Applying pressure greater than osmotic pressure to force solvent out of concentrated solution, used for desalination.
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Reverse osmosis is a membrane process in which an applied pressure greater than the osmotic pressure forces solvent through a semipermeable membrane out of a concentrated solution into a dilute one. In normal osmosis, solvent flows toward the more concentrated side, and applying pressure above the osmotic pressure reverses that flow. The membrane retains dissolved salts and other solutes, so only purified water passes through. The process is widely used for desalinating seawater and for producing ultrapure water for electronics and pharmaceuticals. It requires a large energy input because the pressures needed are high.
Key ideas: Required applied pressure exceeds Pi of the feed, with practical values 55 to 70 atm for seawater at 35 g/L salt, and about 10 to 15 atm for brackish water. Recovery is typically 40 to 50 percent for seawater and the rest is concentrated brine. Energy use is about 3 to 4 kWh per cubic metre, with energy recovery devices cutting it.
Common mistakes and connections: A misconception is that reverse osmosis filters like a sieve only by size; it also relies on solution-diffusion through the dense polymer. Another is expecting full removal of all species; small neutral molecules may pass. Membranes foul and need pretreatment. Links to osmotic pressure, desalination and water purification.
Reverse osmosis applies pressure above the osmotic pressure (about 27 atm for seawater) to force pure water through a membrane. The interactive lesson shows this as a live animation or chart.
Seawater has an osmotic pressure of about 27 atm, so reverse osmosis plants must apply roughly 50 to 70 atm to produce fresh water.
Applying pressure greater than osmotic pressure to force solvent out of concentrated solution, used for desalination.
Reverse Osmosis is a advanced topic in States of Matter & Solutions. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in States of Matter & Solutions first: Freezing Point Depression, Osmosis, Osmotic Pressure.
The next topics in States of Matter & Solutions are van't Hoff Factor and Abnormal Molar Mass.
Yes. The interactive lesson includes a self-check question on Reverse Osmosis, and the States of Matter & Solutions quiz draws on every topic in this area.
Reverse Osmosis is topic 92 of 109 in States of Matter & Solutions.