Sodium metabisulfite

Sodium metabisulfite (or sodium metabisulphite) is an inorganic compound of chemical formula Na2S2O5. It is a white crystalline or powder solid with a slight sulfur odor. Sodium metabisulfite is used as a disinfectant, antioxidant, and preservative agent.

Chemical Properties

Sodium metabisulfite is composed of sodium ions (Na+) and metabisulfite ions (S2O5^2-). It is a salt of sulfurous acid (H2SO3), containing two sulfite (SO3^2-) ions linked by a single bond. The sulfur atoms are in a state of oxidation of +4. Sodium metabisulfite can be prepared by evaporating a solution of sodium bisulfite (NaHSO3) saturated with sulfur dioxide (SO2).

Uses

Sodium metabisulfite has several key uses in different industries.

Food Industry

In the food industry, it is commonly used as a preservative and antioxidant. It helps to prevent the browning of fruits and vegetables, and it extends the shelf life of baked goods. It is also used in wine and beer making, as it kills bacteria and wild yeast. This use falls under the E number food additives classification E223.

Photography

In photography, sodium metabisulfite is used as a photographic fixer. It acts as an antioxidant, which protects the developing photo from oxidation, thus preserving the image.

Water Treatment

In water treatment, it is used to remove excess chlorine. Sodium metabisulfite reacts with chlorine to form harmless products, thus making the water safe for aquatic life.

Other Uses

Other uses include its role in the leather industry for the bating process, in the paper and pulp industry as a bleaching agent, and in the textile industry for dyeing and cotton printing.

Health Effects

Exposure to sodium metabisulfite can cause a range of health effects. These can include skin and eye irritation, respiratory problems, and in severe cases, anaphylactic shock. People with asthma or allergies to sulfites are particularly at risk.

See Also

• Sodium bisulfite
• Sulfurous acid
• Sulfur dioxide
• E number