1. 1 Chapter 11: Properties of Solutions Many reactions do not occur until the solid reactants are dissolved to make a solution. Many reactions do not occur until the solid reactants are dissolved to make a solution. A solution is a homogeneous mixture of a solvent and a solute. A solution is a homogeneous mixture of a solvent and a solute. The solvent is the substance present in greater amount. The solvent is the substance present in greater amount. Leadiod.mov

2. 2 Representing Solutions Draw a particle diagram of a solution (mixture) of sodium chloride in water. Draw a particle diagram of a solution (mixture) of sodium chloride in water. Identify the different parts of the solution. Identify the different parts of the solution. How could we describe the amounts of the different parts of solution? How could we describe the amounts of the different parts of solution?

3. 3 Solutions and Solubility Solute: the substance being dissolved; the substance present in lesser amount Solute: the substance being dissolved; the substance present in lesser amount Solvent: the substance doing the dissolving; the substance present in greater amount Solvent: the substance doing the dissolving; the substance present in greater amount Concentration: measure of the relative amounts of substances making up a solution Concentration: measure of the relative amounts of substances making up a solution

4. 4 Ways of Expressing Concentration Qualitative terms relating to solubility Qualitative terms relating to solubility insoluble, slightly soluble, soluble, very soluble insoluble, slightly soluble, soluble, very soluble 2 g/100 g 2 g/100 g Other comparative terms: Other comparative terms: dilute, concentrated dilute, concentrated miscible, immiscible, partially miscible miscible, immiscible, partially miscible Quantitative expressions use ratios Quantitative expressions use ratios Concentration = amount of solute/amount of solvent or solution Concentration = amount of solute/amount of solvent or solution Variety of units Most commonly used is M (molarity) Variety of units Most commonly used is M (molarity)

5. 5 Concentration Units Molarity M = moles solute = mol Molarity M = moles solute = mol Liter solution L Liter solution L Depends on temperature because liquid volumes change with temperature Depends on temperature because liquid volumes change with temperature Molality Molality m = moles solute = mol m = moles solute = mol kilograms solvent kg kilograms solvent kg Independent of temperature because masses do not change with temperature Independent of temperature because masses do not change with temperature

6. 6 Concentration Units Mass percent Mass percent (mass of solute / mass of solution) * 100% independent of temperature use density to determine masses Mole fraction Mole fraction calculated per component of solution: moles of A / total moles of all components expressed as a decimal (fraction)

7. 7 Concentration Units Difference between molarity and molality

8. 8 11.1-2 The Solution Process During dissolution, existing forces are broken and new forces are created. During dissolution, existing forces are broken and new forces are created. Figure 11.4 disolve7 Vd13_001

9. 9 The Solution Process The forces involved in solutions are the bonding and intermolecular forces discussed earlier.

10. 10 Hydration Hydration (solvation) of cations and anions makes new forces. Hydration (solvation) of cations and anions makes new forces.  H solvation is the energy for the process: solute(g) + solvent(g)  solvated solute particles  H solvation is the energy for the process: solute(g) + solvent(g)  solvated solute particles 13m04an1

11. 11 Energy Changes and Solution Formation We define the enthalpy change in the solution process as We define the enthalpy change in the solution process as  H soln =  H 1 +  H 2 +  H 3.  H soln can either be positive or negative depending on the intermolecular forces.  H soln can either be positive or negative depending on the intermolecular forces.

12. 12 Heat of Solution Old forces to be broken: lattice energy of an ionic solute and intermolecular forces (IMF) of a liquid Old forces to be broken: lattice energy of an ionic solute and intermolecular forces (IMF) of a liquid New forces take hold:  H solvation, which increases with increasing charge and decreasing size of an ion New forces take hold:  H solvation, which increases with increasing charge and decreasing size of an ion Heat of solution can be found by comparison Heat of solution can be found by comparison

13. 13 Endothermic Solution Process If the heat of solution has a positive value (>0), the solution is less stable than the separated solute and solvent. If the heat of solution has a positive value (>0), the solution is less stable than the separated solute and solvent. Figure 11.2

14. 14 Exothermic Solution Process If the heat of solution has a negative value (<0), the solution is more stable than the separated solute and solvent. If the heat of solution has a negative value (<0), the solution is more stable than the separated solute and solvent. Figure 11.2

15. 15 Heat of Solution  H solution is the energy for the process: solute + solvent  solution  H solution is the energy for the process: solute + solvent  solution Can analyze as a three-step process. (Hess’s Law) Can analyze as a three-step process. (Hess’s Law)

16. 16 Solution Process Processes tend to occur spontaneously if they lead to a lower energy (enthalpy) or to an increased randomness or disorder (entropy). Processes tend to occur spontaneously if they lead to a lower energy (enthalpy) or to an increased randomness or disorder (entropy). Why does an exothermic solution process occur? Why does an exothermic solution process occur? Why does an endothermic solution process occur? Why does an endothermic solution process occur?

