I.  Explain  how  - 

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a.  Caustic soda is manufactured from common salt ?

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b.  Bleaching powder is obtained  ?

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c.  Plaster of paris obtained from gypsum  ?

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d. washing soda obtained ?

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e.  baking soda obtained  from  Nacl  ? 

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• Sodium hydroxide(Caustic soda):

It is produced from an aqueous solution of sodium chloride (called Brine). Electrolysis of brine (passing of electricity in a solution) results in the decomposition of sodium chloride and formation of sodium hydroxide. This process is also called chlor-alkali process (chlor for chlorine and alkali for NaOH). The reaction for the above process can be written as follows:

Hydrogen and chlorine gas are released at thecathode and anode respectively.

• Bleaching powder:

  Chlorine gas obtained in the electrolysis is used for the manufacture of bleaching powder. Chlorine gas on reacting with dry slaked lime [Ca(OH)₂] produces bleaching powder (CaOCl₂). The chemical equation involved in the reaction can be represented as:

  

• Baking soda:

  We know that baking soda is most commonly used in the kitchen for making delicious pakoras. The chemical name of baking soda is sodium hydrogen carbonate (NaHCO₃). Baking soda is produced by using sodium chloride as one of the raw materials. The chemical equation can be represented as follows:

  

• Washing soda:

  Washing soda is also produced from common salt. The chemical name of washing soda is hydrated sodium carbonate and its chemical formula is Na₂CO₃.10H₂O. It is obtained by heating sodium hydrogen carbonate.

  

  The re-crystallization of sodium carbonate produces washing soda.

  

• When hydrated calcium sulphate (CaSO₄.2H₂O) or gypsum is heated at 373K, it loses its water molecules and forms calcium sulphate hemihydrate (). This hemihydrated form of calcium sulphate is known as Plaster of Paris. It is in the form of a white powder.