LESSON 4

SALTS

A salt is the substance formed when either all or part of ionisable hydrogen ions of an acid is replaced by a metallic ion or ammonium ion. A salt is formed when an acid reacts with base.

TYPES OF SALTS

1. Normal salts

Normal salt is a salt formed when all the ionisable hydrogen ions of an acid are replaced by a metallic ion or ammonium ion.

 Examples of normal salts

  • Sodium sulphate
  • Potassium nitrate
  • Calcium chloride

In general normal salts include chlorides, sulphates, sulphites, nitrates, phosphates and carbonates of metals and ammonium radical.

2. Acid salts

Acid salt is a salt formed when ionisable hydrogen ions of an acid are partially replaced by a metallic ion or ammonium ion.

Examples

  • Potassium hydrogen carbonate (KHCO3)
  • Sodium hydrogen sulphate (NaHSO4)
  • Sodium hydrogen sulphite (NaHSO3)

In general acid salts include:-

Hydrogen carbonates, hydrogen phosphates of metals and ammonium radical.

Acid salts are formed when dibasic or tribasic acids are reacted with metal ions or ammonium ions.

3. Basic salts.

A basic salt is a compound of the normal salt and a base from which its derived e.g basic zinc chloride, Zn(OH)Cl, basic magnesium chloride, Mg(OH)Cl.

4. Double salts

A double salt is a combination of two normal salts. They consist of two different positive ions and one common negative ion. Most double salts contain water of crystallization loosely attached to the cations in the salt.

Examples of double salts.

  • Potassium aluminium sulphate, K2SO4.Al2(SO4)3.24H2O  Potassium magnesium chloride, KCl.MgCl2.6H2
  • Ferrous ammonium sulphate,(NH4)2SO4.FeSO4.6H2

HYDRATED SALTS

Hydrated salts are salts which contain water of crystallization.The water molecules are combined with the  crystals.The number of water molecules varies depending on the salt.A crystalline compound containing water is hydrated and the water is sometimes called water of hydration.

Examples of hydrated salts.

  • Copper sulphate crystals, CuSO4.5H2O.
  • Iron(II) sulphate crystals,FeSO4.7H2O.
  • Magnesium sulphate crystals, MgSO4.7H2O.
  • Sodium sulphate crystals, Na2SO4.10 H2O
  • Sodium carbonate crystals,Na2CO3.10 H2O

 An hydrous salts are salts which do not contain water of crystallization.Anhydrous means without water’.

Examples of anhydrous salts

  • Sodium chloride
  • Potassium chloride
  • Potassium nitrate
  • Ammonium chloride Potassium manganate