In dialysis, what happens when a hypertonic solution is used?
Dialysis demonstrations use cellophane or cellulose acetate bags with pore diameters permitting water and small molecules under few nanometers while excluding colloids like starch or proteins. When bag containing dilute salt or dye solution is immersed into beaker with concentrated solution hypertonic relative to bag contents, solute concentration inside lower than outside, water potential inside higher. Water activity gradient drives net efflux from interior to exterior attempting to equalize potentials and dilute outer compartment. Membrane remains impermeable to large solutes, so water move
Ref: Lodish et al., Molecular Cell Biology, Chapter: Dialysis and Osmotic Water Movement from Bags.
