If at certain temperature, the vapour pressure of pure water is 25 mm of Hg and that of a very dilute aqueous urea solution is 24.5 mm of Hg, the molality of solution is

Question

If at certain temperature, the vapour pressure of pure water is 25 mm of Hg and that of a very dilute aqueous urea solution is 24.5 mm of Hg, the molality of solution is (A) 0.02 (B) 1.2 (C) 1.11 (D) 0.08

Tardigrade Admin · Accepted Answer

By using the relation, molality =(p°-ps/p°) × (1000/M) Molality (m)=(25-24.5/25) × (1000/18) =(0.5/25) × (1000/18)=1.11 ∴ Molality of solution =1.11 m

Q. If at certain temperature, the vapour pressure of pure water is $25 mm$ of $H g$ and that of a very dilute aqueous urea solution is $24.5 mm$ of $H g$ , the molality of solution is

$0.02$

$1.2$

$1.11$

$0.08$

By using the relation, molality $= \frac{p ^{\circ} - p _{s}}{p ^{\circ}} \times \frac{1000}{M}$
Molality $(m) = \frac{25 - 24.5}{25} \times \frac{1000}{18}$
$= \frac{0.5}{25} \times \frac{1000}{18} = 1.11$
$∴$ Molality of solution $= 1.11 m$

Q. If at certain temperature, the vapour pressure of pure water is 25mm of Hg and that of a very dilute aqueous urea solution is 24.5mm of Hg, the molality of solution is

0.02

1.2

1.11

0.08