What is Sodium Metabisulfite CAS 7681-57-4?

Sodium metabisulfite, also called sodium pyrosulfite or disodium metabisulfite, is an inorganic sulfite salt with the formula Na2S2O5. It is supplied as a white to slightly yellow crystalline powder and acts as a reducing agent, antioxidant, preservative and dechlorination agent.

What happens when Sodium Metabisulfite dissolves in water?

It dissolves to form bisulfite and sulfite species and can release sulfur dioxide, especially in acidic solution. The resulting solution is reducing and has antimicrobial activity, so dosing should be controlled to avoid excess sulfite or sulfur dioxide.

Is Sodium Metabisulfite available as food grade?

The listing covers industrial and food grades. Food-grade sodium metabisulfite is used as a permitted preservative and antioxidant where regulations allow, often associated with E223, but sulfite sensitivity, labeling and destination-market limits must be considered.

What are the main industrial applications of CAS 7681-57-4?

Typical uses include water and wastewater dechlorination, textile bleaching and antichlor treatment, pulp and paper, leather processing, photography, gold recovery or cyanide treatment, and other chemical reduction processes.

Which specifications should I check before ordering Sodium Metabisulfite?

Confirm the grade, Na2S2O5 purity, SO2 content, pH, iron, heavy metals, arsenic and water-insoluble matter. Food-grade material should also meet the preservative purity limits and regulatory requirements of the destination market.

Sodium Metabisulfite CAS 7681-57-4

Sodium Metabisulfite (Na₂S₂O₅), CAS 7681-57-4, is an inorganic sulfite supplied in industrial and food grades as a reducing agent, dechlorination agent, antioxidant and preservative for water treatment, mining, textiles, pulp and paper and food processing. Confirm the required grade, then request a quotation with COA/TDS/SDS for bulk supply.

CAS: 7681-57-4
Synonyms: Sodium Pyrosulfite, Disodium Metabisulfite, Sodium Disulfite, Disodium Pyrosulfite
Einecs: 231-673-0
Molecular Formula: Na₂S₂O₅
Grade: Industrial Grade / Food Grade
Package: 25kg PP/PE liner bags, 500kg/1000kg Jumbo bags (Customizable)

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Product Description

Sodium Metabisulfite, CAS 7681-57-4, also known as sodium pyrosulfite or disodium metabisulfite, is the inorganic sulfite salt Na₂S₂O₅; the EC/EINECS number is 231-673-0.

Synonyms: sodium pyrosulfite; disodium metabisulfite; sodium disulfite; disodium pyrosulfite.

CAS: 7681-57-4.

Molecular formula: Na₂S₂O₅.

Molecular weight: 190.11 g/mol.

EC number: 231-673-0.

It is a white to slightly yellow crystalline powder with a slight sulfur dioxide odor and high water solubility.

It dissolves to form bisulfite and sulfite species and can release sulfur dioxide, especially in acidic solution.

It is a strong reducing agent and oxidizes readily to sodium sulfate in moist air.

It is used for dechlorination of process water, wastewater and reverse-osmosis feed water, and to reduce hexavalent chromium to trivalent chromium.

It is used in mining as a depressant and flotation agent, especially in gold recovery and copper/lead/zinc ore processing.

It is used in textile bleaching, antichlor treatment, pulp and paper bleaching, leather processing and photography.

Food grade is used as a permitted preservative, antioxidant and color fixative, often associated with E223.

Confirm grade, Na₂S₂O₅ purity, SO₂ content, pH, iron, heavy metals, arsenic and water-insoluble matter.

Store in tightly closed containers in a cool, dry, dark warehouse, away from oxidants, strong acids and heat sources.

Never store with acids, as toxic sulfur dioxide gas is released; keep the product below about 25 °C where practical.

Confirm packaging with the requested quantity and destination requirements.

The page is an RFQ entry point and does not state stock, price, MOQ or fixed lead time.

For an RFQ, state the intended use, required grade, quantity, packaging, destination and document needs.

FAQ - Technical & Supply Chain

Q:
What is Sodium Metabisulfite CAS 7681-57-4?

A: Sodium metabisulfite, also called sodium pyrosulfite or disodium metabisulfite, is an inorganic sulfite salt with the formula Na2S2O5. It is supplied as a white to slightly yellow crystalline powder and acts as a reducing agent, antioxidant, preservative and dechlorination agent.
Q:
Why is Sodium Metabisulfite used in water treatment?

A: It rapidly reduces free chlorine and chloramines to chloride, making it useful for dechlorination of process water, wastewater and reverse-osmosis feed water. It can also reduce hexavalent chromium to trivalent chromium in some wastewater treatment systems.
Q:
What happens when Sodium Metabisulfite dissolves in water?

A: It dissolves to form bisulfite and sulfite species and can release sulfur dioxide, especially in acidic solution. The resulting solution is reducing and has antimicrobial activity, so dosing should be controlled to avoid excess sulfite or sulfur dioxide.
Q:
Is Sodium Metabisulfite available as food grade?

A: The listing covers industrial and food grades. Food-grade sodium metabisulfite is used as a permitted preservative and antioxidant where regulations allow, often associated with E223, but sulfite sensitivity, labeling and destination-market limits must be considered.
Q:
What are the main industrial applications of CAS 7681-57-4?

A: Typical uses include water and wastewater dechlorination, textile bleaching and antichlor treatment, pulp and paper, leather processing, photography, gold recovery or cyanide treatment, and other chemical reduction processes.
Q:
Which specifications should I check before ordering Sodium Metabisulfite?

A: Confirm the grade, Na2S2O5 purity, SO2 content, pH, iron, heavy metals, arsenic and water-insoluble matter. Food-grade material should also meet the preservative purity limits and regulatory requirements of the destination market.

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