Common salt — A raw material for chemicals:
The common salt thus obtained is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, bleaching powder and much more. Let us see how one substance is used for making all these different substances.
Chlorine gas is used for the manufacture of bleaching powder. Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2]. Bleaching powder is represented as CaOCl2, though the actual composition is quite complex.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Bleaching powder is used –
- for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in the laundry;
- as an oxidizing agent in many chemical industries; and
- for disinfecting drinking water to make it free of germs.
The soda commonly used in the kitchen for making tasty crispy pakoras is baking soda. Sometimes it is added for faster cooking. The chemical name of the compound is sodium hydrogen carbonate (NaHCO3). It is produced using sodium chloride as one of the raw materials.
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
Uses of sodium hydrogen carbonate (NaHCO3):
- For making baking powder, which is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. When baking powder is heated or mixed in water, the following reaction takes place –
NaHCO3 + H+ → CO2 + H2O + Sodium salt of acid
Carbon dioxide produced during the reaction causes bread or cake to rise making them soft and spongy.
- Sodium hydrogen carbonate is also an ingredient in antacids. Being alkaline, it neutralizes excess acid in the stomach and provides relief.
- It is also used in soda-acid fire extinguishers.
Another chemical that can be obtained from sodium chloride is Na2CO3.10H2O (washing soda). You have seen above that sodium carbonate can be obtained by heating baking soda; recrystallisation of sodium carbonate gives washing soda. It is also a basic salt.
Na2CO3 + 10H2O → Na2CO3.10H2O
Uses of washing soda:
- Sodium carbonate (washing soda) is used in glass, soap and paper industries.
- It is used in the manufacture of sodium compounds such as borax.
- Sodium carbonate can be used as a cleaning agent for domestic purposes.
- It is used for removing permanent hardness of water.