1. Chapter 13 Properties of Solutions
CHEMISTRY The Central Science 9th Edition
Chapter 13 Properties of Solutions
David P. White
Chapter 13

2. The Solution Process
A solution is a homogeneous mixture of solute (present in smallest amount) and solvent (present in largest amount).
In the process of making solutions with condensed phases, intermolecular forces become rearranged.
Chapter 13

3. Chapter 13

4. Consider NaCl (solute) dissolving in water (solvent)
Chapter 13

5. Chapter 13

6. Chapter 13

7. Energy Changes and Solution Formation
There are three energy steps in forming a solution
separation of solute molecules (H1)
separation of solvent molecules (H2),
formation of solute-solvent interactions (H3)
Chapter 13

8. We define the enthalpy change in the solution process as
Hsoln = H1 + H2 + H3
Hsoln can either be positive or negative depending on the intermolecular forces
Breaking attractive intermolecular forces is always endothermic
Forming attractive intermolecular forces is always exothermic
Chapter 13

9. Chapter 13

10. To determine whether Hsoln is positive or negative, we consider the strengths of all solute-solute and solute-solvent interactions
It is possible to have either H3 > (H1 + H2) or H3 < (H1 + H2)
Chapter 13

11. Chapter 13

12. “Rule”: polar solvents dissolve polar solutes
“Rule”: polar solvents dissolve polar solutes. Non-polar solvents dissolve non-polar solutes
Water in octane: water has strong H-bonds. There are no attractive forces between water and octane to compensate for the H-bonds
Chapter 13

13. Solution Formation, Spontaneity, and Disorder
A spontaneous process occurs without outside intervention. (If leads to greater state of disorder, then process is spontaneous).
When energy of the system decreases the process is spontaneous
Some spontaneous processes do not involve the system moving to a lower energy state (e.g. an endothermic reaction)
Chapter 13

14. Solution Formation, Spontaneity, and Disorder
Chapter 13

15. Saturated Solutions and Solubility
Dissolve: solute + solvent  solution
Crystallization: solution  solute + solvent
Saturation: crystallization and dissolution are in equilibrium
Solubility: amount of solute required to form a saturated solution
Supersaturated: a solution formed when more solute is dissolved than in a saturated solution
Chapter 13

16. Chapter 13

17. Factors Affecting Solubility
Solute-Solvent Interaction
Polar liquids tend to dissolve in polar solvents
Miscible liquids: mix in any proportions
Immiscible liquids: do not mix
Intermolecular forces are important
The number of carbon atoms in a chain affect solubility: the more C atoms the less soluble in water
Chapter 13

18. The number of -OH groups increases solubility in water
Generalization: “like dissolves like”
The more polar bonds in the molecule, the better it dissolves in a polar solvent
The less polar the molecule the less it dissolves in a polar solvent and the better is dissolves in a non-polar solvent
Network solids do not dissolve because the strong intermolecular forces in the solid are not re-established in any solution
Chapter 13

19. Solute-Solvent Interaction
Chapter 13

20. Solute-Solvent Interaction
Chapter 13

21. the higher the pressure, the greater the solubility
Pressure Effects
Solubility of a gas in a liquid is a function of the pressure of the gas
the higher the pressure, the greater the solubility
lower the pressure, the lower the solubility
Chapter 13

22. Pressure Effects
Chapter 13

23. If Sg is the solubility of a gas, k is a constant, and Pg is the partial pressure of a gas, then Henry’s Law gives
Chapter 13

24. As temperature increases, solubility of solids generally increases
Temperature Effects
As temperature increases, solubility of solids generally increases
Sometimes, solubility decreases as temperature increases (e.g. Ce2(SO4)3)
Gases get less soluble as temperature increases
Chapter 13

25. Chapter 13

26. Chapter 13

27. Ways of Expressing Concentration
Mass Percentage, ppm, and ppb
Chapter 13

28. Ways of Expressing Concentration
Mole Fraction, Molarity, and Molality
Chapter 13

29. Chapter 13

30. Colligative Properties
Physical Properties of a solution that depend on the number of solute particles, not the identity of solute particles.
Vapor Pressure lowering
Boiling point elevation
Freezing point depression
Osmosis – net movement of solvent molecules through a semi permeable membrane toward a solution with a greater concentration of solute particles.
Chapter 13

31. Colligative Properties
Colligative properties depend on quantity of solute molecules. (E.g. freezing point depression and melting point elevation.)
Lowering Vapor Pressure
Non-volatile solvents reduce the ability of the surface solvent molecules to escape the liquid.
The amount the vapor pressure lowered depends on the amount of solute.
Chapter 13

