Osmosis is the phenomenon of water flow through a semi permeable membrane that blocks the transport of salts or other solutes through it.

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Osmosis

Osmosis is the phenomenon of water flow through a semi permeable membrane that blocks the

transport of salts or other solutes through it. Osmosis is a fundamental effect in all biological

systems. It is applied to water purification and desalination, waste material treatment, and many

other chemical and biochemical laboratory and industrial processes.

When two water (or other solvent) volumes are separated by a semi permeable membrane,

water will flow from the side of low solute concentration, to the side of high solute

concentration. The flow may be stopped, or even reversed by applying external pressure on the

side of higher concentration. In such a case the phenomenon is called reverse osmosis.

If there are solute molecules only in one side of the system, then the pressure that stops the flow

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is called the osmotic pressure.

The movement of a solute molecule within a solvent is over damped by the solvent molecules

that surround it. In fact, the solute movement is wholly determined by fluctuations of thermal

collisions with nearby solvent molecules. However, the average thermal velocity of the molecule

is the same had it been free in a gas phase

Whenever a solute movement is blocked by a wall it will transfer momentum to it and, therefore,

generate pressure on it. Since the velocity is the same as that of a free molecule, the pressure ...

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