SALTS

A substance formed by neutralization of an acid with a base is called a salt. For e.g.

Ca(OH)2 + H2SO4→ CaSO4 + H20

2Cu(OH)2 + 4HNO3→ 2Cu(NO3)2 + 2H2O

NaOH + HCI → NaCl + H2O

CLASSIFICATION OF SALTS:

Salts have been classified on the basis of chemical formulae as well as pH values.

(a) Classification Based on Chemical Formulae

(i) Normal salts: A normal salt is the one which does not contain any ionisable hydrogen atom or hydroxyl group. This means that it has been formed by the complete neutralisation of an acid by a base.

For e.g. NaCI, KCI, NaNO3, K2SO4 etc.

(ii) Acidic salts: An acidic salt is that which contains some replaceable hydrogen atoms. This means that the neutralisation of acid by the base is not complete. For example, sodium hydrogen sulphate (NaHSO4), sodium hydrogen carbonate (NaHCO3) etc.

(iii) Basic salts: A basic salt is that which contains some replaceable hydroxyl groups. This means that the neutralisation of base by the acid is not complete. For example, basic lead nitrate Pb(OH)NO3. Basic lead chloride, Pb(OH)CI etc.

 Classification Based on pH Values:

Salts are formed by the reaction between acids and bases. Depending upon the ^nature of the acids and bases or upon the pH values, the salt solutions are of three types.

(i) Neutral salt solutions: Salt solutions of strong acids and strong bases are neutral and have pH equal to 7. They do not change the colour of litmus solution.

For e.g.: NaCI, KCI, NaNO3, Na2SO4 etc.

(ii) Acidic salt solutions: Salt solutions of strong acids and weak oases are of acidic nature and have pH less than 7. They change the colour of blue litmus to red. For e.g. (NH4)2SO4,NH4CI etc. In both these salts, the base NH4OH is weak while the acids H2SO4 and HCI are strong.

(iii) Basic salt solutions: Salt solutions of strong bases and weak acids are of basic nature and have pH more than 7. They change the colour of red litmus solution to blue. For e.g. Na2CO3, K3PO4 etc.

In both the salts, bases NaOH and KOH are strong while the acids H2CO3 and H3PO4 are weak.

USES OF SALT

  • As a table salt.
  •  In the manufacture of butter and cheese.
  •  In the manufacturing of washing soda and baking soda.
  •  For the preparation of sodium hydroxide by electrolysis of brine.
  • Rock salt is spread on ice to melt it in cold countries.