1. Tro, Chemistry: A Molecular Approach

2. Physical Properties of Solutions
12.1 Types of Solutions.
12.2 A Molecular View of the Solution Process.
12.3 Concentration Units.
12.4 The Effect of Temperature on Solubility.
12.5 The Effect of Pressure on the Solubility of Gases.
12.6 Colligative Properties of Nonelectrolyte Solutions.
12.7 Colligative Properties of Electrolyte Solutions.
12.8 Colloids.
Tro, Chemistry: A Molecular Approach

3. A LOOK AHEAD
We begin by examining different types of solutions that can be formed from the three states of matter: solid, liquid and gas. We also characterize a solution by the amount of solute present.
Study the formation of solution at the molecular level and see how intermolecular forces affect the energetics of the solution process and solubility.
Study the four major types of concentration units—percent by mass, mole fraction, molarity and molality and their interconversions.
Temperature in general has a marked effect on the solubility of gases as well as liquids and solids.
Tro, Chemistry: A Molecular Approach

4. A LOOK AHEAD
We see that pressure has no influence on the solubility of liquids and solids, but greatly affects the solubility of gases. The quantitative relationship between gas solubility and pressure is given by Henry’s law.
We learn that physical properties such as the vapor pressure, melting point, boiling point and osmotic pressure of a solution depend only on the concentration and not on the identity of the solute present. First we study these colligative properties and their applications for nonelectrolyte solutions.
We learn about the influence of ion pair formation on the colligative properties.
Tro, Chemistry: A Molecular Approach

5. 2.1 Types of Solutions Solutions involving at least one liquid component – that is, gas-liquid, liquid-liquid and solid-liquid solutions. Chemists characterize solutions by their capacity to dissolve a solute.
Tro, Chemistry: A Molecular Approach

6. n
Tro, Chemistry: A Molecular Approach

7. There are three types of solutions: 1- A Saturated Solution, 2- An unsaturated Solution, and 3- A Supersaturated Solution
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8. Tro, Chemistry: A Molecular Approach

9. 12.2 A Molecular View of the Solution Process
When one substance (solute) dissolves in another (solvent), particles of the solute disperse throughout the solvent.
In liquids and solids the intermolecular attractions hold molecules together and it is play a central role in the formation of solutions.

10. The ease with which a solute particle replaces a solvent molecule depends on the relative strengths of interaction. There are three types of interactions: 1- solvent – solvent interaction 2- solute- solute interaction 3- solute- solvent interaction Figure 12.2: show that step 1 is the separation of solvent molecules, and step 2 entails the separation of solute molecules (require energy to break attractive intermolecular forces, they are endothermic). In step 3 the solvent and solute mix (exothermic or endothermic)
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11. The heat of solution ΔH soln
The heat of solution ΔH soln.is given by the relation: ΔH = ΔH1 + ΔH2 + ΔH3
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12. Tro, Chemistry: A Molecular Approach

13. If the solute-solvent attraction is stronger than the solvent-solvent attraction and solute-solute attraction, the solution process is endothermic (ΔHsoln.<0). If the solute-solvent attraction is weaker than the solvent-solvent and solute-solute interaction, then the solution process is endothermic (ΔHsoln.>0). The solution process, like all physical and chemical processes, is governed by two factors: 1- energy (which determines whether a solution process is endothermic or exothermic) , 2- the second factor is an inherent toward disorder .
Tro, Chemistry: A Molecular Approach

14. In the pure state, the solute and solvent process a fair degree of order (arrangement of atoms more or less) and when solute and solvent molecules mix to form a solution, there is an increase in randomness (disorder). Much of this order is destroyed when the solute dissolves in the solvent (see fig. 12.2). We can say that the increase in disorder of the system that favors the solubility of any substance. Solubility is a measure of how much solute will dissolve in a solvent at a specific temperature.
Tro, Chemistry: A Molecular Approach

15. The saying “like dissolves like” means that two substances with intermolecular forces of similar type and magnitude are likely to be soluble in each other. Example: CCl4 and C6H6 are nonpolar liquids and there are dissolves in each other. Two liquids are said to be miscible if they are completely soluble in each other in all proportions., example alcohols are miscible with water because they can form hydrogen bonds with water molecules.
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16. Solvation is the process in which an ion or molecules is surrounded by solvent molecules arranged in a specific manner The process called hydration when the solvent is water. The predominant intermolecular interaction between ions and nonpolar compounds is ion-induced dipole interaction, which is much weaker than ion dipole interaction. Ionic compounds usually have extremely low solubility in nonpolar solvents.
Tro, Chemistry: A Molecular Approach

17. Worked Example 12.1

18. Tro, Chemistry: A Molecular Approach

19. Common units of concentration are:
12.3 Concentration Units
Concentration is the amount of solute present in a given amount of solution.
Common units of concentration are:
1- percent by mass
2- mole fraction
3-molarity
4- molality

