Online Notes on Chapter=2 ( Acids, Bases and Salts) Part 2

This is Online Notes on Chapter=2 ( Acids, Bases and Salts)  Part 2 for preparation of CBSE BOARD Examination, NTSE etc.





Acid or Base in Water Solution

• Acids produce H⁺  ions in presence of water.

• H⁺ ions cannot exist alone, they exist as H₂O⁺ (hydronium ions).

H⁺ + H₂O → H₃O⁺

HCl + H₂O → H₃O⁺ + Cl−

Bases when dissolved in water gives OH^- ions.

NaOH   ==H₂O=>  Na⁺ + OH^-

Mg(OH)₂   ==H₂O==> Mg²⁺ +  2OH^-

• Bases soluble in water are called alkali.

• While diluting acids, it is recommended that the acid should be added to water
and not water to acid because the process of dissolving an acid or a base in

water is highly exothermic.

Strength of Acid and Base


Strength of acid or base can be estimated using universal indicator.

Universal indicator : is a mixture of several indicators. It shows different colours at different concentrations of H⁺ ions in the solution.

pH Scale : A scale for measuring H⁺ ion concentration in a solution . p in pH stands for ‘potenz’ a German word which means power.

pH = 7 → neutral solution

pH less than 7 → acidic solution


pH more than 7 → basic solution

pH of Salts :

(i) Strong Acid + Strong Base → Neutral Salt : pH = 7

(ii) Salt of strong acid + Weak base → Acidic salt : pH < 7


(iii)Salt of strong base + Weak acid → Basic salt : pH > 7

1. Sodium Hydroxide (NaOH) : When electricity is passed through an aqueous
solution of NaCl (brine), it decompose to form NaOH. (Chlor-alkali process)

2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂

At anode : Cl₂ gas

At cathode : H₂ gas

Near cathode : NaOH solution is formed.

Uses :
H₂ : Fuels, margarine

Cl₂ : Water treatment, PVC, CFC’s

HCl : Cleaning steels, medicines

NaOH : Degreasing metals, soaps and paper making

Cl₂ + NaOH → Bleach : Household bleaches, bleaching fabrics

2. Bleaching Powder (CaOCl₂) : It is produced by the action of chlorine on dry
slaked lime.

Cl₂ + Ca(OH)₂ → CaOCl₂ + H₂O

Uses :
(a) Bleaching cotton and linen in textile industry.

(b) Bleaching wood pulp in paper factories.

(c) Oxidizing agent in chemical industries.

(d) Disinfecting drinking water.

3. Baking Soda (Sodium Hydrogen Carbonate) (NaHCO₃) :

NaCl + H₂O + CO₂ + NH₃→ NH₄Cl + NaHCO₃

Baking soda
• It is mild non-corrosive base.

• When it is heated during cooking :

2NaHCO₃   ==Heat=> Na2CO3 + H2O + CO2

Uses :
(a) For making baking powder (mixture of baking soda and tartaric acid). When
baking powder is heated or mixed with water, CO₂ is produced which causes
bread and cake to rise making them soft and spongy.

(b) An ingredient in antacid.

(c) Used in soda acids, fire extinguishers.


4. Washing Soda (Na₂CO₃.10H₂O) : Recrystallization of sodium carbonate gives

washing soda. It is a basic salt.

Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O

Uses :
(a) In glass, soap and paper industry.
(b) Manufacture of borax.
(c) Cleaning agent for domestic purposes.
(d) For removing permanent hardness of water.


5. Plaster of Paris (Calcium sulphate hemihydrates) (CaSO₄.½H₂O) : On heating gypsum (CaSO₄.2H₂O) at 373K, it loses water molecules and becomes Plaster of Paris (POP).

It is a white powder and on mixing with water it changes to gypsum.

CaSO₄.½H₂O + 1½H₂O → CaSO₄.2H₂O

Uses :

(a) Doctors use POP for supporting fractured bones.

(b) For making toys, material for decoration.

(c) For making surfaces smooth.

Water of Crystallization : It is a fixed number of water molecules present in one formula unit of a salt.

E.g., CuSO₄.5H₂O has 5 water molecules.

Na₂CO₃.10H₂O has 10 water molecules.


CaSO₄.2H₂O has 2 water molecules.