Reverse Osmosis and Colligative Properties

Also called

reverse osmosis · osmotic pressure · pi = CRT · van 't Hoff equation · semipermeable membrane · colligative properties · desalination · RO water purifier · elevation of boiling point · depression of freezing point · antifreeze · ethylene glycol · salt on icy roads · molal elevation constant · उत्क्रम परासरण · परासरण दाब · अणुसंख्य गुणधर्म

Topics

• In osmosis solvent molecules pass through a semipermeable membrane from pure solvent into a solution.
• Osmotic pressure is the extra pressure that just stops osmosis; for a dilute solution π = CRT.
• The solution column rises until the pressure of its extra height h balances the osmotic pressure.
• A pressure larger than π on the solution pushes water the other way through the membrane: reverse osmosis.
• The membrane passes water but holds back Na⁺ and Cl⁻ ions, so fresh water collects on the other side.
• An RO purifier: sediment filter, carbon filter, pump and RO membrane; the salty reject goes to the drain.
• A solution boils at a higher temperature than the pure solvent: ΔTb = Kb·m.
• A solution freezes at a lower temperature than the pure solvent: ΔTf = Kf·m.
• Antifreeze (ethylene glycol) in car radiators and salt on icy roads use the lowering of the freezing point.

About this model

A GLB file of about 768 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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