20. Tro, Chemistry: A Molecular Approach

21. Worked Example 12.2

22. The mole fraction has no units, because it too is a ratio of two similar quantities. Molarity (M): molarity = moles of solute / liters of solution The units of molarity are mol/L. Molality (m): Molality is the number of moles of solute dissolved in 1 kg (1000g) of solvent. molality = moles of solute / mass of solvent (kg)
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23. For example: when prepare 1 molal (m) of Na2SO4 solution, we need to dissolve 1 mole (142g) of the substance in 1000g (1kg) of water. See Example 12.3 page: 508
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24. Tro, Chemistry: A Molecular Approach

25. Worked Example 12.3

26. Worked Example 12.4

27. Worked Example 12.5

28. 12.4 The Effect of Temperature on Solubility
Temperature affects the solubility of most substance.
Solubility is defined as the maximum amount of a solute that will dissolves in a given quantity at a specific temperature.
There are solid solubility and gas solubility

29. Solid Solubility and Temperature Figure 12
Solid Solubility and Temperature Figure 12.3 page 512 shows the temperature dependent of the solubility of some ionic compounds in water. The difference in solubility between compounds is useful in Fractional crystallization. Fractional crystallization is the separation of a mixture of substances into pure components on the basis of their differing solubility's. Many of solid inorganic and organic compounds that are used in laboratory were purified by fractional crystallization

30. Tro, Chemistry: A Molecular Approach

31. Gas Solubility and Temperature The solubility of gases in water decreases with increasing temperature ( Figure 12.5).
Tro, Chemistry: A Molecular Approach

32. Tro, Chemistry: A Molecular Approach

33. 12.5 The Effect of Pressure on the Solubility of Gases The quantitative relationship between gas solubility and pressure is that the solubility of a gas in a liquid is proportional to the gas over the solution, which called Henry’s law C α P C = k P C is the molar concentration of the dissolved gas (mol/L), P is the pressure in atm. and k is a constant depends on temperature.
Tro, Chemistry: A Molecular Approach

34. Tro, Chemistry: A Molecular Approach

35. See Example 12.6 page 514 Most gas obey Henry’s law, but there are some exceptions. For example: if the dissolved gas react with water, higher solubility's can result. The solubility of ammonia NH3 is higher than expected because of the reaction: NH3 + H2O NH4 + OH
Tro, Chemistry: A Molecular Approach

36. Worked Example 12.6

37. Tro, Chemistry: A Molecular Approach

38. 12.6 Colligative Properties of Nonelectrolyte Solutions.
Colligative properties (or colligative properties) are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. The number of solute particals such as atoms, ions or molecules.
The colligative properties are:
Vapor pressure lowering,
Boiling point elevation,
Freezing point depression and
Osmotic pressure.

39. Discussion of colligative properties of nonelectrolyte it is important to keep in our mind that we are talking about relatively dilute solutions (c less or equal 0.2 M)
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40. Vapor-Pressure Lowering
If a solute is nonvolatile (that is, it does not have a measurable vapor pressure), the vapor pressure of its solution is always less than that of the pure solvent. Thus, the relationship between solution vapor pressure and solvent vapor pressure depends on the concentration of the solute in the solution.

41. Tro, Chemistry: A Molecular Approach

42. From this equation, we see that the decrease in vapor pressure, ΔP, is directly proportional to the solute concentration X2 (which measured in mole fraction). Example 12.7 illustrates the use of Raoult’s law . Q-Why is the vapor pressure of a solution less than that of the pure solvent?
Tro, Chemistry: A Molecular Approach

43. Worked Example 12.7

44. Because a solution is more disordered than a pure solvent, the difference in disorder between a solution and a vapor is less than that between a pure solvent and a vapor. Thus, solvent molecules have less a tendency to leave a solution than to leave the pure solvent to become vapor, and the vapor pressure of a solution is less than that of the solvent. If both components of a solution are volatile , the vapor pressure of the solution is the sum of the individual partial pressures.
Tro, Chemistry: A Molecular Approach

45. Tro, Chemistry: A Molecular Approach

46. Tro, Chemistry: A Molecular Approach

47. Case1) If the intermolecular forces between A and B molecules are weaker than those between A molecules and B molecules, then there is greater tendency for these molecules to leave the solution than in case of an ideal solution. The vapor pressure of the solution is greater than the sum of the vapor pressure. Case 2) If A molecules attract B molecules more strongly than they do their own kind, the vapor pressure of the solution is less than the sum of the vapor pressures as predicted by Raoult’s law.
Tro, Chemistry: A Molecular Approach

48. Tro, Chemistry: A Molecular Approach

49. Boiling –Point Elevation
The boiling point of a solution is the temperature at which its vapor pressure equals the enternal atmospheric pressure. Because the presence of a nonvolatile solute lowers the vapor pressure of a solution , it must also affect the boiling point of the solution.
Figure shows the phase diagram of water and the changes that occur in an aqueous solution.

