Direction of solvent flow in osmosis: Across a semi-permeable membrane, the diffusion of which component goes in which direction?

Introduction / Context:Osmosis is the flow of solvent through a semi-permeable membrane that passes solvent but not solute. It is driven by differences in chemical potential (or equivalently osmotic pressure) across the membrane. This phenomenon underpins desalination, food processing, and biological cell behavior.

Given Data / Assumptions:

• The membrane is semi-permeable: solvent permeates; solute is retained.
• Two solutions are at the same temperature and initially no hydrostatic head is imposed.
• One side is more concentrated in solute than the other.

Concept / Approach:Solvent chemical potential decreases with increasing solute concentration. Consequently, solvent flows spontaneously from the dilute side (low solute concentration, higher solvent chemical potential) to the concentrated side (high solute concentration, lower solvent chemical potential) until mechanical/osmotic equilibrium is achieved or a counter-pressure is applied to stop the flow (reverse osmosis applies pressure to invert the flow).

Step-by-Step Solution:

Verification / Alternative check:Van’t Hoff relation π = i * M * R * T shows osmotic pressure proportional to solute concentration; solvent flow opposes this pressure gradient unless counterbalanced mechanically.

Why Other Options Are Wrong:

• Reverse direction (b): contradicts thermodynamic driving force.
• Solute passing (c): a semi-permeable membrane blocks solute ideally.
• No direction (d) and equal bidirectional flow (e): inconsistent with observed osmotic phenomena.

Common Pitfalls:Confusing 'concentration' to mean solvent concentration instead of solute; forgetting that the membrane is selective.

Final Answer:Solvent flows from the low solute concentration side to the high solute concentration side