Lecture5_S08

Lecture5_S08 - Lecture 5 Final Colligative property is...

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Lecture 5 Final Colligative property is osmotic pressure: Osmosis describes the net movement of pure solvent into solutions (with higher concentrations of impurities (solutes)) in order to maximize entropy and mixing. time Flow stops when solution can no longer fight gravity and atmospheric pressure Quantified by: π = i M RT Osmotic pressure (in atm) Temperature (K) Gas constant ( = 0.0821 L*atm/(K*mol)) Molarity (mol/L) van’t Hoff constant For ideal solution of 3.4 g NaCl in 1000 mL H 2 O @ 20 o C, calculate osmotic pressure. Example π = i M RT = i (mol NaCl) RT i = 2 for NaCl = Na + + Cl - T = 20oC = 293 K V soln = 1 L V soln (L) Mol NaCl = 3.4 g NaCl/58.44( g/mol) = 0.05818 mol π = 2(0.05818 mol)(0.0821 L*atm/K*mol)(293 K)/1L π = 2.8 atm
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Finding Molecular Weight using freezing point depression/boiling point elevation (Usually given mass solute, amount solvent, and freezing/boiling point) Δ T f = i K f m For molecular compounds i = 1, so Δ T f = K f m Keeping in mind units for molality (mol solute/kg solvent):
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Lecture5_S08 - Lecture 5 Final Colligative property is...

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