Unit 2 · Free note

Water potential in 3 lines

Water moves from higher Ψ to lower Ψ. Pure water at atmospheric pressure is Ψ = 0. Solute makes Ψs negative, so adding solute lowers Ψ.

1. Ψ = Ψs + Ψp
2. Ψs = −iCRT (more solute → more negative)
3. Compare two sides of a membrane; water goes toward the more negative Ψ

Trap: “Water follows salt” is sloppy. Write the potentials.

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