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#U-tube experiment

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Membrane Transportation

In a U-tube experiment, if Side A has 4M NaCl and Side B has 10M NaCl, what will be the movement of water?

Demonstration using U-tube separated by membrane permeable only to water nicely illustrates colligative water movement. Osmotic pressure approximated by van't Hoff law pi equals i times C times R times T proportional to total particle concentration. Solution A holding 4 molar NaCl dissociates into sodium and chloride giving factor near two, so effective osmolarity roughly 8 osmoles, solution B 10 molar near 20 osmoles, markedly higher. Chemical potential of water mu equals mu naught plus RT ln a water minus V bar P, and a water declines with solute. Therefore water potential higher in dilute a

Ref: Nelson & Cox, Lehninger Principles of Biochemistry, Chapter 11: Osmosis and Water Movement Between Compartments.

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Membrane Transportation

In a U-tube experiment, water moves from:

A classical U-tube experiment visualizes osmosis by dividing tube into two arms with a membrane impermeable to solute like sodium chloride but permeable to water via narrow pores or aquaporin analogues. Each arm filled with aqueous solution of different concentration. Water activity and chemical potential are inversely related to solute concentration; lower solute means more free water molecules with higher escaping tendency. Consequently random thermal motion results in greater diffusive flux of water from low solute concentration side where water concentration high toward high solute side wh

Ref: Lodish et al., Molecular Cell Biology, Chapter: Osmosis and U-Tube Demonstration of Water Movement.

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