Acids, Bases and Salts

Generally, salts are obtained by treating an acid with a base. Salts consist of both positive ions or 'cations', and negative ions or 'anions'. The cations are called basic radicals and are mostly obtained from metallic ions (ammonium ion being one exception), while the anions are called acidic radicals and are obtained from acids.

Salt is a compound, which on dissociation in water yields positive ions other than a hydrogen ion or hydronium ion, and a negative ion other than hydroxyl ion.

Family of Salts
Salts can be classified into the following types:

Normal or Neutral Salts
A salt that does not contain any replaceable hydrogen ions is a normal salt. It is obtained by replacing all the hydrogen ions of an acid by metal ions or ammonium ions. 

Examples: NaCl, Na₂SO₄, Na₃PO₄, NH₄Cl, K₂CO₃, CuSO₄ etc.

Bisalts or Acid Salts
A bisalt or an acid salt contains replaceable hydrogen ions in association with the acidic radicals. It is obtained by the incomplete replacement of hydrogen ions by metal ions or ammonium ions.

Examples: NaHCO₃, NaH₂PO₄ and Na₂HPO₄.

Since such salts also contain hydrogen ion, the term 'bi' or acid can be substituted by hydrogen, e.g. sodium bicarbonate or sodium acid carbonate is also called sodium hydrogen carbonate.

When bisalts or acid salts dissociate in water, they yield hydrogen or hydronium ions.

i) An acid salt reacts with bases to form salt and water only.

ii)

iii) They react with carbonates to yield carbon dioxide.

Remember

Some Common Acid Salts NaHCO3, NaHSO3, NaHSO4, Na2HPO4, Ca(HCO3)2, Ca(HSO4)2, KHCO3, KHSO3, KHSO4, NaH2PO4and Mg(HCO3)2

Basic Salts
A basic salt is formed when there is a higher proportion of the base in the reaction between an acid with a base, than is necessary for the formation of a normal salt.

Example:

Basic copper carbonate CuCO₃.Cu(OH)₂

Basic lead carbonate (white lead) PbCO₃.Pb(OH)₂

Double Salts
Such salts are formed by the intimate association of two simple salts, when crystallized from a solution of a mixture of the two.

Some Common Double Salts
Potassium alum
Ammonium alum
Ferric ammonium alum
Potassium chromium alum

Mixed Salts
Salts that contain more than one acid radical or basic radical are called as mixed salts.

Some Common Mixed Salts
Potassium calcium phosphate
Bleaching powder
Sodium potassium carbonate
Sodium potassium sulphate

Complex Salts
Salts that dissociate in water to give one simple ion and one complex ion are called complex salts.