Science: Acids, Bases and Salts: Baking and Washing Soda, Plaster of Paris and Bleaching Powder (For CBSE, ICSE, IAS, NET, NRA 2022)

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Some Commonly Used Salts Are

Baking Soda

Chemically baking soda is sodium hydrogen carbonate, NaHCO3.

Baking Soda

Raw materials required:-The raw materials required to manufacture washing soda are: Limestone, which is calcium carbonate, CaCO3 Sodium chloride (NaCl) in the form of brine (Conc. NaCl Solution) Ammonia (NH3)

Process

In Solvey՚s process, carbon dioxide is obtained by heating limestone strongly, CaCO3 (s) ⎯ ⇾ CaO (s) + CO2 (g) ↑ lime stone quick lime carbon dioxide It is then passed through cold brine (a concentrated solution of NaCl in water) which has previously been saturated with ammonia, NaCl (aq) + CO2 (g) + NH3 (g) + H2O (l) ⎯ ⇾ NaHCO3 (s) ↓ + NH4Cl (aq) sodium chloride ammonia sodium hydrogen ammonium in brine carbonate chloride NaHCO3 is sparingly soluble in water and crystallizes out as white crystals. Its solution in water is basic in nature. It is a mild and non-corrosive base. Action of heat: On heating, sodium hydrogen carbonate is converted into sodium carbonate and carbon dioxide is given off, 2NaHCO3 heat ⎯⎯⎯ ⇾ Na2CO3 + H2O + CO2↑

Uses

  • Used for cooking of certain foods.
  • For making baking power (a mixture of sodium hydrogen carbonate and tartaric acid) . On heating during baking, baking soda gives off carbon dioxide. It is this carbon dioxide which raises the dough.
  • In medicines Being a mild and non-corrosive base, baking soda is used in medicines to neutralize the excessive acid in the stomach and provide relief.
  • In soda acid fire extinguishers.

Washing Soda

  • Chemically, washing soda is sodium carbonate decahydrate, Na2CO3.10H2O.
  • Manufacture Washing soda is manufacturing by Solvey՚s process. We have already learnt about the raw materials required and part of the process in the manufacture of baking soda. Sodium carbonate is obtained by calcination (strong heating in a furnace) of sodium hydrogen carbonate and then recrystallizing from water: 2NaHCO3 heat ⎯⎯⎯ ⇾ Na2CO3 + H2O + CO2 Na2CO3 + 10H2O ⎯ ⇾ Na2CO3.10H2O sodium carbonate washing soda

Uses

  • It is used in the manufacture of caustic soda, glass, soap powders, borax and in paper industry.
  • For removing permanent hardness of water.
  • As a cleansing agent for domestic purpose.

Plaster of Paris

  • Chemically, it is 2CaSO4. H2O or CaSO4.1 2 H2O (calcium sulphate hemi hydrate)
  • Manufacture Raw material Gypsum, (CaSO4.2H2O) is used as the raw material.
  • Process The only difference between gypsum (CaSO4.2H2O) and plaster of Paris (CaSO4.1/2H2O) is in the less amount of water of crystallization. When gypsum is heated at about 100° (373 K) temperature, it loses a part of its water of crystallization to form: CaSO4.2H2O () heat 100°C 373 K ⎯⎯⎯⎯⎯⎯ ⇾ CaSO4.1/2H2O + 3/2H2O

Uses

  • In making casts for manufacture of toys and statues.
  • In medicine for making plaster casts to hold fractured bones in place while they set. It is also used for making casts in dentistry.
  • For making the surface of walls and ceiling smooth.
  • For making decorative designs on ceilings, walls and pillars.
  • For making ‘chalk’ for writing on blackboard.
  • For making fireproof materials.

Bleaching Powder

  • Chemically, it is calcium oxychloride, CaOCl2.
  • Raw material required: The raw material required for the manufacture of bleaching powder are: Slaked lime, Ca (OH) 2 Chlorine gas, Cl2 Waste gases Slaked lime Chlorine Bleaching powder.
  • Process: It is manufactured by Hasen-Clever Method. The plant consists of four cylinders made of cast iron with inlet for chlorine near the base. The dry slaked lime, calcium hydroxide is fed into the chlorinating cylinders from the top. It moves down slowly and meets the upcoming current of chlorine. As a result of the reaction between them, it is converted into bleaching power which collects at the bottom.
  • Ca (OH) 2 + Cl2 ⎯ ⇾ CaOCl2 + H2O slaked lime chlorine bleaching powder (

Uses

  • In textile industry for bleaching of cotton and linen.
  • In paper industry for bleaching of wood pulp.
  • In making wool unshrinkable.
  • Used as disinfectant and germicide for sterilization of water.
  • For the manufacture of chloroform. 6. Used as an oxidizing agent in chemical industry.

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