17. 17 Solubility of Solutes Unsaturated solution: less than the maximum amount of solute is dissolved Unsaturated solution: less than the maximum amount of solute is dissolved 14m02vd2

18. 18 Solubility Solubility: the maximum amount of solute in a given amount of solution Solubility: the maximum amount of solute in a given amount of solution Saturated solution: an equilibrium situation in which the maximum amount of solute is dissolved in a given amount of solvent Saturated solution: an equilibrium situation in which the maximum amount of solute is dissolved in a given amount of solvent 14m02vd1

19. 19 Solubility Supersaturated solution: more than the maximum amount of solute is dissolved; an unstable state that reverts to a saturated solution if the solution is disturbed in some way Supersaturated solution: more than the maximum amount of solute is dissolved; an unstable state that reverts to a saturated solution if the solution is disturbed in some way Acetate_supersaturate.movsupersat.mov

20. 20 11.3 Factors Affecting Solubility What causes different solubilities? What factors might affect solubility? What causes different solubilities? What factors might affect solubility? General Rule: “Like dissolves like” General Rule: “Like dissolves like” The definition of “like” involves the nature of the bonding and structure of solute and solvent: ionic or polar covalent vs. non- polar covalent. The definition of “like” involves the nature of the bonding and structure of solute and solvent: ionic or polar covalent vs. non- polar covalent.

21. 21 Effect of Molecular Structure on Solubility Non-polar liquids, like C 6 H 6 (benzene) and CCl 4, dissolve readily in other non-polar liquids, but not very readily in polar liquids. Non-polar liquids, like C 6 H 6 (benzene) and CCl 4, dissolve readily in other non-polar liquids, but not very readily in polar liquids. Polar liquids, like HO-CH 2 -CH 2 -OH (ethylene glycol) and H 2 O, dissolve readily in other polar liquids, but not very readily in non-polar liquids. Polar liquids, like HO-CH 2 -CH 2 -OH (ethylene glycol) and H 2 O, dissolve readily in other polar liquids, but not very readily in non-polar liquids. Why is this the case? Hint: Analyze the solution process in terms of forces made and broken. Why is this the case? Hint: Analyze the solution process in terms of forces made and broken.

22. 22 Effect of Temperature on Solubility Most, but not all, ionic solids are more soluble at higher temperatures. Most, but not all, ionic solids are more soluble at higher temperatures.

23. 23 Effect of Temperature on Solubility Endothermic solution process: added heat at higher temperatures helps overcome the intermolecular forces, so solubility increases with increased temperature. Endothermic solution process: added heat at higher temperatures helps overcome the intermolecular forces, so solubility increases with increased temperature. Exothermic solution process: added heat overcomes solute- solvent forces, so solubility decreases with increased temperature. Exothermic solution process: added heat overcomes solute- solvent forces, so solubility decreases with increased temperature.

24. 24 Solubility of Gases Most gases are only slightly soluble in water. Exceptions are HCl and NH 3. Most gases are only slightly soluble in water. Exceptions are HCl and NH 3. Why are these molecules unusually soluble? Why are these molecules unusually soluble? Figure 11.8 Ammonia Fountain

25. 25 Solubility of Gases Pressure can effect gases dissolved in liquids. Pressure can effect gases dissolved in liquids. How does pressure affect the solubility equilibrium? How does pressure affect the solubility equilibrium?

26. 26 Effect of Pressure on Gas Solubility Expressed Mathematically: Expressed Mathematically: Henry’s Law: C = k P Why does a soft drink fizz when the container is opened? Why does a soft drink fizz when the container is opened? Why are patients with breathing difficulties placed in an oxygen tent? Why are patients with breathing difficulties placed in an oxygen tent? 14s05vd1

27. 27 Effect of Temperature on Gas Solubility How does gas solubility change with temperature? How does gas solubility change with temperature? When would the solubility of the gas become zero? When would the solubility of the gas become zero? Why does the taste of water change if it is boiled? Why does the taste of water change if it is boiled?

