Reverse Osmosis
Definition and meaning of Reverse Osmosis in chemistry.
Reverse osmosis is a separation process that uses applied pressure to force a solvent (usually water) through a semipermeable membrane against its osmotic gradient, moving solvent molecules from a concentrated solution toward a dilute solution, opposite to the direction of natural osmosis.
In more detail
In normal osmosis, water spontaneously migrates across a semipermeable membrane from a dilute solution toward a more concentrated one. Reverse osmosis applies external pressure exceeding the solution's osmotic pressure, reversing this flow and effectively separating dissolved salts, minerals, and other impurities from water. This process is fundamental to water purification and desalination, removing ions and molecules too small for mechanical filters to catch.
Key facts
| Field | Physical Chemistry |
|---|---|
| Membrane type | Semipermeable, with pores approximately 0.0001 to 0.001 micrometers |
| Required pressure | Must exceed the solution's osmotic pressure gradient |
| Primary applications | Water desalination, brackish water treatment, salt removal |
Reverse osmosis systems remove dissolved salts and contaminants from seawater or brackish groundwater, producing fresh drinking water. Industrial desalination plants and residential undersink filters both use RO membranes to achieve this separation.
Frequently asked questions
How does reverse osmosis differ from regular filtration?
Filtration removes particles mechanically using filter pores. Reverse osmosis uses pressure to overcome osmotic forces and separate dissolved ions and molecules much smaller than mechanical filters can remove.
Why must external pressure be applied?
Natural osmosis drives solvent toward concentrated solutions. Applied pressure overcomes this spontaneous thermodynamic tendency, forcing the solvent in the opposite direction to purify it.