50. This graphical analysis shows that the boiling point of the solution is higher than that of water. The boiling point elevation (ΔTb) is defined as the boiling point of the solution (Tb) minus the boiling point of the pure solvent (Tb).
Tro, Chemistry: A Molecular Approach

51. Tro, Chemistry: A Molecular Approach

52. The value of ΔTb is proportional to the vapor-pressure lowering, and so it is also proportional to the concentration in molality of the solution: ΔTb α m ΔTb = Kb m where m is the molality of the solution Kb is the molal boiling point elevation.
Tro, Chemistry: A Molecular Approach

53. Freezing-Point Depression Figure 12
Freezing-Point Depression Figure shows that lowering the vapor pressure of the solution shifts the solid liquid curve to the left. Consequently, The freezing point depression (ΔTf) is defend as the freezing point of the pure solvent (Tf) minus the freezing point of the solution (Tf).
Tro, Chemistry: A Molecular Approach

54. Tro, Chemistry: A Molecular Approach

55. Tro, Chemistry: A Molecular Approach

56. Tro, Chemistry: A Molecular Approach

57. Worked Example 12.8

58. Osmotic Pressure (π)
Many chemical and biological processes depend on osmosis, the selective passage of solvent molecules through a porous from a dilute solution to a more concentrated one,(Figure 12.11).

59. Tro, Chemistry: A Molecular Approach

60. Tro, Chemistry: A Molecular Approach

61. The osmotic pressure, π, is expressed in atm
The osmotic pressure, π, is expressed in atm. Because osmotic pressure measurements are carried out at constant temperature, we express the concentration in terms of the more convenient units of molarity rather than molality. Like boiling-point elevation and freezing-point depression, osmotic pressure is directly proportional to the concentration of solution, because all colligative properties depends only on the number of solute partials in a solution.

62. - If two solutions are equal concentration and they have the same osmotic pressure, they are said to be isotonic If two solutions are of unequal concentrations and unequal osmotic pressures, the more concentrated solution is said to be hypertonic and the more dilute solution is described as hypotonic. See Figure 12.13
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63. Tro, Chemistry: A Molecular Approach

64. Worked Example 12.9

65. Using Colligative Properties to Determine Molar Mass
Using Colligative Properties to Determine Molar Mass * Theoretically, any of the four colligative properties is suitable for determining the molar mass. * In practical , only freezing-point depression and osmotic pressure are used to determining the molar mass, because they show the most pronounced changes. By determined freezing point depression or osmotic pressure, we can calculate the molality or molarity of the solution. Knowing the mass of the solute, we can readily determine the molar mass. See examples and 12.11
Tro, Chemistry: A Molecular Approach

66. Worked Example 12.10

67. Worked Example 12.11

68. 12.7 Colligative Properties of Electrolyte Solutions
The colligative properties of electrolyte solutions differed from the colligative properties for nonelectrolyte solutions, because the electrolytes dissociate into ions in solution, and one unit of electrolyte compound separates into two or more particles when it dissolves.

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72. Worked Example 12.12

73. 12.8 Colloids
The solutions are homogeneous mixtures. a heterogeneous mixture such as sand add to a beaker of water and stir, the sand partials are suspended at first but then gradually settle to the bottom. Between these two extremes is an intermediate state called colloidal suspension or a colloid.
Colloid is dispersion of partials of one substance (the dispersed phase) throughout a dispersing medium made of another substance. Colloidal particles are much larger than the normal solute molecules.

74. Hydrophilic and Hydrophobic Colloids
Colloids are divided into two categories:
1- hydrophilic or water-loving, they stable in water and interact favorably with water molecules by ion-dipole forces or hydrogen bond formation.
2- hydrophobic or water fearing, they normally would not be stable in water, and the particles would clump together and they can be stabilized by adsorption of ions on their surface .
Or by the presence of other hydrophilic groups on their surface , such as sodium stearate (C17H35COONa) a soap molecule that has a polar head and a long hydrocarbon tail that is nonpolar, see Figure (12.19)

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76. Tro, Chemistry: A Molecular Approach

77. Soap Action
most dirt and grease is made of nonpolar molecules – making it hard for water to remove it from the surface
soap molecules form micelles around the small oil particles with the polar/ionic heads pointing out
this allows the micelle to be attracted to water and stay suspended
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78. The polar heads of the micelles attract them to the water, and simultaneously repel other micelles so they will not coalesce and settle out.
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