: 2NaHSO3+O2==2NaHSO4. The oxidized sodium bisulfite can also react with unabsorbed sodium metabisulfite or sodium bisulfite: 2NaHSO4+Na2S2O5=2Na2SO4+2SO2+H2ONaHSO3+NaHSO4==Na2SO4+SO2+H2O, and sodium metabisulfite itself can slowly decompose:

Na2S2O5==Na2SO3+SO2

Sodium metabisulfite (Na2S2O5) is a inorganic compound, which is white crystal with irritating smell. It is soluble in water, and the aqueous solution is acidic. Contact with strong acid will release sulfur dioxide and generate corresponding salts. If left in the air for a long time, it will oxidize to sodium sulfate, so sodium metabisulfite can’t be stored for too long time.

Sodium Metabisulfite Oxidation