Arrange the following in increasing order of their osmotic pressure generation at 298 K :
(The cell wall is permeable to water and not to the solute molecules)
(A) If a cell containing 0.5 moles of solute dissolved in 1 L of water is immersed in pure water.
(B) If a cell containing 0.25 moles of solute dissolved in 1 L of water is immersed in pure water.
(C) If a cell containing 0.1 moles of solute dissolved in 0.01 L of water is immersed in pure water.
(D) If a cell containing 0.2 moles of solute dissolved in 0.05 L of water is immersed in pure water.
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B) < (A) < (D) < (C)
Osmotic pressure is a colligative property. For a dilute solution at a given temperature it is proportional to the molar concentration of the solute:
\( \displaystyle \pi=CRT,\qquad C=\frac{n}{V} \)
So compare the concentrations inside the cells:
(A) 0.5 mol in 1 L: C = 0.5 mol L−1 — second
(B) 0.25 mol in 1 L: C = 0.25 mol L−1 — first
(C) 0.1 mol in 0.01 L: C = 10 mol L−1 — last
(D) 0.2 mol in 0.05 L: C = 4 mol L−1 — third
Shortcut: (B) is the most dilute and (C) the most concentrated; only Option (3) starts with (B) and ends with (C).