Acids, Bases and Salts

Acids are the chemical compounds that taste sour and turn blue litmus red. They are acidic in nature. Apple, lemon, orange, tomato, etc. are some examples of natural acids whereas curd, soft drinks, vinegar, etc. are some examples of man-made substances containing acids. Acids are classified on the basis of their strength, origin and concentration as strong and weak acids, organic and inorganic acids, dilute and concentrated acids respectively. Sulphuric acid, nitric acid and hydrochloric acid are the commonly known acids that are used in various fields. Bases are bitter in taste, soapy to touch and turn red litmus blue. They are basic in nature. Sodium hydroxide, potassium hydroxide, calcium hydroxide are some of the common examples of bases which are used in various fields. Soaps, detergents, baking powder, toothpaste are some bases that we use in our daily life. Neutral substances are those which are neither acidic nor basic. Pure water and sodium chloride solution are neutral substances. Indicators are the substances which are used to identify whether a substance is acid or base. The solutions of these substances show different colour in acidic, basic and neutral medium. They are natural as well as synthetic. Litmus, turmeric and extract of China rose petals are the natural indicators whereas phenolphthalein and methyl orange are some synthetic indicators. Salt is a compound formed by the reaction of an acid with a base. Salts are broadly classified into acidic salts, basic salts and normal salts. The reaction between an acid and a base is known as neutralisation. In neutralisation reaction, salt and water are produced with the evolution of heat. Neutralisation process holds great importance in everyday life like indigestion, treatment of ant bite, soil and factory waste treatment etc.

i 6. Applications of Neutralisation reaction-

i. Indigestion-Our stomach consists of hydrochloric acid which helps in digestion. The increased amount of this acid causes indigestion. Indigestion can be relieved by taking an antacid like milk of magnesia (magnesium hydroxide) which neutralises the effect of excessive acid.

ii. Ant sting-The ant sting contains formic acid. When an ant bites, it injects the acidic liquid into the skin. The effect of the sting can be neutralised by rubbing calamine (zinc carbonate) solution or moist baking soda.

iii. Soil treatment- The soil becomes acidic when chemical fertilisers are used in excess. Acidic or basic nature of soil prevents the growth of plants. When the soil is too acidic, it is treated with bases like quick lime (calcium hydroxide) or slaked lime (calcium hydroxide) and basic soil is neutralised by adding organic matter that releases acids.

iv. Factory wastes-The factory wastes contain acids. These acids will kill fish and other organisms if they are allowed to flow in the water bodies. Hence, these wastes are neutralised by adding basic substances.

7. Treasures- Acid rain is the rain containing excess of acids. The rain becomes acidic due to the presence of carbon dioxides, sulphur dioxide and nitrogen dioxide in air. These gases dissolve in raindrops to form carbonic acid, sulphuric acid and nitric acid. Acid rain can cause damage to historical monuments, buildings, plants and animals.

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