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Chemistry Question 54 – JEE-MAIN 2026

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At 27∘C, 0.1 M, 1 L K4[Fe(CN)6] aqueous solution and 0.1 M, 1 L FeCl3 aqueous solution are placed in a container separated by a semi permeable membrane AB. Assume complete dissociation of both the solutes. Which of the following statement is \textit{correct}? Side 'x': 0.1 M, 1 L K4[Fe(CN)6] Side 'y': 0.1 M, 1 L FeCl3

Recall that osmosis involves the movement of solvent across a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration. Tonicity (hypotonic, hypertonic, isotonic) describes the relative solute concentrations of two solutions.

Step 1: Calculate Effective Concentrations✦ Active

First, determine the van't Hoff factor (i) for each solute, assuming complete dissociation, and then calculate the effective concentration (Ceff=i×C) for each side.

For side 'x' (K4[Fe(CN)6]): K4[Fe(CN)6]→4K++[Fe(CN)6]4− ix=4+1=5 Ceff,x=0.1 M×5=0.5 M For side 'y' (FeCl3): FeCl3→Fe3++3Cl− iy=1+3=4 Ceff,y=0.1 M×4=0.4 M
Step 2: Determine Tonicity and Osmosis Direction○ Expand

Compare the effective concentrations to determine the tonicity of each solution relative to the other and the direction of solvent flow.

Since Ceff,x(0.5 M)>Ceff,y(0.4 M), side 'x' is hypertonic relative to side 'y', and side 'y' is hypotonic relative to side 'x'. Water will flow from side 'y' to side 'x'.

💡 Teacher's Secret Hint

Remember that water moves from a hypotonic (lower solute concentration) region to a hypertonic (higher solute concentration) region.

Step 3: Evaluate Options○ Expand

Based on the calculations and principles of osmosis:

1. "Blue color is formed on both sides." Incorrect. Semi-permeable membranes typically do not allow large ions like Fe3+ or complex ions like [Fe(CN)6]4− to pass, so no reaction to form Prussian blue will occur.

2. "Ionic solutes in aqueous solution can pass through semi-permeable membrane." Incorrect. Semi-permeable membranes are selectively permeable, allowing solvent (water) but restricting solute movement.

3. "Solution on side 'y' is hypotonic." Correct. As determined in Step 2, side 'y' has a lower effective solute concentration (0.4 M) compared to side 'x' (0.5 M), making it hypotonic.

4. "To cause the reverse flow of solvent during osmosis, external pressure (any value) should be applied to side 'x'." Incorrect. While pressure must be applied to the hypertonic side ('x') to cause reverse osmosis, it must be a pressure *greater than* the osmotic pressure, not just "any value".

💡 Teacher's Secret Hint

Carefully consider the implications of 'semi-permeable' and the specific conditions required for reverse osmosis.

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