Class 7 Science

Acid Base Salt


When a solution of acid is mixed with the solution of base, both of them neutralize each other and a third substance (called salt) is formed. Such phenomenon is called neutralization or neutralization reaction. The solution formed because of mixing of solution of acid and base is neither acidic nor basic in nature. Such solution is known as neutral solution.

Acid + Base → Salt + Water

Salt formed because of neutralization reaction may be acidic or basic in nature. Acidic or Basic nature of salt depends upon the strength of acid and base. In neutralization reaction heat is evolved. Reactions in which heat is evolved are known as exothermic reactions. Thus, neutralization reaction is an exothermic reaction.

Example: Sodium hydroxide is a base and hydrochloric acid is an acid. When solution of sodium hydroxide is mixed with the solution of hydrochloric acid, both neutralize each other and common salt (Sodium chloride) is formed. Since, it is an exothermic reaction, so reaction mixture becomes slightly hot. The reaction involved in this can be written as follows:

HCl + NaOH → NaCl + H2O

Sodium chloride is the chemical name of common salt which is used in household.

Neutralization Reaction in Everyday Life

There are many uses of neutralization reaction in everyday life. Some examples are as follows:


Our stomach releases hydrochloric acid to kill bacteria (if any) present in food. Hydrochloric acid released in our stomach also helps in the digestion of food. Sometime our stomach produces more hydrochloric acid than required. Production of excess hydrochloric acid in the stomach manifests as indigestion. This condition can be painful and causes pain in abdomen and burning sensation in chest.

To get rid of such symptoms, a medicine made of Milk of magnesia (a base) is taken orally. Milk of magnesia, being a base neutralizes the hydrochloric acid and gives relief from indigestion.

Ant Sting

Ant sting or bee sting contains methanoic acid. Methanoic acid is also known as formic acid. Bee or ant injects formic acid into our skin, while biting. Injection of acid by ant or bee results in pain at the place of bite.

Rubbing baking soda over the skin gives relief from pain due to ant or bee sting. Baking soda, which is a base, neutralizes the effect of acid injected by bee or ant. Another base, such as zinc carbonate (Calamite solution) is also used in case of ant or bee sting.

Soil Treatment

Sometimes soil becomes acidic or basic due to excess use of fertilizers or wrong method of harvesting. Acidic or basic nature of soil affects the yield as plants do not grow properly on such soil.

Acidic soil is treated with slaked lime or quick lime. Slaked lime (Calcium hydroxide) and quick lime (Calcium oxide) are bases. Use of slaked lime or quick lime neutralizes the acidic nature of soil.

Basic soil is treated with organic matter. Organic matter releases acid and neutralizes the basic nature of soil.

Factory Waste

Wastes of most of the factories are acidic. If such acidic wastes are flushed into rivers, acid present in them kills the aquatic organisms and pollutes the water. Thus, factory wastes are treated with basic substances to neutralize the acid present in them before being flushed in the river.

Important Points: