Substances have either acidic, basic or neutral properties.
Acids are sour to the taste, and include substances like
curd, vinegar, lemon, orange juice, etc.
Bases are bitter to the taste and slippery to the touch,
and include substances like baking soda milk of magnesia, etc.
When an acid is mixed with a base in the right proportion, they
neutralise the effect of each other. That means the acidic nature of
the acid and the basic nature of the base are destroyed. This reaction
is called neutralisation. The neutralisation reaction between
an acid and a base can be identified by an indicator. For
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 colour slowly fades to pale pink and
then colourless. This change in colour indicates
The neutralisation reaction between hydrochloric acid and
sodium hydroxide can be written as
Hydrochloric acid +Sodium hydroxide → Sodium chloride +
Water Heat is also produced during a neutralisation reaction.
Neutralisation is useful in our daily life.
Acidity caused by indigestion can be reduced by
neutralising the hydrochloric acid in the stomach by a base, like milk
An ant’s sting gives a lot of pain due to formic
acid. It can be neutralised by applying calamine lotion, or
rubbing with baking soda.
Excessive use of chemical fertilisers makes soil acidic.
Neutralising the soil with a base like quick lime, which is
calcium oxide, or slaked lime, which is calcium hydroxide, will
make this soil suitable for plants.