Sodium metabisulfite has the IUPAC name sodium pyrosulphite with chemical formula Na₂S₂O₅. Its EINECS registry number is 231-673-0 and CAS registry number is 7681-57-4. It is a white powder with a sulfur smell which is soluble in water. The substance is stable and incompatible with strong oxidizing agents, strong acids. It is easy to decompose affected with damp and gradually oxidized into sodium sulfate in the air.

Properties about Sodium metabisulfite: When it contacts with strong acids, it will release a poisonous gas (SO₂). When mixed with water, sodium metabisulfite will release sulfur dioxide (SO₂). On heating it by 65 °C releases sulfur dioxide, leaving sodium oxide behind. It is soluble with water and the aqueous solution is acidic.

Na₂S₂O₅ + 2 HCl → 2 NaCl + H₂O + 2 SO₂
Na₂S₂O₅ → Na₂O + 2 SO₂

Preparation of Sodium metabisulfite: Sodium metabisulfite can be prepared by absorption method using food grade soda solution to absorb SO₂ and then produce sodium pyrosulfite. At last, we will get food grade Sodium metabisulfite through impurity removing, filtration and drying.

Na₂CO₃ + 2 SO₂ + H₂O → 2 NaHSO₃ + CO₂
2 Na₂SO₃ → Na₂S₂O₅ + H₂O

You can also use the following method to prepared Sodium metabisulfite: First, you can add sulphur and 2 times compressed air into combustion furnace. There will be a spontaneous combustion at 600～800 °C. Second, the mixture should be cooled down accompany with impurity removing and water scrubbing and then is added into multistage reactor where will emerge reverse absorption with sodium carbonate at 45 °C. Finally, the flowing magma is centrifugalized and dried at 160 °C and then you will get the chemical substance.

O₂+S [Na₂CO₃→NaHSO₃[-H₂O]  → Na₂S₂O₅

Uses of Sodium metabisulfite: Sodium metabisulfite is used as a disinfectant, antioxidant and preservative agent and used as a preservative and antioxidant in food and is also known as E223. Sodium metabisulfite and potassium metabisulfite are the primary ingredients in campden tablets, used for wine and beer making. It is also commonly used in homebrewing and winemaking to sanitize equipment. The substance is used as a cleaning agent for potable water reverse osmosis membranes in desalination systems. It is also used to remove chloramine from drinking water after treatment. In addition, it is used in photography. Meanwhile, it can be used to remove tree stumps. It is also used as an excipient in some tablets, such as paracetamol.

When using Sodium metabisulfite, you must be cautious about it. The substance is harmful if swallowed and irritant to eyes, respiratory system and skin. When contact with acids, it will liberate toxic gas. There will be a risk of serious damage to eyes. In case of contact with eyes, you should rinse immediately with plenty of water and seek medical advice. When using it, you can wear suitable protective clothing. If swallowed, you must seek medical advice immediately and show this container or label.

You can still convert the following datas into molecular structure:(1)Canonical SMILES: [O-]S(=O)S(=O)(=O)[O-].[Na+].[Na+]
(2)InChI: InChI=1S/2Na.H2O5S2/c;;1-6(2)7(3,4)5/h;;(H,1,2)(H,3,4,5)/q2*+1;/p-2
(3)InChIKey: HRZFUMHJMZEROT-UHFFFAOYSA-L

Toxicity of Sodium metabisulfite: