Salts are of the following types

(i) Simple salts : In case the acid and base neutralise completely the salt formed is a normal salt. Normal salts are produced by the replacement of all replaceable hydrogen(s) present in the molecule of an acid by metal or `NH_4^+` group.

`H_2CO_3 + 2NaOH -> Na_2CO_3 + H_2O`

(ii) Acidic Salts : If a polybasic acid (Example, `H_2SO_4`, `H_3PO_4`, `H_2SO_3` etc.) is neutralised partly by a base, the salt formed is acidic. In other words such salts are produced by the replacement of only a part of the acidic hydrogen of the polybasic acids by a metal.

`H_2CO_3 + NaOH -> NaHCO_3 + H_2O`

(iii) Basic salts : This type of salts are formed by incomplete neutralization of a base with an acid or by partial replacement of hydroxyl radicals of a diacidic or triacidic base with an acid radical. Examples: `Cu(OH)NO_3` - Basic copper nitrate.

`[Cu(OH)_2 + HNO_3 -> Cu(OH)NO_3 + H_2O]`

(iv) Double salts : Such a salt is formed by mixing saturated solution of two simple salts followed by crystallisation of the saturated solution. Example :

`FeSO_4 (NH_4)_2SO_4. 6H_2O` (Mohr's salt) is a mixture of `FeSO_4` (Simple salt) and `(NH_4)_2SO_4` (Simple salt), Potash alum `K_2SO_4 * Al_2 (SO_4)_3 * 24 H_2O`, Carnallite `KCl * MgCl_2 * 6H_2O`

(v) Mixed salts : There is no general method for the formation of this type of salt. Examples: Sodium potassium sulphate `NaKSO_4` (two basic radicals, `Na^+`, `K^+`) e.g. `NaKSO_4`, `Ca (OCl) Cl`, `Mg(NH_4)_2 PO_4 ` etc.

(vi) . Complex salts : Such a salt is formed by mixing saturated solution of simple salts followed by crystallisation of the solution similar to double salts. e.g. when ferrous sulphate solution and potassium cyanide solution are mixed together, `K_4 [Fe(CN)_6]` is formed.

`FeSO_4 +6KCN → K_4 [Fe (CN)_6 ] +K_2SO_4.`

(i) When a salt of strong base and weak acid or weak base and strong acid is dissolved in water, it reacts with water to give back the original acid and base from which the salt was formed. This process is known as salt hydrolysis.

(ii) Hydrolysis is the reverse process of neutralisation reaction.

(iii) Only salt of weak acid + strong base, weak base + strong acid undergo hydrolysis.

(iv) The phenomena in which cation or anion of both of a salt react with water to produce acidic or alkaline solution is known as hydrolysis

`undersettext(salt)(CA) undersettext(hydrolysis) oversettext(HOH) → undersettext(Cation)(C^+)+ undersettext(Anion) (A^-)`

(v) The interaction of anion of a salt with water to give alkaline solution is called anionic hydrolysis.

`undersettext(Anion of salt) (A^-) +H_2O ⇌ undersettext(Weak acid) (HA) + OH^-`

(vi) The interaction of cation of a salt with water to give acidic solution is called cationic hydrolysis.

`undersettext(Cation)(C^+) +2H_2O ⇌ undersettext(Weak base) (COH) + undersettext(Hydronium ion) (H_3O^+)`

(vii) The aqueous solution of salt of strong acid and strong base is neutral e.g. `NaCl , KCl , Na_2SO_4` etc .

(viii) The aqueous solution of salt of strong acid and weak base is acidic e.g. `FeCl_3 , NH_4Cl , (NH_4)_2SO_4`. etc.

(ix) The aqueous solution of salt of weak acid and strong base is basic e.g. `CH_3COONa , Na_2CO_3` etc.