Sodium Carbonate

At room temperature, sodium carbonate (Na₂CO₃) is an odorless, grayish white powder which is hygroscopic. This means when it is exposed to air, it can spontaneously absorb water molecules. Another familiar compound that has this hygroscopic quality is sugar. Sodium carbonate has a melting point of 1,564°F (851°C), a density of 2.53 g/cm³, and is soluble in water. A water solution of soda ash has a basic pH and a strong alkaline taste. When it is placed in a slightly acidic solution, it decomposes and forms bubbles. This effect, called effervescence, is found in many commercial antacid products which use sodium carbonate as an active ingredient.

Anhydrous (without water) sodium carbonate can absorb various amounts of water and form hydrates which have slightly different characteristics. When one water molecule per molecule of sodium carbonate is absorbed, the resulting substance, sodium carbonate monohydrate, is represented by the chemical formula Na₂CO₃ • H₂O. This compound has a slightly lower density than the anhydrous version. Another common hydrate is formed by the absorption of ten water molecules per molecule of sodium carbonate. This compound, Na₂CO₃• 10H₂O, known as sodium carbonate decahydrate, exists as transparent crystals which readily effervesce when exposed to air.