MCQ
$10\, mL$ of $1\,mM$ surfactant solution forms a monolayer covering $0.24\, cm^2$ on a polar substrate. If the polar head is approximated as cube, what is its edge length ?
  • $2.0\,pm$
  • B
    $2.0\,nm$
  • C
    $1.0\,pm$
  • D
    $0.1\,nm$

Answer

Correct option: A.
$2.0\,pm$
a
$Moles = \frac{{MV\,ml}}{{1000}} = \frac{{{{10}^{ - 3}} \times 10}}{{1000}} = {10^{ - 5}}\,mole$

$10^{-5}$ $N_A$ molecules covering area $= 0.24\,cm^2$

$1$ molecules covering area $ = \frac{{0.24}}{{{{10}^{ - 5}}\,{N_A}}}$

$\frac{{0.24}}{{{{10}^{ - 5}}\, \times 6 \times {{10}^{23}}}} = {a^2}$

$a^2 = 4 \times 10^{-20}\,cm^2$

$a = 2 \times 10^{-10}\,cm$

$a = 2 \times 10^{-12}\,cm$

$a = 2\,pm$

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