Paper: CSIR-NET December 2016 · Subject: Physical Chemistry · Chapter: Surface Chemistry · Topic: Surface Chemistry – General · Marks: 2 · Difficulty: Medium
When $1 \times 10^{-5}$ g of a fatty acid ($\mathrm{M}=602.3$ g/mol) was placed on water as a surface film, a monomolecular layer of area $100\,\mathrm{cm^{2}}$ was formed on compression. The cross-sectional area (in $\mathrm{\mathring{A}}^{2}$) of the acid molecule is
(a)50
(b)100
(c)150
(d)200
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Molecules = (10⁻⁵/602.3) × 6.022×10²³ = 1.0×10¹⁶; area per molecule = 100 cm² (10¹⁸ Ų)/10¹⁶ = 100 Ų.