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COMPOUNDS OF ALKALI METALS

 COMPOUNDS OF ALKALI METALS 

1. Sodium (Na) , Natrium 

  • Extraction of sodium  : Down's Process
 By Electrolysis of fused NaCl + CaCl2 + NaF 
At cathode (Iron Vessel) : Na+ +e– ⟶  Na(s) 
At Anode (Graphite) : 2Cl–   →    Cl 2 + 2e– 
(i) (CaCl2 + NaF) is used to lower Melting point (8000 C) of NaCl to about 6000 C. 
(ii) Aqueous sodium chloride cannot be used for preparing sodium by electrolysis. Because instead of metallic sodium, hydrogen gas will be liberated at cathode.

  • Properties sodium , Natrium

(i) sodium is a crystalline soft metal. 

(ii) Highly reactive, so kept in kerosene. 

(iii) Na dissolves in liquid NH3 to give blue solution. 

  • Uses of sodium , natrium 

(i) In the preparation of sodium amalgam (used as reducing agent)

 (ii) In sodium vapour lamp, which emits monochromatic yellow light. 

(iii) As heat transfer medium in nuclear reactors.

2. Sodium chloride NaCl

  • Occurrence of sodium chloride (NaCl)
 Sea water is the main source and also found in salt lakes.

  • Preparation sodium chloride (NaCl)
(i)Sea water NaCl(2.7 – 2.9%) Evaporation by solar heat crude NaCl 

(ii) It contains impurities – Na2 SO4 , MgCl2 , CaCl2 etc.

(iii) Insoluble impurities removed by filtration. 

(iv) Filtrate (HCl gas passed)→ Pure NaCl precipitation (Common ion effect)

HCL⇌  H+    +Cl-                                   

NaCl ⇌Na+    + Cl -

Ionic product of [Na+ ] [Cl– ] > solubility product of NaCl hence it precipitates out. 

(v) MgCl2 and CaCl2 are more soluble in water so left in solution.

  •  Properties of sodium chloride (NaCl)
(i) Table salt is slightly hygroscopic due to the presence of magnesium and calcium chlorides in small amounts. 

(ii) Reaction with AgNO3 

NaCl + AgNO3 → NaNO3 + AgCl(white ppt.) 

Reaction with K2Cr2O7 + conc. H2SO4 

(iii) 4NaCl + K2Cr2O7 + 5H2SO4 →(heat )4NaHSO4 + K2SO4 + 2CrO2Cl2 (orange red) + 3H2O 

  • Uses of sodium chloride (NaCl) 

(i) As a preservative for pickles, meat and fish. 

(ii) For making freezing mixture with Ice. 

 3.SODIUM HYDROXIDE (NaOH), CAUSTIC SODA

  • Manufacture of sodium hydroxide (NaOH) : By electrolysis of NaCl. 
  • Nelson Cell or Diaphragm Cell : The following reactions takes place – 



At cathode (Perforated steel) : 2H+ + 2e– ⟶ H2 (g)
At anode (Carbon) : 2Cl– (aq.) ⟶  Cl2 (g) + 2e–

  •  Castner – Kellner Cell : (Hg – Cathode Process) 
Electrolite (Brine) NaCl ⇌ Na+  + Cl-

 On electrolysis –

At Cathode (Hg) 

Na+ + e– ⟶ Na. and Na + Hg ⟶ Na.Hg (amalgum)

At anode (Graphite) 

2Cl– ⟶Cl2 (g) + 2e– and 2Na.Hg + 2H2O ⟶ 2NaOH + H2 + 2Hg

  • Properties of sodium hydroxide (NaOH)  
(i) It is deliquescent white crystalline solid. 

(ii) It absorbs CO2 from air forming Na2CO3 . 

(iii) NaOH is strong base

(iv) Reaction with non metals : no reaction with H2 , N2 and C

(v) Reaction with halogens

vi) Reaction with Metal :

(vii) Reaction with ZnCl2 or ZnSO4

viii) The hydroxides of aluminium, zinc, lead and tin, however, dissolve in excess of sodium hydroxide giving clear solution which can also be obtained when these metals are acted upon by the concentrated solution of sodium hydroxide.


  • Uses of Sodium hydroxide (NaOH)
(i) In the manufacture of soap, rayon, dyes, paper and drugs. 
(ii) In petroleum refining.

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