Although sodium metabisulfite and sodium hyposulfite have similar names, they differ significantly in chemical properties, uses, and safety.
1. Basic Information
Sodium metabisulfite, also known as sodium metabisulfite, has the molecular formula Na₂S₂O₅. It is usually a white or yellow crystalline powder with a strong sulfur dioxide odor. Sodium hyposulfite, commonly known as sodium hydrosulfite, has the molecular formula Na₂S₂O₄ and appears as white granular crystals or a pale yellow powder.
2. Chemical Properties
Sodium metabisulfite is readily soluble in water, and its aqueous solution is acidic. With prolonged storage, it gradually oxidizes to sodium sulfate. Sodium hyposulfite, on the other hand, has strong reducing properties and is easily oxidized in air. It may generate heat or even ignite when exposed to water or moisture, and it can also react with various metal ions.
3. Uses
Sodium metabisulfite is widely used as a food additive, providing bleaching, preservation, and antioxidant functions. In the dyeing and printing industry, it is used as a dechlorinating agent after bleaching cotton fabrics. Sodium hyposulfite is an important reducing agent in the dyeing and printing industry and can be used for preservation in the food industry, but its use and dosage are strictly limited.
4. Safety
Sodium metabisulfite is somewhat irritating to the skin, eyes, and respiratory tract, but is relatively safe within the prescribed usage range. Sodium hyposulfite is classified as a Class 1 flammable substance in contact with water; it may release a large amount of heat and sulfur dioxide upon contact with water, posing a risk of combustion and explosion, and is highly irritating and corrosive to humans.
