How to Make Sodium Metabisulfite

Disclaimer: This guide is for informational purposes only. Working with chemicals can be hazardous. Perform experiments only in a properly equipped laboratory with appropriate safety measures and under expert supervision.

Required Materials

• Sodium carbonate (Na2CO3) or sodium hydroxide (NaOH)
• Sulfur dioxide gas (SO2)
• Water
• Protective gear (goggles, gloves, lab coat)

Chemical Reactions

Step 1: Generation of sodium bisulfite (NaHSO3):
Na2CO3 + SO2 + H2O → 2 NaHSO3
or
2 NaOH + SO2 → Na2SO3 + H2O then Na2SO3 + SO2 + H2O → 2 NaHSO3

Step 2: Conversion to sodium metabisulfite (Na2S2O5):
2 NaHSO3 → Na2S2O5 + H2O (by heating)

Procedure

• 1. Prepare Sodium Bisulfite Solution:
  
  • Dissolve sodium carbonate or sodium hydroxide in distilled water.
  • Bubble sulfur dioxide gas slowly through the solution with constant stirring until the pH drops to about 5. (Use pH paper to monitor.)
• 2. Isolate Sodium Bisulfite:
  
  • The solution now contains sodium bisulfite. Filter if necessary to clear impurities.
• 3. Convert to Sodium Metabisulfite:
  
  • Evaporate water carefully from the solution (by gentle heating under reduced pressure, if possible).
  • As the solution dries, sodium bisulfite partially converts to sodium metabisulfite.
  • Further heat the solid residue at around 150 °C to complete the conversion to sodium metabisulfite.
• 4. Cool and Store:
  
  • Allow to cool in a dry, air-tight container. Sodium metabisulfite is hygroscopic and should be stored away from moisture.

Safety Precautions

• Work in a well-ventilated area or fume hood.
• Sulfur dioxide gas is toxic; avoid inhalation at all times.
• Wear gloves, goggles, and a lab coat.
• Dispose of any waste safely, following local regulations.

Notes

• This procedure involves hazardous chemicals; professional knowledge is recommended.
• Sulfur dioxide is best sourced from gas cylinders with proper equipment or generated in situ.