Salts

SALTS DEFINITATION 

Acidic salt :A salt formed by the partial replacement of H+ ions of an acid from its molecule, with metal ions, is called acid salt.The acid salt on dissolving in water furnishes hydrogen ion (H+) and turns blue litmus solution red.

Examples of acid salts :

• Sodium hydrogen sulphate [NaHSO4]
• Sodium hydrogen carbonate [NaHCO3]
• Sodium hydrogen sulphite [NaHSO3]
• Potassium hydrogen sulphate [KHSO4]
• Potassium hydrogen carbonate [KHCO3]
• Potassium hydrogen sulphite [KHSO3]
• Calcium hydrogen carbonate [Ca(HCO3)2]
• Calcium hydrogen sulphate [Ca(HSO4)2]
• Magnesium hydrogen carbonate [Mg(HCO3)2]
• Magnesium hydrogen sulphate [Mg(HSO4)2]

Basic Salt :

A salt formed by the partial neutralisation of hydroxyl ions (OH–) of a base, by an acid is calledbasic salt.The basic salt on dissolving in water furnishes OH– ions and turns red litmus blue.

Examples of basic salts:

• Zinc hydroxy chloride [Zn(OH)Cl]

• Copper hydroxy chloride [Cu(OH)Cl]

• Interosting note: The red cabbage xtract (Obtained from red cabbage leaves) is a natural indicator.
• It is red in Colour: The red cabbage red cabbage extract remeains red in acidic solutions

Preparation of salts

By neutralization of an acid by base:

2NaOH + H2SO4 ⎯→ Na2SO4 + 2H2O

 By reaction of an acid with a metal:

Zn + dil. 2HCl → ZnCl2 + H2

Zn + dil. H2SO4 → ZnSO4 + H2

2Na + dil. 2HCl → 2NaCl + H2

(iii) By the action of acid an carbonates

Na2CO3 + dil. 2HCl → 2NaCl + H2O + CO2

ZnCO3 + dil. 2HCl → ZnCl2 + H2O + CO2

(iv) By the action of acid on metal oxides:

Na2O + dil. 2HCl → 2NaCl + H2O

ZnO + dil. H2SO4 → ZnSO4 + H2O

Properties of salts :

• Salts are mostly solids with high melting point and high boiling point.
• Salts are usually soluble in water.
• Solutions of salts in water conduct electricity.
• The crystals of some salts have some water molecules associated with them. These water molecules are known as water of crystallization. Such salts are called hydrated salts.The crystals which have lost their water of crystallization are called anhydrous.
•  Some salts have the tendency to absorb water from air and turn into a solution, such substances are called deliquescent. They are stored in air tight container and in dry places.
• Classification based on chemical formulae of salts:

(A) 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.

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

(B) Acidic salts: An acidic salt still contains some replaceable hydrogen atoms. This means that the neutralisation of acid by the base is not complete.

e.g. Sodium hydrogen sulphate (NaHSO4), sodium hydrogen carbonate (NaHCO3) etc.

(C) Basic salts: A basic salt still contains some replaceable hydroxyl groups. This means that the neutralisation of base by the acid is not complete.

e.g. Basic lead nitrate Pb(OH)NO3, basic lead chloride, Pb(OH)CI etc.