The most abundant source of sodium chloride is sea water which contains 2.7-2.9% by mass.
Common salt is generally obtained by evaporation of sea water. Crude sodium chloride obtained by crystallisation of brine solution contains impurities of sodium sulphate (Na2SO4) , calcium sulphate (CaSO4 ) , calcium chloride (CaCl2) magnesium chloride (MgCl2).
Since MgCl2 and CaCl2 are deliquescent (absorb moisture easily from the atmosphere), therefore , impure common salt gets wet in rainy season. To obtain pure sodium chloride , the crude salt is dissolved in minimum amount of water and filtered to remove insoluble impurities. The solution is then saturated with HCl gas when crystals of pure sodium chloride separates out. The solution is then saturated with hydrogen chloride gas when crystals of pure sodium chloride separates out. The calcium and magnesium chloride being more soluble remains in the solution.
1) Sodium chloride melts at 1081 K.
2) Its solubility is 3.6 g per 100 g of H2O at 273 K. The solubility does not increase appreciably with rise in temperature.
1) It is used as a common salt for domestic purpose.
2) It is used in the preparation of Na2CO3 , NaOH, Na2O2.
Baking soda or Sodium hydrogen carbonate(NaHCO3)
Sodium hydrogen carbonate is commonly called Baking soda because on heating it decomposes to evolve bubbles of carbon dioxide.
It is prepared by saturating a solution of sodium carbonate with carbon dioxide. Being less soluble, white crystalline powder of sodium hydrogen carbonate gets separated.
Na2CO3 + CO2 + H2O ———> 2 NaHCO3
1) It is used in fire extinguishers for generating CO2.
NaHCO3 + HCl ————-> NaCl + CO2 + H2O
2) It is used in the preparation of baking powder which is a mixture of NaHCO3 , starch, calcium dihydrogen phosphate Ca(H2PO4)2 , sodium Aluminium Sulphate NaAl(SO4)2.
3) It is a mild antiseptic for skin infections.
4) It is used as an antacid in making digestive powders for removing acidity of stomach.