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Sodium carbonate, anhydrous

(soda ash)

CAS no: 497-19-8   Formula: Na2CO3   Molecular weight: 105.989

Physical Data

Appearance: White hygroscopic powder

Melting point: 858C
Boiling point: -

Density: 2.54 g/cm3
Solubility: 30.7 g/100 g H2Ograph

Thermodynamic Data

Enthalpy of formation: -
Gibbs energy of formation: -

Entropy: -
Heat capacity: -

Production and preparation

Previously, sodium carbonate was obtained from seaweed ashes, which the name 'soda ash' was derived. The substance can now be obtained from several mineral sources such as trona, Na2CO3.NaHCO3.nH2O, and natron, Na2CO3.


Natron, a powdery mass, encased in a plastic cover, to prevent adsorption of moisture. It is obtained from British Columbia.

Alternatively, it can be obtained from the ammonia-soda (Solvay) process. It was first carried out successfully in Belgium in the 1860s to produce sodium carbonate. It was patented in 1861 by the Belgian chemist Ernest Solvay (1838-1922). In this process, a concentrated brine is treated with ammonia and carbon dioxide (from calcium carbonate) to give sodium bicarbonate and ammonium chloride. The anhydrous carbonate is produced by simply heating sodium bicarbonate. Ammonia is recovered when ammonium chloride is heated with lime.

Solvay process

Behavior and Chemical Properties

Anhydrous sodium carbonate is stable to heat and does not decompose even when it is heated to redness. It is hygroscopic, which on exposure to moist air readily turns to sodium carbonate monohydrate. It is soluble in water but only slightly in alcohol.

It behaves as a weak alkali when dissolves in water. For example, in 19% aqueous solution the pH ~11.5. It reacts with acids to release carbon dioxide.

sodium carbonate and acid reaction

When carbon dioxide is bubbled into a carbonate solution, sodium bicarbonate (hydrogen carbonate) is formed:

sodium bicarbonate

History and Uses

Sodium carbonate is one of the most important starting materials in chemical manufacturing. The anhydrous compound is used in making glass, processing wood pulp, detergents and cleaners.

In the laboratory, sodium carbonate is used in volumetric analysis to standardize acids, and in qualitatively way, for testing cations. This is because sodium carbonate solution gives precipitates for salts of many metals as the metal carbonate or basic carbonate. In the case of insoluble salts (such as barium sulfate), it is fused with solid sodium carbonate. Potassium carbonate is usually added to lower the melting point (fusion mixture).

Hazard, Storage and Handling

Keep in a tightly closed container and isolate from incompatible substances, such as strong acids and aluminium. Dust is dry and fine and ensure the container is stored in a cool, dry and well-ventilated area.

Cause eye irritation and upon prolonged exposure may result skin irritation. It is only slightly toxic but harmful when ingested in large doses. The symptons may include abdominal pain, vomiting, diarrhea and even death. Inhalation of dust may aggravate asthma and other chronic pulmonary diseases. The oral LD50 for rats is 3160 mg/kg.

Upon spillage, splash the affected area with plenty of water. If swallowed, give plenty of water or milk to drink and seek medical advice. Do not induce vomiting. Do not give acidic fluids such as carbonated drinks or vinegar. Avoid breathing dust.

(Last update: March 2006)

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