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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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During the cleansing action of soap, which end of the soap molecule attaches to the oil/grease droplet?
Hydrophilic end
Hydrophobic end
Ionic end
Carboxylic acid end
Hydrophobic end
Soap molecules are amphiphilic; the non‑polar (hydrophobic) tail attaches to the oil/grease droplet while the polar (hydrophilic) head remains in water.
Soap molecules are amphiphilic; the non‑polar (hydrophobic) tail attaches to the oil/grease droplet while the polar (hydrophilic) head remains in water.
Like a tiny brush whose bristly end (hydrophobic) grabs the greasy stain while the handle (hydrophilic) stays in the water.
Hydro‑PHObic tail = Puts on Grease
CMC=total surfactant concentrationconcentration of monomers — the critical micelle concentration at which micelles form
In water, soap molecules arrange themselves into micelles: the hydrophobic tails congregate around the oil droplet forming its core, and the hydrophilic heads face outward interacting with water, thereby emulsifying the grease and allowing it to be washed away.
Soap molecules have a long non‑polar hydrocarbon chain and a polar carboxylate head.
Micelle formation reduces interfacial tension and disperses oil into fine droplets.
Effective removal of non‑polar soils
Biodegradable when derived from natural fats
Reduced efficiency in hard water due to calcium/magnesium precipitation
Can leave residue if not rinsed well
Household detergents
Emulsifiers in food and cosmetics
| Feature | Soap | Detergent |
|---|---|---|
Source | Natural (fatty acid salts) | Synthetic (sulfonates) |
Typical hydrocarbon chain length is C12‑C18, providing optimal balance of hydrophobicity and solubility.
Option A (Hydrophilic end) is water‑loving and stays in the aqueous phase, not the oil droplet; Option C (Ionic end) and D (Carboxylic acid end) refer to the same polar head group, not the part that contacts oil.
B is correct — the hydrophobic end of a soap molecule attaches to the oil/grease droplet.
Recall that “hydro‑phobic” means ‘fearing water’, so the tail avoids water and seeks the oil layer.