Osmotic pressure converter
Convert osmolarity into the pressure it exerts across a membrane, and into the pressure a reverse osmosis plant must beat.
That's about the same as blood plasma. That would hold up a column of water about 75.84 meters tall.
What it means
How hard does it pull?
Van ’t Hoff’s law is exact only for dilute solutions at 25 °C. Concentrated brines deviate, which is why desalination plants use measured data.
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Learn
Three things worth knowing
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1 osmol/L = 24.8 bar
Blood plasma at 290 mOsm/L exerts 7.2 bar — about 100 psi, held back by nothing more than a cell membrane.
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Van ’t Hoff won the first Nobel for it
He showed that dissolved particles exert a pressure by the same law as a gas: π = cRT. It earned the first Nobel Prize in Chemistry in 1901.
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Particles, not molecules
A mole of salt makes two moles of particles and twice the pressure of a mole of sugar. Osmosis counts what is dissolved, not what was poured in.
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Background
About osmotic pressure
Put fresh water on one side of a membrane and salt water on the other, and water is pulled across. Osmotic pressure is what it would take to stop it: at 25 °C, one osmole per liter is 24.8 bar.
Seawater at 1.1 osmol/L pulls with 27 bar, which is why reverse osmosis has to push at 55 or more.