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ChemistryEdu Logo Alkali Metals | Some Important Compounds of Sodium#

In this article, we will discuss some important compounds of sodium like washing soda, sodium chloride, caustic soda and baking soda.

Washing Soda (Na2CO3.10H2O)#

  • Sodium carbonate is a white crystalline solid which exists as a decahydrate, Na2CO3.10H2O. This is known as washing soda.

  • Washing soda is readily soluble in water.

  • When washing soda is heated, it forms monohydrate.

\[Na_2CO_3.10H_2O + Heat → Na_2CO_3.H_2O + 9H_2O\]
  • When washing soda is heated above 373 K, it forms sodium carbonate or soda ash which is a white powder.
\[Na_2CO_3.H_2O + Heat (> 373K) → Na_2CO_3 + H_2O\]
\[Na_2CO_3.10H_2O + Heat (> 373K) → Na_2CO_3 + 10H_2O\]

Preparation of Sodium Carbonate#

  • Sodium carbonate is prepared by solvay process.

Step I. Preparation of NaHCO3

\[2NH_3 + H_2O + CO_2 → (NH_4)_2CO_3\]
\[(NH_4)_2CO_3 + H_2O + CO_2 → 2NH_4HCO_3\]
\[2NH_4HCO_3 + NaCl → NH_4Cl + NaHCO_3 ↓\]

NaHCO3 is obtained as precipitate and it is separated out.

Step II. Heating of NaHCO3

\[2NaHCO_3 + Heat → Na_2CO_3 + H_2O + CO_2\]

In this process NH3 is recovered when NH4Cl is treated with Ca(OH)2.

\[2NH_4Cl + Ca(OH)_2 → 2NH_3 + CaCl_2 + 2H_2O\]

Note

It is important to note that solvay process is not used to prepare potassium carbonate because KHCO3 is too soluble in water.

Uses of washing soda#

  • Water softening, laundering and cleaning.
  • Manufacture of glass, soap, borax and caustic soda.
  • Used in paper, paints and textile industries.

Sodium Chloride (NaCl)#

  • Sodium chloride is known as common salt or table salt.
  • The solubility of NaCl does not increase appreciably with increase in temperature.

Preparation of Sodium Chloride#

  • Crude sodium chloride is obtained by crystallization of brine solution (concentrated NaCl solution).
  • Crude sodium chloride contains the following impurities: CaSO4, Na2SO4, CaCl2 and MgCl2. Both CaCl2 and MgCl2 are deliquescent, ie they absorb moisture.
  • Pure sodium chloride is obtained by dissolving crude NaCl in minimum amount of water and filtered to remove insoluble impurities.
  • This solution is saturated with HCl gas. Then crystals of pure NaCl are separated out.
  • Ca and Mg chloride are more soluble in solution than NaCl and these remained in the solution.

Uses of Sodium Chloride#

  • It is used as common salt or table salt.
  • It is used to prepare Na2O2, NaOH and Na2CO3.

Sodium Hydroxide (NaOH) or Caustic soda#

  • Caustic soda or sodium hydroxide is a white and translucent solid.
  • It melts at 591 K.
  • It is readily soluble in water and gives a strong alkaline solution.
  • Crystals of NaOH are deliquescent, ie, they absorb moisture.
  • Sodium hydroxide solution at the surface reacts with CO2 in the atmosphere to form Na2CO3.
\[2NaOH + CO_2 → Na_2CO_3 + H_2O\]

Preparation of Sodium Hydroxide#

Step I. Electrolysis of brine solution in Castner-Kellner cell

In Castner-Kellner cell, mercury is cathode and carbon is anode.

\[Cathode:\ Na^+ + e^- + Hg → Na-Hg\ (Sodium\ amalgam)\]
\[Anode:\ Cl^- → {1 \over 2}Cl_2 + e^-\]

Step II. The amalgam is treated with water to give sodium hydroxide and hydrogen.

\[2Na-Hg + 2H_2O → 2NaOH + 2Hg + H_2 ↑\]

Uses of Sodium Hydroxide#

  • It is used as a cleansing agent and in the manufacturing of washing soda.
  • It is used in the preparation of soda lime.
  • It is used in the extraction of aluminium by purifying bauxite.

Sodium Hydrogen Carbonate (NaHCO3) or Baking soda#

  • Sodium hydrogen carbonate is known as baking soda because it decomposes on heating to generate bubbles of CO2 leaving holes in cake or pastries and making them light and fluffy.
\[2NaHCO_3 + Heat → Na_2CO_3 + H_2O + CO_2\]

Preparation of Sodium Hydrogen Carbonate#

  • It is made by saturating a solution of sodium carbonate with carbon dioxide. The white crystalline powder of NaHCO3 being less soluble gets separated out.
\[Na_2CO_3 + H_2O + CO_2 → 2NaHCO_3 ↓\]

Uses of Sodium Hydrogen Carbonate#

  • It is used as a mild antiseptic for skin infections.

  • It is used in fire extinguishers because it generates CO2.

\[2NaHCO_3 + Heat → Na_2CO_3 + H_2O + CO_2\]
  • It can be used as an antacid which is used to treat stomach upset and indigestion.