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Starting with sodium chloride how would you proceed to prepare sodium metal sodium hydroxide sodium

10.16 Starting with sodium chloride how would you proceed to prepare (i) sodium metal (ii) sodium hydroxide (iii) sodium peroxide (iv) sodium carbonate ?

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R Rakesh

(i) Sodium metal can be extracted from sodium chloride.In this process electrolysis of fused NaCl(40%) and CaCl_{2}(60%) at a temp. of 1123K in Downs cell.

steel cathode and graphite block is act as anode. sodium and calcium deposit at cathode .

NaCl\rightarrow Na^{+}+Cl^{-}  (Molten state)

At Cathode-Na^{+}+e^{-}\rightarrow Na

At Anode-        \\Cl^{-}\rightarrow Cl+e^{-}\\ Cl+Cl\rightarrow Cl_{2}

(ii) NaOH can be prepared by the electrolysis of sodium chloride. By Castner- kellner process.  A brine solution is electrolysed using a mercury cathode and a carbon anode. Sodium metal discharged at the cathode combines with mercury to form sodium amalgam. Chlorine gas is evolved at the anode.

At Cathode   Na^{+}+e^{-}\rightarrow Na-amalgam

At anode-  Cl^{-}\rightarrow 1/2Cl_{2}+e^{-}

 

(iii) NaCl is electrolysed for the formation of Na metal (in downs process). this sodium metal is then heated on aluminium trays  in air to form sodium peroxide.

2Na+O_{2}\rightarrow Na_{2}O_{2}

(iv) Sodium carbonate is preapred by solvay process.NaHCO_{3} is precipitated in a reaction of sodium chloride and ammonium hydrogen carbonate.

\\2NH_{3} +H_{2}O+CO_{2}\rightarrow (NH_{4})_{2}CO_{3}\\ (NH_{4})_{2}CO_{3}+H_{2}O+CO_{2}\rightarrow NaHCO_{3}\\ (NH_{4})_{2}CO_{3} +NaCl\rightarrow NH_{4}Cl+NaHCO_{3}

this NaHCO_{3} crystals are heatedto give sodium carbonate.

2NaHCO_{3}\rightarrow Na_{2}CO_{3}+CO_{2}+H_{2}O

 

 

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