Question

why alkali and alkaline earth metals be prepared by electrolysis of their aqueous haldie solution

Answer 1

Alkali metals cannot be obtained by the electrolysis of the aqueoussolution of their salts because H2 is liberated at cathode instead of alkali metal. That's why alkali metals are prepared by electrolysis of their fused chlorideThe alkali metals are very reactive and are strong reducing agents so they cannot be extracted by usual methods. ... Because themetals formed will react immediately react with water forming their hydroxides. Therefore these metals are generally isolated by theelectrolysis if their fused metals chlorides


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Compounds of the Alkaline Earth Metals

 

Table of Content

General Characteristics of Compounds of the Alkaline Earth Metals

Oxides of Alkali Earth Metals

Hydroxides of Alkali Earth Metals

Halides of Alkali Earth Metals

Sulphates of Alkali Earth Metals

Magnesium Sulphate,Epsom Salt MgSO4.7H2O

Oxides of Magnesium and Calcium

Magnesia

Calcium oxide, Quick lime

Hydroxides of Mg & Ca

Magnesium Hydroxide

Calcium Hydroxide, Slaked lime

Calcium Carbonate

Magnesium Carbonate

Bicarbonates of Mg & Ca

Halides of Mg & Ca

Plaster of Paris

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General Characteristics of Compounds of the Alkaline Earth Metals
 

Oxides of Alkali Earth Metals

The oxides of alkali earth metals (MO) are obtained either by heating the metals in oxygen or by thermal decomposition of their carbonates.            

2M + O2  2MO   ( M = Be, Mg, Ca)       

MCO3  MO + CO2   ( M = Be, Mg, Ca, Sr, Ba)

Expect BeO all other oxides are extremely stable ionic solids due to their high lattice energies.

These have high melting point, have very low vapour pressure, are very good conducts of heat, are chemically inert and act as electrical insulators. Therefore, these oxides are used for lining furnaces and hence used as refractory materials.

Due to small size of beryllium ion, BeO is covalent but still has high melting point because of its polymeric nature.
 

Hydroxides of Alkali Earth Metals

The hydroxides of Ca, Sr & Ba are obtained either by treating the metal with cold water or by reacting the corresponding oxides with water. The reaction of these oxides with H2O is also sometimes called as slaking.

M + 2H2O  →  M (OH)2 + H2 ( M = Ca, Sr, Ba)

MO + H2O → M (OH)2 (M = Ca, Sr, Ba)                            

Be(OH)2 and Mg(OH)2 being insoluble are obtained from suitable metal ion solutions by precipitation with OH- ions.

BeCI2 + 2NaOH → Be (OH)2 ↓ + 2NaCI               

MgSO4 + 2NaOH → Mg (OH)2 ↓ + Na2SO4