An aqueous solution of urea has a freezing point of \(-0.52^oC\). Predict the osmotic pressure of the solution at \(37^oC\) [\(K_f\) =1.86, assuming that the molar concentration and molality are numerically equal]
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 7.1 atm
First find the molality from the depression in freezing point, then use it as the molar concentration in the osmotic pressure equation.
ΔTf = 0 − (−0.52) = 0.52 K
ΔTf = Kf m ⇒ m = 0.52 / 1.86 = 0.2796 mol kg−1
Taking C = 0.2796 mol L−1 and T = 37 + 273 = 310 K:
π = CRT = 0.2796 × 0.0821 × 310
π = 7.12 atm ≈ 7.1 atm