28. 28 Colligative Properties [11.4 – 11.7] Colligative properties are those whose value depends only on the concentration of dissolved particles, not on their identity. The particles may be molecules or ions. If they are ions, the important factor is the sum of the concentrations of cations and anions. Colligative properties are those whose value depends only on the concentration of dissolved particles, not on their identity. The particles may be molecules or ions. If they are ions, the important factor is the sum of the concentrations of cations and anions. Examples: vapor pressure boiling point melting point osmotic pressure Examples: vapor pressure boiling point melting point osmotic pressure

29. 29 11.4 Vapor Pressure P vap of a solution < P vap of the solvent P vap of a solution < P vap of the solvent Evidence: solvent evaporates from a less concentrated solution and condenses into a more concentrated solution in a closed container. Figure 11.16 Evidence: solvent evaporates from a less concentrated solution and condenses into a more concentrated solution in a closed container. Figure 11.16 14m07an114m07an2

30. 30 11.4 Vapor Pressure P vap is lowered because fewer surface positions are occupied by solvent molecules and because intermolecular forces in solutions are usually greater than those in the separated substances. P vap is lowered because fewer surface positions are occupied by solvent molecules and because intermolecular forces in solutions are usually greater than those in the separated substances.

31. 31 The extent to which a non volatile solute lowers the vapor pressure is proportional to its concentration. This relationship is expressed by Raoult's law, which states that the partial pressure exerted by solvent vapor above a solution, P A,equals the product of the mole fraction of the solvent in the solution,X A,times the vapor pressure of the pure solvent: P A = X A P A o

32. 32 11.4 Vapor Pressure The lowering of vapor pressure can also be seen on a phase diagram. The lowering of vapor pressure can also be seen on a phase diagram.

33. 33 11.5 Freezing Point Depression Boiling Point Elevation Note on phase diagram that the freezing point decreases and the boiling point increases for a solution, as a result of the lowering of the vapor pressure. Note on phase diagram that the freezing point decreases and the boiling point increases for a solution, as a result of the lowering of the vapor pressure. 14m08an214m08an3

34. 34 Equations that describe these effects:  T f = i K f m  T b = i K b m Equations that describe these effects:  T f = i K f m  T b = i K b m  T is the magnitude of the temperature change m = moles solute/kg solvent (independent of T!) i = number of particles per formula unit (van’t Hoff factor, see section 11.7)  T is the magnitude of the temperature change m = moles solute/kg solvent (independent of T!) i = number of particles per formula unit (van’t Hoff factor, see section 11.7) K is determined by the identity of the solvent and does NOT depend on the solute! http://chemistry.about.com/cs/howthingswork/a/aa 120703a.htm http://chemistry.about.com/cs/howthingswork/a/aa 120703a.htm Freezing Point Depression Boiling Point Elevation

35. 35 How many particles per formula unit? CH 3 OH CH 3 OH NaCl NaCl C 6 H 12 O 6 C 6 H 12 O 6 CuCl 2 CuCl 2 CH 2 Cl 2 CH 2 Cl 2 Na 3 PO 4 Na 3 PO 4 NH 4 Cl NH 4 Cl

36. 36 Applications of  T antifreeze and “antiboil” antifreeze and “antiboil” ice cream makers ice cream makers CaCl 2 on icy roads and in aqueous slurries in winter CaCl 2 on icy roads and in aqueous slurries in winter measuring molar masses measuring molar masses distinguish between electrolytes and non- electrolytes distinguish between electrolytes and non- electrolytes

37. 37 Practice Question 1 Determine the freezing point of a 0.050 m MgCl 2 (aq) solution. Determine the freezing point of a 0.050 m MgCl 2 (aq) solution. Reminders: Reminders:  T f = i K f m  T b = i K b m For the solvent water: For the solvent water: K f = 1.86 o C/m (or units o C * kg/mol) K f = 1.86 o C/m (or units o C * kg/mol) K b = 0.51 o C/m (or units o C * kg/mol) K b = 0.51 o C/m (or units o C * kg/mol)

38. 38 Practice Question 2 A solution of an unknown, non-electrolyte compound was prepared by dissolving 18.00 g of the compound in 150.0 g of water. The resulting solution was found to have a boiling point of 100.34 o C. Calculate the molar mass of the unknown compound. A solution of an unknown, non-electrolyte compound was prepared by dissolving 18.00 g of the compound in 150.0 g of water. The resulting solution was found to have a boiling point of 100.34 o C. Calculate the molar mass of the unknown compound. If the empirical formula of the compound is CH 2 O, what is the molecular formula? If the empirical formula of the compound is CH 2 O, what is the molecular formula?  T b = i K b m, for water K b = 0.51 o C/m

