Sodium Carbonate (Soda Ash)

Products

Sodium carbonate or soda ash is available as a pure substance in pharmacies and drugstores. The various products differ in the bound crystal water. In pharmaceuticals, it is included as an excipient.

Structure and properties

Sodium carbonate (Na2CO3, Mr = 105.988 g/mol) exists as a white, crystalline, odorless, and highly hygroscopic powder that is readily soluble in water. It dissolves even more readily in warm or hot water. It is the disodium salt of carbonic acid and is therefore also called disodium carbonate. Anhydrous sodium carbonate has a high melting point of 851°C to 854°C. Sodium carbonate also occurs naturally as a mineral and is produced synthetically by the Solvay method. The pharmacopoeia recognizes three grades, which differ in the bound water of crystallization:

  • Anhydrous sodium carbonate (Natrii carbonas anhydricus) PhEur – Na2CO3
  • Sodium carbonate monohydrate (Natrii carbonas monohydricus) PhEur – Na2CO3 – H2O
  • Sodium carbonate decahydrate (Natrii carbonas decahydricus) PhEur – Na2CO3 – 10 H2O, crystal soda

Sodium carbonate, by the way, can be obtained from sodium hydrogen carbonate by heating. This produces the gas carbon dioxide and water:

  • 2 NaHCO3 (sodium hydrogen carbonate) Na2CO3 (sodium carbonate) + CO2 (carbon dioxide) + H2O (water)

This experiment is also exciting because gas bubbles form in the powder.

Effects

Sodium carbonate is a relatively strong base (pKb = 3.67). Adding 4 g to 1 L of water produces a solution with a pH above 11. It is milder than the corrosive sodium hydroxide (NaOH). The effects are due to the release of the hydroxide ion in aqueous solution. Sodium carbonate also has antiseptic properties. With an acid, carbon dioxide (CO2):

  • Na2CO3 (sodium carbonate) + 2 HCl (hydrochloric acid) 2 NaCl (sodium chloride) + H2O (water) + CO2 (carbon dioxide)

Fields of application

Small selection:

  • As a pharmaceutical excipient, for example, as an acidity regulator and in nicotine gum.
  • As a household cleaning agent, for example, for glasses, the oven and the drain.
  • For the preparation of lye pastries.

Undesirable effects

Due to its basicity, sodium carbonate may cause severe eye irritation. In case of accidental contact, rinse with running water for at least 10 minutes. Gently remove contact lenses and continue rinsing. Refer to the Material Safety Data Sheet for appropriate precautions.