Chapter 11. Properties of Solutions Solutions

Transcription

1 Chapter 11. Properties of Solutions Solutions Homogeneous Mixture 1

2 Solution Composition Equivalent moles of solute (mol) Acid-Base reaction Molarity (M) = liter of solution (L) 1 eq: the quantity of acid or base that t can furnish or accept 1 mole of H +. Mass (weight) percent Mole fraction ( χ ) A = mass of solute = 100% mass of solution moles of solute A total mols of solution moles of solute (mol) Molality (m) = kilogram of solvent (kg) number of equivalents of solute Normality (N) = liter of solution Redox reaction 1 eq: the quantity of oxidant or reductant that can accept or furnish 1 mole of electrons. MnO e H + --> Mn H 2 O 1 mole of MnO 4- --> 5 eq of MnO 4 - Solution Composition moles of solute (mol) Molarity (M) = liter of solution (L) Mass (weight) percent Mole fraction ( χ ) A = mass of solute = 100% mass of solution moles of solute A total mols of solution moles of solute (mol) Molality (m) = kilogram of solvent (kg) number of equivalents of solute Normality (N) = liter of solution Ex) 3.75 M H 2 SO 4 solution (electrolyte in Pb battery), d=1.230 g/ml --> mass percent, molality, normality? mass percent solution mass in 1 L solution = 1230 g solute mass in 1 L solution = 3.75 mol x 98.1 g/mol = 368 g mass percent = 368g/1230g = = 29.9 % molality solvent mass in 1 L solution = 1230 g g = 862 g moles of solute in 1 L solution = 3.75 mol molality = 3.75 mol/862 g = 3.75 mol/ kg = 4.35 mol/kg = 4.35 m normality solute eq in 1 L solution = 3.75 mol/(2 eq/mol) = 7.50 eq normality = 7.50 eq/l = 7.50 N 2

3 Energies of Solution Formation Heat of solution (ΔH soln = ΔH 1 + ΔH 2 + ΔH 3 ) Energies of Solution Formation Ethanol - Water Oil-Water 3

4 Energies of Solution Formation ΔG = ΔH - TΔS NaCl in Water NaCl(s) Na + (g) + Cl - (g) ΔH 1 = 786 kj/mol H 2 O(l) + Na + (g) + Cl - (g) Na + (aq) + Cl - (aq) ΔHH 2 + ΔHH 3 = ΔHH hyd = -783 kj/mol heat of hydration ΔH 1 ΔH 2 + ΔH 3 = ΔH soln = 3 kj/mol not much favorable, then what happens? Factors affecting solubility Structure effect Pressure effect Temperature effect vitamin i A vitamin C vitamin D 1 hydrophobic hydrophilic 4

5 Pressure effect Factors affecting solubility little effect on the solubility of solids or liquids for gas, solubility as P equilibrium new equilibrium Factors affecting solubility Pressure effect C = kp Henry's Law: The amount of a gas dissolved d in a solution is directly proportional to the pressure of the gas above the solution. P = partial pressure of gaseous solute above the solution C = concentration of dissolved gas k = a constant Ex) Before opening, P CO2 = 5 atm inside of the bottle. C CO2 in the beer solution before and after opening? (P CO2 (air) = 4.0 x 10-4 atm, k CO2 = 3.1 x 10-2 mol/l atm at 25 o C) Before opening, C CO2 = k CO2 P CO2 = (3.1 x 10-2 mol/l atm)x(5atm) = 0.16 mol/l After opening, C CO2 = k CO2 P CO2 (air) = (3.1 x 10-2 mol/l atm)x(4.0x10-4 atm) = 1.2x10-5 mol/l 5

6 Factors affecting solubility Temperature effect (for aqueous solutions) Solid T, speed of dissolving g But solubility depends on the substance to be dissolved. difficult to predict. empirical Factors affecting solubility Temperature effect (for aqueous solutions) Gas T, solubility in water. T, solubility in most nonaqueous solvents. 1 atm 6

7 Factors affecting solubility Temperature effect (for aqueous solutions) thermal pollution Vapor Pressures of Solutions non-volatile solute if P vap (pure water) > P vap (solution) to make equilibrium Nonvolatile solute lowers the vapor pressure of a solvent. 7

