Detergent and Shop

1. Which one of the following is used in the manufacture of soaps? [44th B.P.S.C. (Pre) 2000]

(a) Vegetable oil
(b) Mobil oil
(c) Kerosene oil
(d) Cutting oil

Correct Answer: (a) Vegetable oil

Solution:

Soap is a combination of animal fat or plant oil and caustic soda. When dissolved in water, it breaks dirt away from the surface. Modern soap makers use fat processed into fatty acids, which eliminates impurities and produces water as a by-product instead of glycerin. Many vegetable fats, including olive oil, palm kernel oil, and coconut oil, are also used in soap making.

2. Soap removes grease by: [(e) None of the above / More than one of the above]

(a) Coagulation
(b) Adsorption
(c) Emulsification
(d) Osmosis

Correct Answer: (c) Emulsification

Solution:Emulsifiers are usually long-chain compounds with polar groups, like soap. The soap molecules consist of two parts: (i) a long hydrocarbon chain (C₁₇H₃₅), which is soluble in fat, and (ii) a dissolved polar part in water (COO⁻ Na⁺). During emulsion, the dipolar alkaline group of soap dissolves oil or grease, and the polar group dissolves in water. When rubbed, the greases are suspended in the water in the form of small droplets and flow smoothly with water.

3. What is detergent? [40th B.P.S.C. (Pre) 1995]

(d) Refining agent
(a) Soap
(b) Medicine
(c) Catalyst

Correct Answer: (d) Refining agent

Solution:A detergent is different from soap. It is a surfactant or a mixture of surfactants with cleaning and refining properties in dilute solutions. The most important ingredients in detergents are chemicals called surfactants. Detergent refers specifically to laundry or dish detergent, as opposed to hand soap or other types of cleaning agents. Detergents are commonly available as powders or concentrated solutions.

4. Detergents used for cleaning clothes are: [63rd B.P.S.C. (Pre) 2017]

Correct Answer: (d) Sulfonates

Solution:Detergents used for cleaning clothes are usually alkylbenzene sulfonates, a family of compounds similar to soap but more soluble in hard water.

5. Assertion (A): Detergent easily removes oil and dirt from dirty garments. [U.P.P.C.S. (Pre) 1997]

Reason (R): Detergent increases the surface tension of water.

Code:

(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

Correct Answer: (c) (A) is true but (R) is false.

Solution:Assertion (A) is true because detergent easily removes oil and dirt from dirty garments. Detergents or soaps reduce the surface tension of water by weakening the hydrogen bonds between water molecules, which helps to remove dirt. However, Reason (R) is false because detergents actually reduce surface tension, not increase it.

6. Assertion (A): Synthetic detergents can make more lather in hard water. [I.A.S. (Pre) 2002]

Reason (R): Synthetic detergents form soluble calcium and magnesium salts with hard water.

(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

Correct Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A).

Solution:Detergents differ from soap because they do not form insoluble precipitates with calcium and magnesium salts in hard water. This is why detergents produce more foam with hard water and remove oil and dust more effectively.

7. Consider the following statements: [I.A.S. (Pre) 2003]

Sodium silicate and sodium sulphate are mixed as detergents in washing powders so that:

To maintain dryness of the powder.
To maintain the basicity of the powder.

Which of the following statements is correct?

(a) only 1
(b) only 2
(c) both 1 & 2
(d) None of both

Correct Answer: (c) both 1 & 2

Solution:Sodium sulphate is added to maintain dryness, while sodium silicate is added to maintain the basicity of the washing powder. The sodium silicate makes the powder crystalline, helping it remain dry.