What is the Difference Between Sodium Bisulfite and Sodium Metabisulfite

Both sodium bisulfite and sodium metabisulfite are commonly used as food additives and industrial chemicals. These compounds are strong reducing agents and can be used to adjust the pH of solutions.

What is the difference between sodium bisulfate and sodium metabisulfite? Sodium bisulfite contains one sodium ion, one hydrogen ion, and one sulfite ion, while sodium metabisulfite has two sodium ions and one disulfite ion.

Key Areas Covered

1. What is Sodium Bisulfite 
      – Definition, Features, Uses
2. What is Sodium Metabisulfite
      – Definition, Features, Uses 
3. Similarities Between Sodium Bisulfite and Sodium Metabisulfite
      – Outline of Common Features
4. Difference Between Sodium Bisulfite and Sodium Metabisulfite 
      – Comparison of Key Differences
5. FAQ: Sodium Bisulfite and Sodium Metabisulfite
      – Answers to Frequently Asked Questions

Key Terms

Na2S2O5, NaHSO3, Sodium Bisulfite, Sodium Metabisulfite

What is Sodium Bisulfite

Sodium bisulfite, or NaHSO3, is a white or slightly yellowish crystalline solid, highly soluble in water. The strong reducing properties make the substance useful in various industries, including food processing, textile manufacturing, and water treatment.

The main use of sodium bisulfite is as a reducing agent. This property makes it capable of removing oxygen from solutions and reducing the oxidation state of other compounds. This property is useful in the textile industry to bleach fabrics and remove unwanted color.

Sodium bisulfite can also be used to adjust pH in water solutions. Weak acid sodium bisulfite reduces the pH of basic solutions. This property is useful in different chemical reactions and wastewater treatment.

Moreover, sodium bisulfite is approved as a food additive in many countries. It is used as a preservative, an antioxidant, and a bleaching agent, but its use is set under regulation criteria meant to curtail any potential hazard for people and prevent its over-consumption.

What is Sodium Metabisulfite

Sodium metabisulfite, Na2S2O5, is a white or slightly yellowish crystalline solid and very soluble in water. Metabisulphite is a powerful reducing agent that gives electrons to a variety of other substances. This property allows it to react with all oxidizing agents and reduce their state. Thus, this creates a substance that is very useful in a number of applications related to bleaching, as an antioxidant, or in wastewater treatment.

Sodium metabisulfite is generally accepted as a food additive across most nations. The product is used both as a preservative and an antioxidant in addition to being used as a bleaching agent. Its use is regulated to avoid excessive intake, which may prove hazardous to health.

In addition to food and water treatment, a few industrial uses of sodium metabisulfite also exist. This compound has applications in the paper and pulp industries and pharmaceutical preparations. It is used as a reducing agent and pH regulator within mining and metal refining industries.

Similarities Between Sodium Bisulfite and Sodium Metabisulfite

1. These compounds are strong reducing agents.
2. Both can adjust the pH of solutions.
3. Both compounds are approved as food additives in many countries.
4. These compounds can be irritating to the eyes, skin, and respiratory tract.

Difference Between Sodium Bisulfite and Sodium Metabisulfite

Definition

• Sodium bisulfite is a chemical compound (NaHSO₃) used as a preservative, disinfectant, and reducing agent in various industries, whereas sodium metabisulfite is a compound (Na₂S₂O₅) commonly used as a preservative, antioxidant, and disinfectant, often favored for its high sulfur dioxide content.

Composition

• Sodium bisulfite contains one sodium ion, one hydrogen ion, and one sulfite ion, whereas sodium metabisulfite contains two sodium ions and one disulfite ion.

Stability

• Sodium metabisulfite is generally more stable in solid form than sodium bisulfite.

Solubility

• Sodium metabisulfite is slightly less soluble in water than sodium bisulfite.

Reactivity

• Sodium metabisulfite tends to react more slowly than sodium bisulfite.

Conclusion

Both sodium bisulfite and sodium metabisulfite are common food additives, mostly used as preservatives and antioxidants. They have similar properties, but sodium metabisulfite is preferred because it contains a higher concentration of sulfur dioxide and can be used in smaller amounts while still being effective.

FAQ: Sodium Bisulfite and Sodium Metabisulfite

1. How to convert sodium metabisulfite to sodium bisulfite?

To convert sodium metabisulfite to sodium bisulfite, simply dissolve it in water. The reaction will produce sodium bisulfite and sulfur dioxide gas. The sulfur dioxide can be vented or absorbed using a suitable solution.

2. What is a substitute for sodium metabisulfite?

Sodium metabisulfite is commonly used as a preservative and antioxidant in various food and beverage products. Some potential substitutes for sodium metabisulfite include ascorbic acid (vitamin C), potassium sorbate, and citric acid.

3. Can I use sodium bisulfite instead of sodium metabisulfite?

Yes, you can often use sodium bisulfite instead of sodium metabisulfite. Sodium metabisulfite is a dehydrated form of sodium bisulfite. When dissolved in water, both compounds yield the same active ingredient, sulfurous acid.

4. What are the disadvantages of sodium bisulfite?

Sodium bisulfite can cause allergic reactions, especially in people with asthma. It can contribute to acid rain and water pollution. When used in the food industry, it can reduce the nutritional value of food, particularly vitamin B1. It may also cause discoloration or off-flavors in certain foods.

Reference:

1. “Sodium Bisulfite.” Wikipedia. Wikipedia Foundation. 
2. “Sodium Metabisulfite.” Wikipedia. Wikipedia Foundation.

Image Courtesy:

1. “Hydrogensiřičitan_sodný” By Milda 444 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Sodium-metabisulfite-2D” (Public Domain) via Commons Wikimedia