8 Vapor Pressures of Solutions number of solvent molecules at the surface P vap Nonvolatile Solute P soln = χ solvent P o solvent Raoult s Law: The presence of a nonvolatile solute lowers the vapor pressure of a solvent. P soln = vapor pressure of the solution, χ solvent = mole fraction of the solvent P solvent = vapor pressure of the pure solvent Vapor Pressures of Solutions Liquid (volatile)-liquid (volatile) solution P total = P A +P B = χ A P o A+χ B P o B χ A + χ B = 1 Ideal solution: A liquid-liquid solution that obeys Raoult's law. CH 3 8

9 Vapor Pressures of Solutions Nonideal solutions: liquid-liquid solution not-obeying Raoult's law P total > χ P o A+χ P o A A χ B B P total < χ A P o A+χ B P o B OH CH 3 CH 2 CH 3 H CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 CH 3 O H δ - δ + O Colligative Properties of Solutions Colligative properties: Properties depend only on the number, not on the identity, of the solute particles in an ideal solution. Boiling-Point Elevation Freezing-Point Depression Osmotic Pressure normal boiling point: temperature where the vapor pressure is equal to 1 atm. 9

10 Colligative Properties of Solutions Boiling-Point Elevation Freezing-Point Depression Nonvolatile Solute ΔT b = k b m solute ΔT f = k f m solute k b : molal boiling-point elevation constant of solvent k f : molal freezing-point depression constant of solvent m solute : molality of solute Colligative Properties of Solutions Boiling-Point Elevation Freezing-Point Depression Nonvolatile Solute ΔT b = k b m solute ΔT f = k f m solute k b : molal boiling-point elevation constant of solvent k f : molal freezing-point depression constant of solvent m solute : molality of solute 10

11 Colligative Properties of Solutions Boiling-Point Elevation Freezing-Point Depression 1 atm, 100 o C 1 atm, 0 o C Steam Water Steam Water T b Ice Water Ice Water T f Colligative Properties of Solutions Boiling-Point Elevation Freezing-Point Depression Ex) Mass of ethylen glycol (C 2 H 6 O 2 ) to make antifreeze with T f = o C in 10.0 L water? (k f = 1.86 o C kg/mol) ΔT = k m m f solute mass f o ΔTf 23.3 C = = = 12.5mol / kg = 125mol /10kg o k 1.86 C kg / mol solute solute f = 125mol 62.1g / mol = 7760g 11

12 Colligative Properties of Solutions Osmotic pressure more semipermiable Osmosis: The flow of solvent into the solution through the semipermeable membrane. Osmotic Pressure: The excess hydrostatic pressure on the solution compared to the pure solvent. Π = MRT M: molarity of solution Colligative Properties of Solutions Osmotic pressure semipermiable membrane: through which only solvent molecules are permeable. NORMAL RED BLOOD CELLS: 0.9% NaCl Isotonic Solution RED BLOOD CELLS - CRENATION: 20.0% NaCl Hypertonic Solution allowing transfer of both solvent molecules and small solute molecules and ions. RED BLOOD CELLS - HEMOLYSIS: Distilled Water Hypotonic Solution 12

13 Colligative Properties of Solutions Osmotic pressure Colligative Properties of Solutions Osmotic pressure Reverse Osmosis 13

14 Colligative Properties of Solutions Colligative Properties of Electrolyte Solutions i = moles of particles in solution moles of solutes dissolved van't Hoff factor ΔT = im solute k Π = imrt Colligative Properties of Solutions Colligative Properties of Electrolyte Solutions Ex) 0.1 M Fe(NH 4 ) 2 (SO 4 ) 2 solution, Π=10.8 atm --> i (25 o C)? Fe(NH 4 ) 2 (SO 4 ) 2 (aq) --> Fe 2+ (aq) + 2NH SO 2-4 expected i = 5 Π = imrt i = Π/MRT = (10.8 atm)/(0.10 mol/l) ( L atm/k mol) (298K) =

15 Colloids Colloids Tyndall Effect 1~1000 nm Colloid: A suspension of tiny particles in some medium. 15

16 Colloids net neutral net neutral Repulsion prevents coagulation Heat or Electrolyte causing coagulation of colloids Colloids Yellow River 16

17 Colloids Yellow River Delta, Yesterday and Today Colloids Yellow River Delta, Yesterday and Today Before 2005 Image date not known Copied from Google Eearth ( ) Image date not known Copied from Google Eearth ( ) Image date not known 17