Question

$6g$. of the area of dissolved in $90g$. of boiling water. The vapour pressure of the solution is:

• A. $744.8$ mm
• B. $758$ mm
• C. $761$ mm
• D. $760$ mm

Answer 1

The correct option is A $744.8$ mm

Vapour pressure $P=P°x,P°=$Boiling point of pure solvent

$P=P°\frac{n_1}{n_1+n_2}$

$=760\left(\frac{0.1}{0.1+5}\right)90g{H}_{2}O=5mol=n_2;6g$ urea$=0.1mol=n_1$

$=760\left(\frac{0.1}{0.1+5}\right)$

$=760\times 0.0196=14.89$ Torr=lowered pressure

Now, 1 torr = 1 mm of Hg

Vapour pressure of solution$=760-14.89\approx 744.8mmofHg$
Option A is correct.