Sodium metabisulfite, with the chemical formula Na2S2O5, is a white to yellowish crystalline powder with a sulfurous odor. It is soluble in water and commonly used in various industries due to its properties as a reducing agent, antioxidant, and preservative. Here is some detailed information about sodium metabisulfite:

1. **Chemical Properties**: Sodium metabisulfite is a sodium salt of metabisulfurous acid. It is a stable compound, but it releases sulfur dioxide gas upon contact with acids. It is commonly used in its anhydrous form but can also be found as a pentahydrate.

2. **Industrial Uses**:
– **Food Industry**: Sodium metabisulfite is widely used in the food industry as a preservative to extend the shelf life of various food products. It is also used as an antioxidant to prevent browning and oxidation in foods.
– **Water Treatment**: It is used in water treatment processes to remove chlorine and chloramine from water. It also acts as a disinfectant and dechlorinating agent.
– **Textile Industry**: Sodium metabisulfite is used as a reducing agent in dyeing processes in the textile industry to remove excess dyes and improve color fastness.
– **Pulp and Paper Industry**: It is used as a bleaching agent in the pulp and paper industry to brighten paper pulp and improve paper quality.
– **Photography**: In photography, it is used in developing and fixing processes as a reducing agent to stabilize the image.
– **Leather Industry**: Sodium metabisulfite is used as a reducing agent in tanning processes to remove impurities from leather.
– **Chemical Industry**: It finds applications as a reducing agent, antioxidant, and sulfur source in various chemical processes.

3. **Health and Safety**:
– Sodium metabisulfite can cause skin and eye irritation upon contact. It may also trigger allergic reactions in sensitive individuals.
– Ingestion or inhalation of sodium metabisulfite can cause adverse health effects, especially in high concentrations. It is important to handle it with care and follow safety guidelines.

4. **Regulatory Status**:
– The use of sodium metabisulfite is regulated in various industries to ensure its safe and appropriate use. Maximum allowable limits are set for its use in food products.

5. **Storage**: Sodium metabisulfite should be stored in a cool, dry place away from incompatible materials. It should be kept in a well-sealed container to prevent moisture absorption.

Overall, sodium metabisulfite is a valuable compound with diverse industrial applications, primarily due to its reducing and preserving properties. It plays a crucial role in various industries, including food, water treatment, textiles, and photography.