Question

$12\, g$ of a nonvolatile solute dissolved in $108\, g$ of water produces the relative lowering of vapor pressure of $0.1.$The molecular mass of the solute is :

• A. 80
• B. 60
• C. 20
• D. 40

Answer 1

Answer: (C)

20

Answer 2

$\frac{P^{o}-P_{s}}{P^{o}} = \frac{n}{N} = \frac{w}{m}\times \frac{M}{W}$
$0.1= \frac{12}{m} \times \frac{18}{108}$
$m = \frac{12\times18}{0.1\times108} = 20$