MCQ
If relative decrease in vapour pressure is $0.4$ for a solution containing $1\, mol$ $NaCl$ in $3\, mol$ of $H_2O$, the degree of ionization of $NaCl$ is .......... $\%$.
  • A
    $60$
  • B
    $50$
  • $100$
  • D
    $40$

Answer

Correct option: C.
$100$
c
$\frac{{{{\text{P}}^o} - {{\text{P}}_{\text{S}}}}}{{{{\text{P}}^o}}} = \frac{{{\text{in}}}}{{{\text{in}} + {\text{N}}}}$

$0.4=\frac{i \times 1}{i \times 1+3}$

$0.4 \,\mathrm{i}+1.2= \mathrm{i}$

$0.6 \,\mathrm{i}=1.2$

$i=2$

$\mathop {{\text{NaCl}}({\text{aq}})}\limits_{1 - \,\alpha } \, \rightleftharpoons \mathop {{\text{N}}{{\text{a}}^ + }({\text{aq}})}\limits_\alpha   + \mathop {{\text{C}}{{\text{l}}^ - }({\text{aq}})}\limits_\alpha  $

$1+\alpha=2$

$\alpha=1$   or  $100\%$

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