Sodium: Extraction, Physical and Chemical Properties, Uses

Extraction of Sodium

Down's process : It is now manufactured by electrolysis of fused sodium chloride.

Down's electrolytic cell, consists of an iron box through the bottom of which rises a circular carbon anode. The anode is surrounded by a ring shaped iron cathode enclosed in a wire gauze shell which also acts as a partition and separates the two electrodes.

On electrolysis, chlorine is liberated at the anode and let out through an exit at the top. Sodium is liberated at the cathode and remains in the wire-gauze shell. Level of molten sodium rises and it overflows into a receiver.

2 NaCl  -- >   2Na + Cl2

Physical properties

1.     It is a silvery white metal when freshly cut but is rapidly tarnished in air. It forms tetragonal crystals.

2.     It is a soft metal.

3.     It is a good conductor of electricity.

4.     It dissolves in liquid ammonia forming an intense blue solution.

Chemical properties

1) Action of air : In moist air a layer of sodium oxide, hydroxide and carbonate is formed on its surface which loses its lustre.

4Na + O_{2 -- >} 2 Na₂O --  (2H2O) -- > 4NaOH --- (2CO2 ) -- > Na₂CO₃ + 2H₂O

When heated in air, it burns violently to form the monoxide and the peroxide.

4 Na + O_{2 -- >} 2Na₂O

2)  Action  of water :  It  decomposes  water  vigorously,  liberating hydrogen and forming sodium hydroxide.

2 Na + 2 H2O -- > 2 NaOH + H2

3) Action of ammonia: Sodium gives sodamide with ammonia liberating hydrogen.

2 Na + 2NH3  -- -(570-670K)-- >   2 Na NH2 + H2.

Sodium dissolved in liquid ammonia is used as a reducing agent in organic chemistry.

4.Action of acids: It displaces hydrogen from acids 

2 HCl + 2 Na  -- >  2 NaCl + H2.

2 Na + 2NH3  -- -(570-670K)-- >   2 Na NH2 + H2.

Sodium dissolved in liquid ammonia is used as a reducing agent in organic chemistry.

5.Reducing action: Reduces many compounds when heated with them in the absence of air

Al₂O₃ + 6 Na  --- >     2 Al + 3 Na₂O

SiO₂ + 4Na  -- >  Si + 2 Na₂O.

Reduces carbondioxide when heated forming carbon and sodium carbonate.

4 Na + 3 CO_{2 -- >}  2 Na₂CO₃ + C.

6.With Mercury : When heated with mercury, sodium forms an amalgam of varying composition Na₂Hg, Na₃Hg, NaHg etc.

Uses

1.    For the preparation of sodium peroxide, sodamide and sodium cyanide, tetraethyl lead etc.

2.    Sodium amalgam is employed as a reducing agent.

3.    As a deoxidizing agent in the preparation of light alloys and some rare earth metals from their oxides.

4.    It acts as a catalyst in the polymerisation of isoprene (C5H3) into artificial rubber.

5.    As a reagent in organic chemistry.