Chemistry

लवणों के प्रकार :लवणो के भिन्न प्रकार सामान्य लवण, अम्लीय लवण, क्षारीय लवण तथा द्विकलवण है
3. Basic salt : When a polyacidic base reacts with lesser amount of acid than is necessary for complete neutralization, the salt produced contain hydroxyl group(s) (OH) also. Such a salt is called a basic salt.
EXAMPLES : 1 mole of Pb(OH)₂ requires 2 moles of HCl for complete neutralization. But when 1 mole of Pb(OH)₂ is made to react with 1 mole of HCl, some Pb(OH)₂ is left unreacted. The salt produced is not PbCl₂ but Pb(OH)Cl.

Similarly, when one mole of Bi(OH)₃ is reacted with 1 mole of HNO₃, the salt Bi(OH)₂NO₃ is formed.
Bi(OH)₃ + HNO₃ → Bi(OH)₂NO₃ + H₂O
Salts like Pb(OH)Cl and Bi(OH)₂NO₃ contain the OH group. These salts are called basic salts, because they can further react with the acids to form H₂O and the corresponding normal salts.
Pb(OH)Cl + HCl → PbCl₂ + H₂O
Bi(OH)₂NO₃ + HNO₃ + Bi(OH)(NO₃)₂ + H₂O
Bi(OH)(NO₃)₂ + HNO₃ → Bi(NO₃)₃ + H₂O
Thus, a basic salt is formed when a poly acidic base reacts with a lesser amount of an acid than is necessary for the formation of a normal salt.
4. Double salt : In a double salt, there are two different negative ions and/or positive ions. For example, the mineral dolomite, CaCO₃ • MgCO₃ contains both Ca²⁺and Mg²⁺ ions. Hence, it is a double salt. Potash alum, K₂SO₄ • Al₂(SO₄)₃ • 24H₂O, also is a double salt.
Double salts exist only in the solid state. When dissolved in water, they break up into a mixture of two separate salts. For example, when potash alum is dissolved in water, it breaks up as follows.