1. Physical Properties of Solutions Chapter 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 12.1 A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount

3. A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature. An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature. A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature. Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate. 12.1

4. “like dissolves like” Two substances with similar intermolecular forces are likely to be soluble in each other. non-polar molecules are soluble in non-polar solvents CCl 4 in C 6 H 6 polar molecules are soluble in polar solvents C 2 H 5 OH in H 2 O ionic compounds are more soluble in polar solvents NaCl in H 2 O or NH 3 (l) 12.2 Two liquids are said to be miscible if they are completely soluble in each other in all proportions.

6. Concentration Units The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. Percent by Mass % by mass = x 100% mass of solute mass of solute + mass of solvent = x 100% mass of solute mass of solution 12.3 Percent by Mole [Mole Fraction (X)] X A = moles of A sum of moles of all components

7. Concentration Units Continued M = moles of solute liters of solution Molarity (M) Molality (m) m = moles of solute mass of solvent (kg) 12.3

9. Comparison of concentration unit Mole fraction is often used for gaseous vapor. Molarity is temperature dependent. Because Molarity is dependent upon volume. Volume is the only unit present in these different values that would change with temperature. The volume of an aqueous solution will increase with increased temperature. Thus, the molarity of a given solute will decrease when the solution is heated. Molality, mass percentage and mole fraction are not temperature dependent.

10. What is the molality of a 5.86 M ethanol (C 2 H 5 OH) solution whose density is 0.927 g/mL? m =m = moles of solute mass of solvent (kg) M = moles of solute liters of solution Assume 1 L of solution: 5.86 moles ethanol = 270 g ethanol 927 g of solution (1000 mL x 0.927 g/mL) mass of solvent = mass of solution – mass of solute = 927 g – 270 g = 657 g = 0.657 kg m =m = moles of solute mass of solvent (kg) = 5.86 moles C 2 H 5 OH 0.657 kg solvent = 8.92 m 12.3

12. Temperature and Solubility Solid solubility and temperature solubility increases with increasing temperature solubility decreases with increasing temperature 12.4

13. Temperature and Gas Solubility O 2 gas solubility and temperature solubility usually decreases with increasing temperature 12.4 On a hot summer day, an experienced fisherman usually picks a deep spot in the river or lake to cast bait. Why??

14. Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 12.6 Vapor-Pressure Lowering Boiling-Point Elevation Freezing-Point Depression Osmotic Pressure (  )

15. Vapor-Pressure Lowering Raoult’s law—the partial pressure of a solvent over solution, P 1, is given by the vapor pressure of the pure solvent, P 1 0, times the mole fraction of the solvent in the solution, X 1. If the solution contains only one solute: X 1 = 1 – X 2 P 1 0 - P 1 =  P = X 2 P 1 0 0 = vapor pressure of pure solvent X 1 = mole fraction of the solvent X 2 = mole fraction of the solute 12.6 P 1 = X 1 P 1 0 The decease in vapor pressure,  P, is directly proportional to the solute concentration (measured in mole fraction)

16. Worked Example 12.7

17. Boiling-Point Elevation  T b = T b – T b 0 T b > T b 0  T b > 0 T b is the boiling point of the pure solvent 0 T b is the boiling point of the solution  T b = K b m m is the molality of the solution K b is the molal boiling-point elevation constant ( 0 C/m) for a given solvent 12.6

18. Freezing-Point Depression  T f = T f – T f 0 T f > T f 0  T f > 0 T f is the freezing point of the pure solvent 0 T f is the freezing point of the solution  T f = K f m m is the molality of the solution K f is the molal freezing-point depression constant ( 0 C/m) for a given solvent 12.6 Ice on frozen roads melts when sprinkled with salts. Why??

19. 12.6

20. What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is 62.01 g.  T f = K f m m =m = moles of solute mass of solvent (kg) = 2.41 m = 3.202 kg solvent 478 g x 1 mol 62.01 g K f water = 1.86 0 C/m  T f = K f m = 1.86 0 C/m x 2.41 m = 4.48 0 C  T f = T f – T f 0 T f = T f –  T f 0 = 0.00 0 C – 4.48 0 C = -4.48 0 C 12.6

21. Osmotic Pressure (  ) 12.6 Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one. A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules. Osmotic pressure (  ) is the pressure required to stop osmosis. dilute more concentrated

22. High P Low P Osmotic Pressure (  )  = MRT M is the molarity of the solution R is the gas constant T is the temperature (in K) 12.6

23. Worked Example 12.9

24. Colligative Properties of Nonelectrolyte Solutions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 12.6 Vapor-Pressure Lowering P 1 = X 1 P 1 0 Boiling-Point Elevation  T b = K b m Freezing-Point Depression  T f = K f m Osmotic Pressure (  )  = MRT

25. Worked Example 12.10

26. Colligative Properties of Electrolyte Solutions 12.7 0.1 m NaCl solution 0.1 m Na + ions & 0.1 m Cl - ions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 0.1 m NaCl solution0.2 m ions in solution van’t Hoff factor (i) = actual number of particles in soln after dissociation number of formula units initially dissolved in soln nonelectrolytes NaCl CaCl 2 i should be 1 2 3

27. Boiling-Point Elevation  T b = i K b m Freezing-Point Depression  T f = i K f m Osmotic Pressure (  )  = iMRT Colligative Properties of Electrolyte Solutions 12.7

28. Figure 12.14 Ion-pair formation