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Solutions

Solutions. (dilute). Concentration units. M. = molarity. moles of solute. L of solution. mol of solute. X. = mol fraction. mol solute + mol solvent. weight %. mass of solute. x 100. mass of solution. m. = molality. moles of solute. kg solvent. Henry’s Law.

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Solutions

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  1. Solutions (dilute) Concentration units M = molarity moles of solute L of solution mol of solute X = mol fraction mol solute + mol solvent weight % mass of solute x 100 mass of solution m = molality moles of solute kg solvent

  2. Henry’s Law pressure and solubility of gases kH (water) P = kH X O2 4.34 x 104 atm N2 8.57 x 104 atm 1 atm 8.9 atm = 8.57 x 104 = 8.57 x 104 Xnitrogen Xnitrogen [N2] = 0.65 x 10-3 M [N2] = 5.8 x 10-3 M if gases react with water CO2 (g) + H2O  H2CO3 (aq) 4O2(g) + Hb  Hb(O2)4 NH3 (g) + H2O  NH4+ (aq) + OH- (aq)

  3. solute Vapor Pressure of Solutions vapor pressure of liquid evaporation condensation water 25oC Pwater = 23.76 torr add 162 g sugar to 1.0 L Psolution = 23.57 torr pure solvent qualitatively Raoult’s Law fewer solvent molecules at surface Psolution = Xsolvent Posolvent

  4. Raoult’s Law Psolution = Xsolvent Posolvent water 25oC Pwater = 23.76 torr add 162 g sugar to 1.0 L Xsolvent = = 23.57 Psolution Psolution = 23.57 torr 23.76 Posolvent Xsolvent = nwater 0.992 = 0.992 = 55.51 55.51 + x nwater + nsugar x = 0.44 molsugar 1.0 L = 1000 g = 55.51 mol 18.02 g/mol 162 g sugar  molecular weight of sucrose = 365 g/mol 0.44 molsugar

  5. Powater = PowaterXwater Psolution >

  6. Raoult’s Law two volatile components Psolution = = PoA XA + PoB XB gas = PA liquid + PB Daltons Law XB = PB = 15.0 = .36 mix 80 mol A + 20 mol B 32.6 PA + PB What is Ptot ? Ptot = 17.6 + 15.0 = 32.6 PA Ptotal 75 PB (torr) PoA = 22 (torr) 22 / (80+20) = 0.8 = 80 XA 1 XA 0 PoB = 75 0 XB 1 = 20/(80+20) = 0.2 XB

  7. Fractional Distillation Potoluene = 22 = 0.8 Xtoluene Xtoluene = .64 Pobenzene = 75 = 0.2 Xbenzene Xbenzene = .36 Potoluene = 22 Xtoluene Xtoluene = .34 = .64 Pobenzene = 75 Xbenzene Xbenzene = .66 = .36 Ptoluene Ptotal 75 Pbenzene (torr) (torr) 22 Ideal solution 1 Xtoluene 0 0 Xbenzene 1

  8. Raoult’s Law two volatile components Ideal solution LDF benzene toluene LDF LDF higher vapor pressure

  9. Raoult’s Law two volatile components acetone water non-ideal solution H-bonding IMFsoln > IMFcomponents H-bond dipole-dipole Vsoln < Vacetone + Vwater increase P.E.soln K.E.soln increase decrease decrease Tcomponents Tsolution >

  10. Raoult’s Law two volatile components acetone water non-ideal solution negative deviation mixing exothermic Hmixing < 0 229 Poacetone Powater 23.8 Xacetone Xwater

  11. Raoult’s Law two volatile components CHCl3 C2H5OH non-ideal solution dipole-dipole positive deviation dipole-dipole mixing endothermic H-bond Hmixing > 0 194 Poethanol Pochloroform 59.0 Xchloroform Xethanol

  12. Raoult’s Law Psolution = Xsolvent Posolvent lower P of solution raise boiling point of solution Tb = b.p. solution - b.p. solvent KB m KB molal boiling-point elevation constant Tb = = 0.51 kg K/mol = 0.34 mol molality of solution (mol solute/kg solvent) m 0.500 kg What is Tb? 20 g NaCl 500 mL water x 0.68 = 0.35 K Tb = 0.51 kg K/mol 100.79oC NaCl electrolyte 2 mol particles / mol formula Colligative Property

  13. Colligative Property Tb = KB = moles of particles m i i moles of solute i (expected) i (observed) non-electrolyte glucose 1 1 electrolyte NaCl 2 1.9 FeCl3 4 3.4 HCl 2 1.9

  14. Freezing point depression m KF KF molal freezing-point depression constant Tf = i molality of solution (mol solute/kg solvent) m 0.05 m NaNO3 0.075 m CuSO4 0.06 m (NH4)2SO4 0.14 m sucrose

  15. Osmotic Pressure cellular biology molecules across membranes cell membrane permeable to water impermeable to protein, etc.  = gh  = MRT most accurate of colligative properties

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