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

2. Chapter 12 Physical Properties of Solutions 1. Use the terms saturated, unsaturated and supersaturated to describe solutions. 2. Distinguish between crystallization and precipitation. 3. Predict relative solubilities given the next dipole moment of solute and solvent. 4. Define, determine and inter-convert between each of the following: * molarity * percent by mass * mole fraction * molality 5. Suggest a shortcoming of molarity and explain why molality is a preferred concentration unit under certain conditions. 6. Use the concept of fractional crystallization to show how dissolved solids can be separated. 7. Describe how thermal pollution may effect the oxygen content in lakes or streams.

3. 8. State Henry’s law and use it to determine the solubility of gases in liquids. 9. Rationalize why two common materials (NH 3 or CO 2 ) when dissolved in water do not follow Henry’s law. 10. Define colligative properties and give four examples (vapor – pressure lowering, freezing – point lowering, boiling – point elevation and osmotic pressure). 11. Use Raoult’s law to find vapor pressures or concentrations of solutions. 12. Describe the apparatus used in fractional distillation. 13. Predict the plot of pressure versus mole fraction for an ideal solution. 14. Rationalize the possibility of either positive or negative deviations from Raoult’s law by non-ideal solutions. 15. Perform calculations involving boiling-point elevation, freezing-point depression, K f, K b and molality. 16. Use the concepts of osmotic pressure to describe the processes of osmosis and reverse osmosis.

4. 17. Describe the following terms: *semi-permeable membrane *isotonic *hypertonic *hypotonic *crenation 18. Use the concepts of colligative properties to determine molar mass. 19. Define the van’t Hoff factor and demonstrate how it is incorporated into the colligative property equations. 20. Give examples of common types of colloids and describe the dispersing medium and dispersed phase for each. 21. Describe the Tyndall effect. 22. Identify hydrophilic and hydrophobic colloids and describe the cleansing action of soap.

5. 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

6. 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. A supersaturated solution contains more solute than is present in a saturated solution. Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate. 12.1

7. 12.2 Three types of interactions in the solution process: solvent-solvent interaction solute-solute interaction solvent-solute interaction  H soln =  H 1 +  H 2 +  H 3

8. “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

9. 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 Mole Fraction (X) X A = moles of A sum of moles of all components

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

11. 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. Fractional crystallization is the separation of a mixture of substances into pure components on the basis of the differing solubilities. Suppose you have 90 g KNO 3 contaminated with 10 g NaCl. Fractional crystallization: 1.Dissolve sample in 100 mL of water at 60 0 C 2.Cool solution to 0 0 C 3.All NaCl will stay in solution (s = 34.2g/100g) 4.78 g of PURE KNO 3 will precipitate (s = 12 g/100g). 90 g – 12 g = 78 g 12.4

14. Temperature and Solubility Gas solubility and temperature solubility usually decreases with increasing temperature 12.4

15. Pressure and Solubility of Gases 12.5 The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law). c = kP c is the concentration (M) of the dissolved gas P is the pressure of the gas over the solution k is a constant (mol L -1 atm -1 ) that depends only on temperature low P low c high P high c

16. 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. Vapor-Pressure Lowering Raoult’s law 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

17. P A = X A P A 0 P B = X B P B 0 P T = P A + P B P T = X A P A 0 + X B P B 0 Ideal Solution 12.6

18. P T is greater than predicted by Raoults’s law P T is less than predicted by Raoults’s law Force A-B Force A-A Force B-B <& Force A-B Force A-A Force B-B >& 12.6

19. Fractional Distillation Apparatus 12.6

20. 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) 12.6

21. 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) 12.6

23. 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 0 C – 4.48 0 C = -4.48 0 C 12.6

24. 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 solvent molecules. Osmotic pressure (  ) is the pressure required to stop osmosis. dilute more concentrated

25. 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

26. A cell in an: isotonic solution hypotonic solution hypertonic solution 12.6

27. 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

28. Colligative Properties of Electrolyte Solutions 12.6 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

29. 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

30. A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance. Colloid versus solution collodial particles are much larger than solute molecules collodial suspension is not as homogeneous as a solution 12.8

31. The Cleansing Action of Soap 12.8