Osmotic Pressure

Separated Solutions Semipermeable membrane- separates a sol’n and pure solvent, but only allows pure solvent to pass through

Osmosis The vol of the sol’n will increase and the solvent will decrease The flow of solvent is osmosis

Equilibrium Liquid levels eventually stop changing to equilibrium There will be greater pressure on the sol’n b/c the liquid levels are different

Osmotic Pressure The extra pressure on the solution is the osmotic pressure Or the minimum pressure that stops osmosis = the osmotic pressure

Colligative Property? You bet! More solute, more osmotic pressure

 = MRT  = osmotic press in atms M = molarity R = gas law const T = temp in Kelvin

A problem The osmotic pressure of a sol’n containing 26.5 mg of aspartame per L is 1.70 torr at 30oC. Calculate the molar mass of aspartame

Electrolyte sol’ns Remember how we talked about electrolytes contribute the number of ions that they dissociate into???

van’t Hoff factor i Not every single molecule dissociates, so i is the value for the actual dissociation It will be given to you

Easy changes Our eqns are now: T = imK (freezing or boiling)  = iMRT

Homework P 545 67, 69, 77