Sodium Carbonate Na2CO3.10H2O (Washing soda):
Sodium carbonate is one of the important inorganic compounds used in industries. It is prepared by Solvay process. In this process, ammonia is converted into ammonium carbonate which then converted to ammonium bicarbonate by passing excess carbon dioxide in a sodium chloride solution saturated with ammonia. The ammonium bicarbonate thus formed reacts with the sodium chloride to give sodium bicarbonate and ammonium chloride. As sodium bicarbonate has poor solubility, it gets precipitated. The sodium bicarbonate is isolated and is heated to give sodium carbonate. The equations involved in this process are,
2NH3 + H2O + CO2 → (NH4)2CO3
(NH4)2CO3 + H2O + CO2 → 2 NH4HCO3
2 NH4HCO3 + NaCl → NH4Cl + NaHCO3
2 NaHCO3 → Na2CO3 + CO2 + H2O
The ammonia used in this process can be recovered by treating the resultant ammonium chloride solution with calcium hydroxide. Calcium chloride is formed as a by-product.
Sodium carbonate, commonly known as washing soda, crystallises as decahydrate which is white in colour. It is soluble in water and forms an alkaline solution. Upon heating, it looses the water of crystallisation to form monohydrate. Above 373 K, the monohydrate becomes completely anhydrous and changes to a white powder called soda ash.
Na2CO3·10H2O → Na2CO3·H2O + 9H2O
Na2CO3·H2O → Na2CO3 + H2O
i. Sodium carbonate known as washing soda is used heavily for laundering
ii. It is an important laboratory reagent used in the qualitative analysis and in volumetric analysis.
iii. It is also used in water treatment to convert the hard water to soft water
iv. It is used in the manufacturing of glass, paper, paint etc...