32. Lowering Vapor Pressure
Chapter 13

33. Raoult’s Law: PA is the vapor pressure with solution, PA is the vapor pressure of pure solvent, and A is the mole fraction of solvent, then
Chapter 13

34. Lowering Vapor Pressure
Ideal solution: one that obeys Raoult’s law.
Raoult’s law breaks down when the solvent-solvent and solute-solute intermolecular forces are greater than solute-solvent intermolecular forces.
Chapter 13

35. Boiling-Point Elevation
Goal: interpret the phase diagram for a solution.
Non-volatile solute lowers the vapor pressure.
Therefore the triple point - critical point curve is lowered.
Chapter 13

36. Chapter 13

37. Boiling-Point Elevation
Molal boiling-point-elevation constant, Kb, expresses how much Tb changes with molality, m:
Chapter 13

38. Freezing Point Depression
Decrease in freezing point (Tf) is directly proportional to molality (Kf is the molal freezing-point-depression constant):
Chapter 13

39. Freezing Point Depression
Chapter 13

40. Chapter 13

41. Eventually, the pressure difference between the arms stops osmosis.
Chapter 13

42. Osmotic pressure, , is the pressure required to stop osmosis:
Chapter 13

43. Hypotonic solutions: a solution of lower  than a hypertonic solution.
Isotonic solutions: two solutions with the same  separated by a semipermeable membrane.
Hypotonic solutions: a solution of lower  than a hypertonic solution.
Osmosis is spontaneous.
Red blood cells are surrounded by semipermeable membranes.
Chapter 13

44. Crenation:
red blood cells placed in hypertonic solution (relative to intracellular solution);
there is a lower solute concentration in the cell than the surrounding tissue;
osmosis occurs and water passes through the membrane out of the cell.
The cell shrivels up.
Chapter 13

45. Osmosis
Chapter 13

46. Hemolysis:
red blood cells placed in a hypotonic solution;
there is a higher solute concentration in the cell;
osmosis occurs and water moves into the cell.
The cell bursts.
To prevent crenation or hemolysis, IV (intravenous) solutions must be isotonic.
Chapter 13

47. Salty food causes retention of water and swelling of tissues (edema).
Cucumber placed in NaCl solution loses water to shrivel up and become a pickle.
Limp carrot placed in water becomes firm because water enters via osmosis.
Salty food causes retention of water and swelling of tissues (edema).
Water moves into plants through osmosis.
Salt added to meat or sugar to fruit prevents bacterial infection (a bacterium placed on the salt will lose water through osmosis and die).
Chapter 13

48. Active transport is not spontaneous.
Active transport is the movement of nutrients and waste material through a biological system.
Active transport is not spontaneous.
Chapter 13

49. 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.
Particle size: 10 to 2000 Å.
There are several types of colloid:
aerosol (gas + liquid or solid, e.g. fog and smoke),
foam (liquid + gas, e.g. whipped cream),
emulsion (liquid + liquid, e.g. milk),
sol (liquid + solid, e.g. paint)
Chapter 13

50. Tyndall effect: ability of a Colloid to scatter light
Tyndall effect: ability of a Colloid to scatter light. The beam of light can be seen through the colloid.
Chapter 13

51. Chapter 13

52. “Water loving” colloids: hydrophilic.
“Water hating” colloids: hydrophobic.
Molecules arrange themselves so that hydrophobic portions are oriented towards each other
Typical hydrophilic groups are polar (containing C-O, O-H, N-H bonds) or charged
Hydrophobic colloids need to be stabilized in water
Adsorption: when something sticks to a surface we say that it is adsorbed
Chapter 13

53. Chapter 13

54. Hydrophilic and Hydrophobic Colloids
Chapter 13

55. Colloids
Chapter 13

56. Hydrophilic and Hydrophobic Colloids
Most dirt stains on people and clothing are oil-based. Soaps are molecules with long hydrophobic tails and hydrophilic heads that remove dirt by stabilizing the colloid in water.
Bile excretes substances like sodium stereate that forms an emulsion with fats in our small intestine.
Emulsifying agents help form an emulsion.
Chapter 13

57. Colloid particles are too small to be separated by physical means (e.g. filtration)
Colloid particles are coagulated (enlarged) until they can be removed by filtration
Chapter 13

58. End of Chapter 13 Properties of Solutions