Acids, Bases and Salts Part - 6 | Class 10th

SALTS:

A Salt is an ionic compound which is made up of two groups of oppositely charged ions. The ion with a positive charge is called a cation, and the one with a negative charge is called an anion.

  Ø  Classification of salts

·           Normal salts: A normal salt is obtained by complete neutralization of an acid by a base.

NaOH + HCl → NaCl + H2O

·           Acid salts: Acid salts are derived by the partial replacement of hydrogen ions of an acid by a metal. When a calculated amount of a base is added to a polybasic acid, acid salt is obtained, as follows.

NaOH + H₂SO₄ → NaHSO₄ + H₂O

·           Basic salts: Basic salts are formed by the partial replacement of hydroxide ions of a diacidic or triacidic base by an acid radical. A basic salt may further reacts with an acid to give a normal salt.

Pb(OH)₂ + HCl → Pb(OH)Cl + H2O

                     Diacidic base                   Basic salt

  Ø  Family of Salts: Salts can be classified into the following types:  Normal or Neutral Salts - A salt that is formed by the complete replacement of the replaceable hydrogen ions of an acid by a metal ion or ammonium ion is called a normal salt.  Examples:

Neutral Salts: Strong Acid + Strong base pH value is 7. Examples: NaCl, CaSO₄

Acidic Salts: Strong Acid + weak base pH value is less than 7. Examples: NH₄Cl, NH₄NO₃

Basic Salts: Strong base + Weak acid pH value is more than 7. Examples: Na₂CO_3, CH₃COONa. 

  Ø  Neutralisation: The reaction between an acid and a base to form salt and water is called a neutralisation reaction.

Acid   +   Base   →     Salt   +    Water

v Hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water. 

HCl        +     NaOH    →      NaCl        +           H₂O

v Sodium sulphate and water are formed when sulphuric acid reacts with sodium hydroxide (a base).

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

v Calcium chloride is formed along with water when hydrochloric acid reacts with calcium hydroxide (a base).

2HCl + Ca(OH)₂ → CaCl₂ + 2H₂O

Ø  Reaction of Acid with Metal Oxides: Metal oxides are basic in nature. Thus, when an acid reacts with a metal oxide both neutralize each other. In this reaction, respective salt and water are formed.

Acid + Metal Oxide → Salt + Water

v Sulphuric acid reacts with zinc oxide, zinc sulphate and water are formed.

H₂SO₄ + ZnO → ZnCl₂ + H₂O

v Copper oxide (II), a black metal oxide reacts with dilute hydrochloric acid to form a blue-green coloured copper chloride (II) solution.

CuO        +        2HCl    →     CuCl₂(aq)     +     H₂O