5
Question
(a) Describe the importance of pH in everyday life. Illustrate your answer with examples.
(b) A farmer has found that the pH of soil in his fields is 4.2. Name any two chemical materials which he can mix with the soil to adjust its pH. Give reason for your choice.
(c) Why are detergents also called 'soap-less soaps'? Give the various advantages of detergents over soaps.
(d) A person put some universal indicator paper onto wet soap. The pH is found to be 8. What does this tell you about soap?
(b) A farmer has found that the pH of soil in his fields is 4.2. Name any two chemical materials which he can mix with the soil to adjust its pH. Give reason for your choice.
(c) Why are detergents also called 'soap-less soaps'? Give the various advantages of detergents over soaps.
(d) A person put some universal indicator paper onto wet soap. The pH is found to be 8. What does this tell you about soap?
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Solution
(a) pH has great importance in our daily life:
(i) pH and plants:
Plants require a specific pH for growth. It cannot grow in too acidic or too basic soils. If soil is too acidic then its pH can be increased by adding lime:
And on the other hand, if the soil is too alkaline then its pH can be decreased by adding gypsum.
(ii) pH and blood or digestive system:
The pH of blood is tightly regulated in the range of 7.2-7.4 and medium in our stomach is highly acidic (pH = 1.2). Sometimes stomach produces too much hydrochloric acid which causes irritation or pain.
(iii) pH and skin:
The acidic pH of the skin prevents colonization by bacteria. Thus, it acts as a defense mechanism against infection.
(b) As the acidity of the soil increases, it becomes improper for cultivation. To reduce the acidity of the soil, the farmer will have to add quick lime or slaked lime his fields.
(c) Soaps are sodium or potassium salts of fatty acids, however, detergents are not salts but are simply surface active chemicals showing soap-like properties, hence they are called as soapless detergents.
Advantage of detergents over soap: Detergents are often preferred over soap as they are more effective at cleaning and have a wider range of applications. They can also be used in hard water.
(d) pH of the soap was found to be 8, which means the soap is of basic nature. Universal indicator show solutions with pH greater than 7 are bases.
(i) pH and plants:
Plants require a specific pH for growth. It cannot grow in too acidic or too basic soils. If soil is too acidic then its pH can be increased by adding lime:
And on the other hand, if the soil is too alkaline then its pH can be decreased by adding gypsum.
(ii) pH and blood or digestive system:
The pH of blood is tightly regulated in the range of 7.2-7.4 and medium in our stomach is highly acidic (pH = 1.2). Sometimes stomach produces too much hydrochloric acid which causes irritation or pain.
(iii) pH and skin:
The acidic pH of the skin prevents colonization by bacteria. Thus, it acts as a defense mechanism against infection.
(b) As the acidity of the soil increases, it becomes improper for cultivation. To reduce the acidity of the soil, the farmer will have to add quick lime or slaked lime his fields.
(c) Soaps are sodium or potassium salts of fatty acids, however, detergents are not salts but are simply surface active chemicals showing soap-like properties, hence they are called as soapless detergents.
Advantage of detergents over soap: Detergents are often preferred over soap as they are more effective at cleaning and have a wider range of applications. They can also be used in hard water.
(d) pH of the soap was found to be 8, which means the soap is of basic nature. Universal indicator show solutions with pH greater than 7 are bases.
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