Sodium trioxocarbonate (IV) exists as an anhydrous and also as an hydrated salt. Sodium trioxocarbonate (IV) decahydrate (Na2CO3.10H2O) is known as washing soda while the anhydrous salt (Na2CO3) is called soda ash.
Manufacture of Sodium Trioxocarbonate (IV)
This is known as Ammoniacal-soda Process or Solvay Process. Brine is a concentrated solution of sodium chloride.
Ammoniacal brine (NaCl + NH3) in water is fed into the tower. CO2 is subjected through the lower part of the tower. CO2 comes in contact with the ammoniacal brine. A precipitate of NaHCO3 is formed.
NaCl + NH3 + H2O + CO2 → NaHCO3 + NH4Cl
The NaHCO3 is filtered off and rinsed. On heating it decomposes to yield anhydrous sodium trioxocarbonate (IV), Na2CO3.
NaHCO3 → Na2CO3 + H2O + CO2
Soda ash, Na2CO3 is dissolved in hot water and recrystalled as washing soda.
Na2CO3 + 10H2O → Na2CO3.10H2O
Properties of Na2CO3
1. Na2CO3 is a white crystalline solid, which can exist as anhydrous salt (Na2CO3), or in many hydrated forms e.g. monohydrate salt (Na2CO3.H2O) and decahydrate (Na2CO3.10H2O – washing soda).
2. On heating, the decahydrate salt gradually loses water to finally give anhydrous salt (Na2CO3 – soda ash).
3. Na2CO3 is readily soluble in water to form weakly acidic trioxocarbonate (IV) acid and the strong base, sodium hydroxide. The solution of Na2CO3 reacts with many acids.
4. Na2CO3 does not decompose on heating.
Uses of Na2CO3
1. For the manufacture of glass.
2. For washing purposes in laundries.
3. As a household cleansing agent.
4. In paper and soap/detergent industries.
5. For the softening of water.
6. In textile industry and petroleum refining.
7. For the manufacture of other sodium compounds like sodium hydroxide, hypo, etc.
Evaluation Questions:
1. What are the alkali metals?
2(a). Describe the storage of sodium metal.
(b). Briefly describe the preparation of sodium trioxocarbonate (IV).
3(a). Give three uses of sodium hydroxide.
(b). Mention three physical properties of sodium.
(c). Describe the extraction of sodium.
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