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?

Answer 1

Answer:

According to pH of soil, the soil is acidic in nature. A farmer should treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate) to neutralize the physical conditions of soil.

Answer 2

Explanation:

(a) Importance of pH:

1. The reaction of acid and base in digestive system.

2. The pH of the soil will determine the crops growing in it.

3. The acid from the sweets will decay the tooth.

(b) Adjusting pH of the soil:

From question, the soil is acidic. This soil is need to be treated with base to neutralize the acidic nature. The chemicals used to adjust the pH of the soil include calcium hydroxide and calcium carbonate which are base.

(c) Soap-less soaps:

• Universally, anything that cleanses dirt is called soap.  
• But, the body wash made of oil and fats is called soap. The detergents are active chemical substance made up of synthetic cleaners (magnesium and calcium ions) which cannot be used as body cleaners.
• So, detergent is a soap-less soaps.

Advantages of detergents over soaps:

1. Detergents work better than soaps in hard water.

2. Manufacturing of detergents consumes less natural resources and manufacturing cost is also lesser than soaps.

3. Very effective in cleaning without damaging the colours.

(d) pH indicator:

• The soap is a base and the indicator used is litmus paper.
• The base changes red litmus paper to blue and if the blue litmus paper is used then the colour of the paper remains unchanged.