Baking Soda and Sodium Chloride

Sodium chloride(NaCl)

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.

Properties

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.

Uses

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.

Preparation

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

Uses

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.