Question

A solution of palmitic acid (Molar mass $=256gm$ ) in benzene contains $5.12gm$ of acid per litre. When this solution is dropped on a surface, benzene evaporates and palmitic acid forms a monolayer. If we wish to cover an area of $480cm^{2}$ with a monolayer of volume $X\times 10^{- 2}mL$ of solution should be used. Area occupied by one palmitic molecules $\left.=0.2 nm ^{2}\right\}\left\{ N _{ A }=6 \times 10^{23}\right\}$, Calculate value of $X ?$ ?

Answer 1

No. of molecules in $'V'$ litre
$=\frac{5 .12 \times V}{256}\times 6\times 10^{23}=1.2\times 10^{22}V$
Area covered $=\left(1.2 \times 10^{22} V \times 0.2 \times 10^{-14}\right) cm ^{2}$
$=2.4\times 10^{7}Vcm^{2}$
$2.4\times 10^{7}V=480$
$V=2\times 10^{- 5}litre$
$V=0.02ml$