The Story Of Washing Soda

What is Washing soda [\( Na_2CO_3.10H_2O\)] ?

Washing soda finds its application in numerous ways, be it from household uses to a vast range of industrial applications. It is an alkaline compound with a high alkaline character which has the capability to remove adamant stains from clothes during washing. Chemically washing soda is a hydrated salt of sodium carbonate with a chemical formula –\( Na_2CO_3.10H_2O\)

Solvay Process- Preparation of Sodium Carbonate

Steps involved in the manufacture of sodium carbonate are explained below:

  • Purification of Brine
  • Formation of sodium hydrogen carbonate
  • Formation of sodium carbonate
  • Recovery of ammonia

Step 1: Purification of Brine

Concentrated brine is obtained by the process of evaporation and impurities like calcium, magnesium etc are removed by the process called precipitation. The concentrated brine solution undergoes filtration and is mixed with ammonia in the ammonia tower and the ammonia tower gets cooled.

Step 2: Formation of sodium hydrogen carbonate

In a carbonate tower, carbon dioxide is passed through ammoniated brine solution.

\(NH_3 (aq) + CO_2 (g) + NaCl (aq) + H_2O \rightarrow  NaHCO_3(s) + NH_4Cl (aq)\)

Step 3: Formation of sodium carbonate

Sodium Bicarbonate formed is obtained from the tower and is heated at a temperature of 300°C. Hence formations of sodium carbonate take place.

\( 2NaHCO_3 \rightarrow Na_2CO_3 + CO_2 + H_2O \)

Step 4: Recovery of ammonia

Ammonia can be recovered by treating the solution of NH4Cl with Ca (OH)2. This ammonia is again used in the Solvay process and CaCl2 is obtained as a by-product.

\( 2NH_4Cl + Ca (OH)_2 \rightarrow 2NH_3 + CaCl_2 + H_2O\)

Physical properties and chemical properties of sodium carbonate:

  • It is a crystalline solid which is white in color.
  • It exists as a monohydrated salt (\(Na_2CO_3.10H_2O\)), anhydrous salt (\(Na_2CO_3\)) ,  heptahydrous salt (\(Na_2CO_3.7H_20\)) and decahydrate salt (\(Na_2CO_3.10H_2O\)).
  • Sodium carbonate is basic in nature.
  • It has a melting point of 851°C.
  • In the presence of heat, it loses its water to form an anhydrous salt (soda ash).
    \(Na_2CO_3.10H_2O ~ \overset{373k}{\rightarrow} ~Na_2CO_3.H_2O ~ \overset{373k}{\rightarrow} ~Na_2CO_3\)

Uses of Washing Soda:

  • Used as a cleansing agent in industries and household.
  • It finds its application in paper, textile, soap, and detergent industries.
  • It is used in the process of softening of water.
  • It is used in the manufacturing of glass.
  • It is one of the most important agents in laundries.

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