JEE Main & Advanced Chemistry Equilibrium / साम्यावस्था The Acid-Base Neutralisation And Salt

The reaction between an acid and a base to form salt and water is termed neutralisation

\[HC{{l}_{(aq.)}}+NaO{{H}_{(aq.)}}\] ? \[\underset{Salt}{\mathop{\underset{Sodium\,Chloride}{\mathop{NaC{{l}_{(aq.)}}}}\,}}\,+{{H}_{2}}{{O}_{(l)}}\]

The process of neutralisation does not produce the resulting solution always neutral; no doubt it involves the interaction of \[{{H}^{+}}\] and \[O{{H}^{-}}\]ions. The nature of the resulting solution depends on the particular acid and the particular base involved in the reaction.

Salts : Salts are regarded as compounds made up of positive and negative ions. The positive part comes from a base while negative part from an acid. Salts are ionic compounds. The salts can be classified into following classes,

(1) Simple salts : The salt formed by the interaction between acid and base, is termed as simple salt. These are of three types,

(i) Normal salts : the salts formed by the loss of all possible protons (replaceable hydrogen atoms as \[{{H}^{+}}\]) are called normal salts. Such a salt does not contain either replacable hydrogen or a hydroxyl group.

Examples :\[NaCl,\ NaN{{O}_{3}},{{K}_{2}}S{{O}_{4}},C{{a}_{3}}{{(P{{O}_{4}})}_{2}},N{{a}_{3}}B{{O}_{3}},\]  \[N{{a}_{2}}HP{{O}_{3}}\] (one \[H\] atom is not replaceable as \[{{H}_{3}}P{{O}_{2}}\] is a dibasic acid) \[Na{{H}_{2}}P{{O}_{2}}\] (both \[H\] atoms are not replaceable as \[{{H}_{3}}P{{O}_{2}}\] is a monobasic acid) etc.

(ii) Acidic salts : Salts formed by incomplete neutralisation of poly-basic acids are called acidic salts. Such salts still contain one or more replaceable hydrogen atoms. These salts when neutralised by bases form normal salts.

Examples : \[NaHC{{O}_{3}},NaHS{{O}_{4}},Na{{H}_{2}}P{{O}_{4}},N{{a}_{2}}HP{{O}_{4}}\], etc.

(iii) Basic salts : Salts formed by incomplete neutralisation of poly acidic bases are called basic salts. Such salts still contain one or more hydroxyl groups. These salts when neutralised by acids form normal salts.

Examples:\[Zn(OH)Cl,\ Mg(OH)Cl,\ Fe{{(OH)}_{2}}Cl,\ Bi{{(OH)}_{2}}Cl\]

(2) Double salts : The addition compounds formed by the combination of two simple salts are termed double salts. Such salts are stable in solid state only.

Examples : Ferrous ammonium sulphate, Potash alum and other alums.

(3) Complex salts : These are formed by combination of simple salts or molecular compounds. These are stable in solid state as well as in solutions.

\[\underset{\text{Simple}\ \text{salts}}{\mathop{FeS{{O}_{4}}+6KCN}}\,\to \underset{\text{Complex salt}}{\mathop{{{K}_{4}}[Fe{{(CN)}_{6}}]}}\,+{{K}_{2}}S{{O}_{4}}\]

(4) Mixed salts : The salt which furnishes more than one cation or more than one anion when dissolved in water is called a mixed salt.

 Examples :