Question

50 mL of 0.2 molal urea solution (density = 1.012 g mL⁻¹ at 300 K) is mixed with 250 mL of a solution containing 0.06 g of urea. Both solutions were prepared in the same solvent. The osmotic pressure (in Torr) of the resulting solution at 300 K is ___. 
[Use: Molar mass of urea = 60 g mol⁻¹ ; gas constant, R = 62 L Torr K⁻¹ mol⁻¹; Assume, Δ_mixH = 0, Δ_mixV = 0]

Answer 1

Correct Answer: 682

The osmotic pressure (in Torr) of the resulting solution at 300 K is \(\underline{682}\).
Mole of Urea = 0.2
Weight of Urea = \(0.2\times60=12g\)
Weight of solvent = 1000 g
\(\therefore\) The volume of solution = \(\frac{1012}{1.012}=1000\,\,ml\)
\(\therefore\) 50 ml solution contains = \(\frac{0.2\times50}{1000}=0.01\)
\(\therefore\) The concentration of solution = \(\frac{0.01+0.001}{\frac{300}{1000}}\) = 0.0366
\(\therefore \, \pi=CRT=0.0366\times62\times300=682\)