Question

A Solution of palmitic acid in benzene contains $4.24\text{g}$ of acid per litre. When this solution is dropped on a surface, benzene evaporates and palmitic acid forms a unimolecular film on the surface. If we wish to cover an area of $500{\text{cm}}^2$ with a unimolecular film, what volume of solution (in litres) should be used? The area covered by one palmitic acid molecule may be taken as $0.21{\text{nm}}^2$.
Molecular weight of palmitic acid = 256 $gmo{l}^{-1}$.

• A. $4.38\times {10}^{-5}$
• B. $2.4\times {10}^{-5}$
• C. $4\times {10}^{-41}$
• D. $56\times {10}^5$

Answer 1

The correct option is B $2.4\times {10}^{-5}$

V litre volume of solution taken.
$W(4.24\times V)g$
Number of atoms $=\frac{W}{Atomicmass}\times Avogadr{o}^{\prime }snumber$
$=\frac{4.24V}{256}\times 6.023\times {10}^{23}$
Area $=500=[\frac{4.24V}{256}\times 6.023\times {10}^{23}]\times 0.21\times {10}^{-18}\times {10}^4$
$V=2.4\times {10}^{-5}L$