A Conversation for Osmosis


Post 1


See the chapter "The Osmotic Pressure". If dissolved particles behave like gas particles, they will try to expand the volume of the solvent. This puts the solvent under tension, or negative pressure. So in a cup of tea with sugar the water is under a tension equal the the osmotic pressure caused by the sugar. (Note an error in the Example: 18 grams of sucrose is not 0.1 mol. The molar weight of sucrose is 342).

When a solution of sugar is separated from pure water by a semi-permeable membrane, water will flow through the membrane from the pure water to the solution because the water pressure in the solution is lower than in the pure water. If the sugar solution is put in a closed container in contact with pure water through a semipermeable membrane, water will move into the sugar solution until the water pressure is equal on both sides of the membrane. The pressure in the closed container will therefore rise by an amount equal the osmotic pressure.

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