The pH of Sodium Metabisulfite in Water

The pH of a sodium metabisulfite solution depends on its concentration. A 5% solution has a pH of 3.5-5.0, while a 10% solution has a pH of 4.0-5.0. Sodium metabisulfite is used as a disinfectant, antioxidant, and preservative agent. When dissolved in water, it generates bisulfite ions, which can react with water to form sulfurous acid and sodium hydroxide. This reaction can lower the pH of the solution, making it acidic.

Understanding the pH of Sodium Metabisulfite Solutions

The pH of a sodium metabisulfite solution is influenced by several factors:

  1. Concentration: The pH of the solution decreases as the concentration of sodium metabisulfite increases. A 5% solution has a pH range of 3.5-5.0, while a 10% solution has a pH range of 4.0-5.0.

  2. Reaction with Water: When sodium metabisulfite is dissolved in water, it generates bisulfite ions (HSO3-) that can react with water to form sulfurous acid (H2SO3) and sodium hydroxide (NaOH). This reaction can lower the pH of the solution, making it more acidic.

The reaction can be represented as follows:
Na2S2O5 + H2O → 2 NaHSO3
NaHSO3 + H2O ⇌ H2SO3 + NaOH

  1. pH Adjustment: The pH of a sodium metabisulfite solution can be adjusted by adding an acid or a base. For example, adding an acid will further lower the pH, while adding a base will increase the pH.

Preparing a Sodium Metabisulfite Solution

PH of sodium metabisulfite in waterImage source: OpenStax College

To prepare a solution of sodium metabisulfite, follow these steps:

  1. Determine the desired concentration of the solution.
  2. Calculate the amount of sodium metabisulfite required based on the desired volume and concentration.
  3. For a 1 M solution, you would need to dissolve 190.11 g of sodium metabisulfite in 1 L of water.
  4. Slowly add the calculated amount of sodium metabisulfite to the water, stirring continuously to ensure complete dissolution.
  5. Measure the pH of the solution and adjust it if necessary by adding an acid or a base.
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Applications of Sodium Metabisulfite

Sodium metabisulfite is used in various industries due to its disinfectant, antioxidant, and preservative properties:

  1. Water Treatment: Sodium metabisulfite is used to quench residual chlorine in water treatment processes.
  2. Food and Beverage Industry: It is added to foods and beverages to prevent browning and spoilage, and to remove excess sulfur dioxide in wine making.
  3. Pharmaceutical Industry: Sodium metabisulfite is used as a preservative and antioxidant in pharmaceutical products.
  4. Shipping and Storage: Plastic stickers and packaging containing sodium metabisulfite are used to inhibit the growth of microorganisms during shipping and storage of consumer goods.

Safety Considerations

When handling sodium metabisulfite, it is important to take the following safety precautions:

  • Wear appropriate personal protective equipment (PPE), such as gloves and goggles, to prevent skin and eye irritation.
  • Avoid heating or mixing sodium metabisulfite with strong acids, as this can produce toxic gases.
  • Ensure proper ventilation when working with sodium metabisulfite solutions, as they can be corrosive.
  • Follow all local regulations and guidelines for the safe handling and disposal of sodium metabisulfite.

Conclusion

The pH of a sodium metabisulfite solution is influenced by its concentration and the reaction with water, which can lower the pH and make the solution more acidic. Understanding the pH of sodium metabisulfite solutions is crucial for its various applications, such as water treatment, food and beverage preservation, and pharmaceutical formulations. By following the proper preparation and safety guidelines, sodium metabisulfite can be used effectively and safely in a wide range of industries.

References:

  1. Ward’s Science. (n.d.). Sodium Metabisulfite. Retrieved from https://www.wardsci.com/store/product/8887876/sodium-metabisulfite
  2. Wiley Online Library. (1968). The effect of pH and sodium metabisulphite on the stability of … Retrieved from https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.2042-7158.1968.tb09870.x
  3. NCBI. (n.d.). SODIUM METABISULFITE, SODIUM PYROSULFATE. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK216455/
  4. Honeywell Research Chemicals. (n.d.). Sodium metabisulfite. Retrieved from https://lab.honeywell.com/shop/sodium-metabisulfite-13459
  5. Wikipedia. (n.d.). Sodium metabisulfite. Retrieved from https://en.wikipedia.org/wiki/Sodium_metabisulfite
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