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Neutralisation - Lesson Summary

The reaction of an acid with a base to give salt, water and heat is called neutralisation. 
Example: Hydrochloric Acid + Sodium Hydroxide → Sodium Chloride + Water + Heat
                HCl + NaOH → NaCl + H2O + Heat
The heat evolved in the neutralisation reaction raises the temperature of the reaction mixture.
Example: During the mixing of dilute sulphuric acid with potassium hydroxide, the test tube heats up.

The neutralisation reaction between an acid and a base can be identified by an indicator.
Example: For the reaction between hydrochloric acid and sodium hydroxide, phenolphthalein is added as an indicator. Phenolphthalein is pink in sodium hydroxide. When hydrochloric acid is added to it, the color slowly fades to pale pink and then colorless. This change in color indicates neutralisation.

Classification of simple salts
Salts can be classified into acidic, basic and neutral salts.
When a strong acid reacts with a weak base acidic salts are formed.
Example: Ammonium chloride.
When a strong base reacts with a weak acid basic salts are formed.
Example: Sodium acetate.
When a strong acid reacts with a strong base neutral salts are formed.
Example: NaCl, KNO3, CaBr2.

Properties of salts
Melting and boiling points
Most of the salts are solids. And they have high melting and boiling points.

Solubility in water
Generally salts are soluble in water.
Examples:  Sodium chloride, Potassium sulphate, Ammonium carbonate and aluminium nitrate are soluble in water.
Silver chloride, lead chloride, copper carbonate, etc., are the examples for water insoluble salts.

Water of crystallization
Some salts have a fixed number of water molecules as an essential part of their crystal. These water molecules which form the part of the crystal are called water of crystallization and such salts are called hydrated salts. These water molecules are responsible for the crystal its shape and color of some crystals. In general they exist as dry in pure form. These salts on heating lose water molecules in them and forms anhydrous salts.
For example, in your laboratory, the blue coloured copper sulphate is copper sulphate penta hydrate. When heated, this salt loses its water molecules as a result the copper sulphate crystal lose its shape and color and changed to a powdery substance.
CuSO4.5H2O (On heating) → CuSO4 + 5H2O

Neutralisation in Daily Life
Neutralisation in Digestion
The stomach contains hydrochloric acid, which helps in the digestion of food. If  this acid is produced in excess, it causes indigestion, which is painful.
An antacid such as milk of magnesia neutralises the excessive acid in the stomach, and provides relief from the pain due to indigestion.

Neutralisation- Ant Sting
Ant sting contains formic acid. When an ant bites, it injects this formic acid into the skin. This causes pain.
It can be neutralised by rubbing the ant bite with moist baking soda, which contains sodium hydrogen carbonate (NaHCO3), or with a solution of calamine, which contains zinc carbonate (ZnCO3).

Neutralisation - Acidic Soil
Excessive use of fertilisers makes soil acidic. As a result, plants cannot grow properly, and the yield decreases. Adding a base like quick lime, (calcium oxide) or slaked lime (calcium hydroxide) neutralises the soil and makes it suitable for plants.

Similarly, when soil is basic in nature, organic matter is added to release acid and make it neutral, and thus, suitable for plants.

Neutralisation - Factory Wastes
Factory waste contains acids. This waste must be treated with bases for neutralisation before it is released into a water source. Otherwise, it can cause damage to living organisms in the water source.

Uses of some salts

           Name of the salt   


 Sodium chloride -NaCl (Common salt)

To preserve pickles, fish and meat.
As a raw material for the manufacture of other compounds.

Sodium carbonate - Na2CO3.10H2O (Washing soda)

Used to manufacture of glass, cleansing agents, soap, glass and paper, sodium compounds like borax.

Sodium bicarbonate- NaHCO3 (Baking soda)

Used in bakery and antacids

Ammonium nitrate - NH4NO3

Used in fertilizers

Potash alum - K2SO4.Al2(SO4)3.24H2O

Used in purification of water

Silver nitrate

Used in photography


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