Question

The vapour pressure of water at ${20}^{o}C$ is 17.53 mm. Calculate the vapour pressure of a solution at ${20}^{o}C$ containing 6 g of urea in 100 g of water (molecular mass of urea = 60).

• A. 17.22 mm
• B. 27.22 mm
• C. 117.22 mm
• D. 136.22 mm

Answer 1

The correct option is A 17.22 mm

we have,

$\frac{P_B^0-P_t}{P_B^0}=x_A$

moles of urea = 6/60 = 0.1 moles

moles of waterc= 100/18 = 5.55 moles

$\frac{17.53-P_t}{17.53}=\frac{0.1}{0.1+5.55}$

we get $P_t=17.219mm$