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On the account of osmotic pressure 'arive ' at the Van't Hoff equation. (##SUR_CHE_XI_V02_C09_E04_015_Q01.png" width="80%"> |
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Answer» SOLUTION :Let us consider a simple apparatus as shown in the above figure . A semi-permeable membrane separtesa chamber into two compartments .WATER (pure solvent ) is added to the first compartment and the aqeuous NaCl ( solution ) is added to the second compartment such that the liquid LEVELS on the both sides are equal . Since there is a difference in concentration between the liquids present in the two compartments . the water molecules move from first compartment .to second compartment through the semi-permeable membrane allows only the water molecules to pass through ith in either direction but not allows the NaCl . The net flow of water is into the sodium chloride solution and hence increase its VOLUME . This decreases its concentration and also creates a pressure difference between the compartment .This pressure difference push some of the water molecules back to the solvent side through the semipermeable membrane until an equilibrium is establised . At the equilibrium the rate of movement of solvent molecules on both directions are equal The pressure difference at the equilibrium is called osmotic pressure `(pi) ` .Thus osmotic preesure can be defined as " the pressure that must be applied to the solution to stop the influx of the solvent (to stop osmosis) through the semipermeable membrane " Van't Hoff found out that for dilute solution the osmotic pressure is directly proportional to the molar concentration of the solute and the tempeerature of the solution . He proposed the FOLLOWING equation to calculate osmotic pressure which is now called as Van't Hoff equation. ` "" pi =cRT ` Here , c= Concentration of the solution in molarity T=Temperature R= Gas constant |
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