Preparation And Properties Of Bases

CLASSIFICATION BASED ON STRENGTH
Strong alkali :-    
The alkalis which almost completely dissociates in an aqueous solution to produce high concentration of hydroxyl \( (OH^ - ) \) ions are called as strong alkalis.

                                     \( KOH \rightleftharpoons K^ + + OH^ - \)        

Weak alkali :-
The alkalis which undergo partial dissociation in an aqueous solution so as to produce low concentration of hydroxyl ions are called weak alkalis.
            
            \( NH_4 OH \rightleftharpoons NH_4 ^ + + OH^ - \)

        Ex: Ca(OH)₂, Mg(OH)₂    

Concentrated alkali :-
An alkali solution having a relatively high percentage of alkali in its aqeous solution is called concentrated alkali.

Dilute alkali :-
    An alkali solution having relatively less percentage of alkali in its aqeous solution is called dilute alkali.

ACIDITY OF A BASE / ALKALI

Acidity of an alkali :
The number of hydroxyl ions \( (OH^ - ) \) furnished by one molecule of an alkali on complete dissociation in water is called acidity of an alkali.

Acidity of a base :
 As most of the bases are insoluble in water, therefore, their acidity cannot be determined by dissolving in water. So, The number of hydronium ion H⁺ (aq) of an acid, which will react completely with one molecule of a base to form salt and water as the only products is called acidity of a base.

a) Mono acidic alkali / base:
An alkali which furnishes one hydroxyl ion \( OH^ - \) per molecule or a base whose one molecule reacts with one hydronium ion \( \left[ {H_{(aq)}^ + } \right] \) completely to form salt and water as the only
products is called mono acidic alkali / base.
        Ex :    LiOH, NaOH

b) Diacidic alkali / base:
An alkali which furnishes two hydroxyl ion \( (OH^ - ) \)  per molecule or a base whose one molecule reacts with two hydronium ions \( \left[ {H_{(aq)}^ + } \right] \) completely to form salt and water as the only products is called diacidic alkali / base.
        Ex :  Ca(OH)₂ ,Mg(OH)₂ ;        base : CU(OH)₂ 

C) Triacidic bases:
The base whose one molecule reacts with three hydronium ions \( \left[ {H_{(aq)}^ + } \right] \) completely to form salt and water as the only products is called tribasic acid.
        Ex :    Al(OH)₃, Fe(OH)₃