Preparation of Sodium Metabisulfite

Sodium metabisulfite (Na2S2O5) is a white, crystalline chemical commonly used as a disinfectant, antioxidant, and preservative agent. Its preparation involves the reaction between sodium carbonate or sodium hydroxide and sulfur dioxide.

Materials Required

  • Sulfur dioxide gas (SO2)
  • Sodium carbonate (Na2CO3) or Sodium hydroxide (NaOH)
  • Distilled water
  • Beaker
  • Stirring rod
  • Protective gloves and goggles

Chemical Reaction

The reaction using sodium carbonate:

Na2CO3 + 2 SO2 → Na2S2O5 + CO2

Alternatively, using sodium hydroxide:

2 NaOH + 2 SO2 → Na2S2O5 + H2O

Procedure

  • Step 1: Dissolve sodium carbonate or sodium hydroxide in a sufficient amount of distilled water in a beaker.
  • Step 2: Bubble sulfur dioxide gas slowly through the solution while stirring constantly. Perform this step in a well-ventilated area or fume hood, as SO2 is toxic.
  • Step 3: Continue until no more SO2 is absorbed and precipitation is observed.
  • Step 4: Allow the solution to cool so sodium metabisulfite crystals form.
  • Step 5: Filter out the solid sodium metabisulfite, wash with a small amount of cold distilled water, and dry the product.

Safety Notes

  • Always wear gloves and goggles; handle SO2 with care.
  • Work in a fume hood or well-ventilated area to avoid inhalation.
  • Dispose of all chemicals and waste properly.

Conclusion

Sodium metabisulfite can be easily prepared in the laboratory using the reaction between sodium carbonate or sodium hydroxide and sulfur dioxide. Ensure all safety protocols are strictly followed during preparation.