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Q82 (NDA-II/2010) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

By which one among the following mechanisms, soap removes dirt (soil) from cloth?

Result
Your answer: —  Â·  Correct: D
Explanation

Soap molecules are sodium or potassium salts of long-chain carboxylic acids with a dual nature: a hydrophilic (water-attracting) ionic head and a hydrophobic (water-repelling) hydrocarbon tail [c1, t3]. Most dirt is oily and does not dissolve in water alone [c1]. When soap is applied, the hydrophobic tails attach to the oily dirt while the ionic heads interact with water, forming spherical structures called micelles [c1, t2]. These micelles encapsulate the oily particles, effectively lifting the soil off the fabric surface [c2, t6]. The soap then keeps these particles suspended in the water as an emulsion, preventing them from redepositing on the cloth [t1, t8]. This suspension allows the dirt to be easily rinsed away during the washing process [t2, t6]. Mechanisms involving direct dissolution of soil or conversion into silicates are chemically incorrect in this context.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.10 > p. 75
  2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 7: Particulate Nature of Matter > Ever heard of ... > p. 111
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