39. 39 Practice Question 3 Consider the following solutions: Consider the following solutions: pure water pure water 0.010 m C6H12O6 in water 0.010 m C6H12O6 in water 0.020 m NaCl in water 0.020 m NaCl in water 0.020 m Na 2 SO 4 in water 0.020 m Na 2 SO 4 in water Choose the solution with the: Choose the solution with the: Highest vapor pressure? Lowest vapor pressure? Highest vapor pressure? Lowest vapor pressure? Highest freezing point? Lowest freezing point? Highest freezing point? Lowest freezing point? Highest boiling point? Lowest boiling point? Highest boiling point? Lowest boiling point?

40. 40 11.6 Osmosis Solvent molecules move through a semipermeable membrane from a dilute solution to a concentrated solution; solute cannot move through the membrane. Figure 11.19 Solvent molecules move through a semipermeable membrane from a dilute solution to a concentrated solution; solute cannot move through the membrane. Figure 11.19 14m09an114m09an314m09an2

41. 41 11.6 Osmotic Pressure Another Equilibrium Effect! Another Equilibrium Effect! If solutions have equal concentrations, solvent continues to move in both directions at equal rates. The movement of solvent creates a pressure that opposes additional net movement. If solutions have equal concentrations, solvent continues to move in both directions at equal rates. The movement of solvent creates a pressure that opposes additional net movement. osmotic_pressure.exe

42. 42 11.6 Osmotic Pressure

43. 43 Osmotic pressure (  ) follows an equation much like the ideal gas law:  V = n R T or  = M R Tor  = i M R T Osmotic pressure (  ) follows an equation much like the ideal gas law:  V = n R T or  = M R Tor  = i M R T R = 0.08206 L atm/mol K M = concentration of particles (molecules or ions) in mol/L R = 0.08206 L atm/mol K M = concentration of particles (molecules or ions) in mol/L Easy to measure small , so useful for determining molar masses of large molecules like proteins and polymers. Easy to measure small , so useful for determining molar masses of large molecules like proteins and polymers.

44. 44 Applications of Osmosis Why does lettuce become crispy when soaked in water? Why does lettuce become crispy when soaked in water? Why do prunes expand when soaked in water? Why do prunes expand when soaked in water? Blood cells were soaked in water, 5% glucose, and 25% glucose. Identify the blood cell that received each treatment. Figure 11.21c Blood cells were soaked in water, 5% glucose, and 25% glucose. Identify the blood cell that received each treatment. Figure 11.21c

45. 45 Blood Cells Why is D5W administered by paramedics to trauma victims? onion_1M_nacl

46. 46 Osmosis in Onion Cells Onion cells shrink when placed in 1 M NaCl. Onion cells shrink when placed in 1 M NaCl.

47. 47 11.8 Colloids Colloids are suspensions in which the suspended particles are larger than molecules but too small to drop out of the suspension due to gravity. Colloids are suspensions in which the suspended particles are larger than molecules but too small to drop out of the suspension due to gravity. Particle size: 10 to 2000 Å (1 to 1000 nm) Particle size: 10 to 2000 Å (1 to 1000 nm) Can be detected by the Tyndall effect Can be detected by the Tyndall effect Scattering of light due to the suspended particles Scattering of light due to the suspended particles

48. 48 Tyndall Effect

49. 49 Colloids There are several types of colloid (table 11.7): There are several types of colloid (table 11.7): aerosol (gas + liquid or solid, e.g. fog and smoke), aerosol (gas + liquid or solid, e.g. fog and smoke), foam (liquid + gas, e.g. whipped cream), foam (liquid + gas, e.g. whipped cream), emulsion (liquid + liquid, e.g. milk), emulsion (liquid + liquid, e.g. milk), sol (liquid + solid, e.g. paint), sol (liquid + solid, e.g. paint), solid foam (solid + gas, e.g. marshmallow), solid foam (solid + gas, e.g. marshmallow), solid emulsion (solid + liquid, e.g. butter), solid emulsion (solid + liquid, e.g. butter), solid sol (solid + solid, e.g. ruby glass). solid sol (solid + solid, e.g. ruby glass).