Class Seven science Chapter 5 Acid-base and salt

Chapter 5 Acid-base and salt

Neutralisation in Everyday Life

There are many uses of neutralization reactions in everyday life.


• Our stomach releases hydrochloric acid which helps in the digestion of food. Sometimes our stomach produces more hydrochloric acid than required which causes indigestion. This condition can be painful and causes pain in the stomach.

• To get relief from such symptoms, a medicine made of milk of magnesia (a base) is taken which contains magnesium hydroxide and neutralizes the effect of excessive hydrochloric acid.

Ant sting

• Ant sting or bee sting contains formic acid. Bee or ant injects formic acid into our skin while biting that causes pain at the place of bite.

• To neutralize the effect of acid injected by bee or ant we rub baking soda or zinc carbonate over the skin.

Soil treatment

• Soil becomes acidic or basic due to excessive use of chemical fertilizers. Plants do not grow properly on such soil.

• The bases like Slaked lime or quick lime are used to treat soil which is too acidic. These bases neutralize the acidic nature of the soil.

• On the other hand, organic matter is used to treat soil which is too basic. Organic matter produces an acid that helps in neutralizing the basic nature of the soil.

Factory waste

• The waste materials of most of the factories are acidic. These waste materials kill the aquatic organisms and pollute the water when flushed into the water bodies like rivers, ponds etc.

• Therefore, the basic substances are used to neutralize the acid present in these waste materials before being flushed in the river.

Through a pH chart, we can estimate the strength of an acid or base.

Reading 7 on a pH chart shows that a substance is neutral

whereas substances with pH value less than 7 are acidic and more

than 7 are basic in nature. Check the table below and find out the pH value with the reference to the colour.

Important Terms

Acids: A substance that reacts with a base to form salt and water is called acid.

Bases: A substance that can neutralize an acid to form salt and water is called the base.

Neutral: Substances that are neither acidic nor basic are called neutral.

Indicators: Solutions of substances that show different colour in acidic, basic and neutral solutions are called indicators.

Litmus: It is extracted from lichens. It is available in the form of strips of paper or in the form of a solution. Acid turns blue litmus red. Bases turn red litmus blue.

Turmeric: It is yellow in colour and remains as such both in acidic and neutral solutions. Turmeric paper turns into red or deep brown when it is dipped into a basic solution.

China rose: China rose indicator is a light pink coloured solution that is extracted from the red flowers of China rose plant with water.

Phenolphthalein: It is an acid-base indicator. It is colourless in acidic solutions but turns pink in alkali solutions.

Neutralization: It is the reaction between an acid and a base which results in the formation of salt and water.

Indigestion: Too much acid in the stomach causes indigestion. It is neutralized by taking an antacid like milk of magnesia.

Ant sting: Ant sting or bee sting contains formic acid. Bee or ant injects formic acid into our skin while biting that causes pain at the place of bite. The effect is neutralized by rubbing moist baking

soda or calamine at the place of bite.

Soil treatment: When the soil is too acidic, it is neutralized by treating with quicklime (calcium oxide) or slaked lime (calcium hydroxide) and organic matter is used to treat basic soil.