1. Chapter 11 Properties of Solutions

2. Chapter 11 Table of Contents Copyright © Cengage Learning. All rights reserved 2 11.1 Solution Composition 11.2 The Energies of Solution Formation 11.3 Factors Affecting Solubility 11.4 The Vapor Pressures of Solutions 11.5 Boiling-Point Elevation and Freezing-Point Depression 11.6Osmotic Pressure 11.7Colligative Properties of Electrolyte Solutions 11.8Colloids

3. Section 11.1 Solution Composition Return to TOC Copyright © Cengage Learning. All rights reserved 3 Various Types of Solutions Example State of SolutionState of Solute State of Solvent Air, natural gasGas Vodka, antifreezeLiquid BrassSolid Carbonated water (soda)LiquidGasLiquid Seawater, sugar solutionLiquidSolidLiquid Hydrogen in platinumSolidGasSolid

4. Section 11.1 Solution Composition Return to TOC Copyright © Cengage Learning. All rights reserved 4 Solution Composition

5. Section 11.2 Atomic MassesThe Energies of Solution Formation Return to TOC Copyright © Cengage Learning. All rights reserved 5 Steps in the Dissolving Process exothermic endothermic

6. Section 11.2 Atomic MassesThe Energies of Solution Formation Return to TOC Copyright © Cengage Learning. All rights reserved 6 Enthalpy (Heat) of Solution Enthalpy change associated with the formation of the solution is the sum of the ΔH values for the steps: ΔH soln = ΔH 1 + ΔH 2 + ΔH 3 ΔH soln may have a positive sign (energy absorbed) or a negative sign (energy released).

7. Section 11.2 Atomic MassesThe Energies of Solution Formation Return to TOC Copyright © Cengage Learning. All rights reserved 7 Enthalpy (Heat) of Solution

8. Section 11.2 Atomic MassesThe Energies of Solution Formation Return to TOC Copyright © Cengage Learning. All rights reserved 8 Concept Check Explain why water and oil (a long chain hydrocarbon) do not mix. In your explanation, be sure to address how ΔH plays a role.

9. Section 11.2 Atomic MassesThe Energies of Solution Formation Return to TOC Copyright © Cengage Learning. All rights reserved 9 The Energy Terms for Various Types of Solutes and Solvents H1H1 H2H2 H3H3  H soln Outcome Polar solute, polar solventLarge Large, negativeSmallSolution forms Nonpolar solute, polar solventSmallLargeSmallLarge, positiveNo solution forms Nonpolar solute, nonpolar solvent Small Solution forms Polar solute, nonpolar solventLargeSmall Large, positiveNo solution forms

10. Section 11.2 Atomic MassesThe Energies of Solution Formation Return to TOC Copyright © Cengage Learning. All rights reserved 10 In General One factor that favors a process is an increase in probability of the state when the solute and solvent are mixed. Processes that require large amounts of energy tend not to occur. Overall, remember that “like dissolves like”.

11. Section 11.3 The MoleFactors Affecting Solubility Return to TOC Copyright © Cengage Learning. All rights reserved 11 Structural Effects:  Polarity Pressure Effects:  Henry’s law Temperature Effects:  Affecting aqueous solutions

12. Section 11.3 The MoleFactors Affecting Solubility Return to TOC Copyright © Cengage Learning. All rights reserved 12 Pressure Effects Henry’s law:C = kP C = concentration of dissolved gas k = constant P =partial pressure of gas solute above the solution Amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

13. Section 11.3 The MoleFactors Affecting Solubility Return to TOC Copyright © Cengage Learning. All rights reserved 13 A Gaseous Solute

14. Section 11.3 The MoleFactors Affecting Solubility Return to TOC Copyright © Cengage Learning. All rights reserved 14 Temperature Effects (for Aqueous Solutions) Although the solubility of most solids in water increases with temperature, the solubilities of some substances decrease with increasing temperature. Predicting temperature dependence of solubility is very difficult. Solubility of a gas in solvent typically decreases with increasing temperature.

15. Section 11.3 The MoleFactors Affecting Solubility Return to TOC Copyright © Cengage Learning. All rights reserved 15 The Solubilities of Several Solids as a Function of Temperature

16. Section 11.3 The MoleFactors Affecting Solubility Return to TOC Copyright © Cengage Learning. All rights reserved 16 The Solubilities of Several Gases in Water

17. Section 11.4 The Vapor Pressures of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 17 An Aqueous Solution and Pure Water in a Closed Environment

18. Section 11.4 The Vapor Pressures of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 18 Vapor Pressures of Solutions Nonvolatile solute lowers the vapor pressure of a solvent. Raoult’s Law: P soln =observed vapor pressure of solution solv =mole fraction of solvent =vapor pressure of pure solvent

19. Section 11.4 The Vapor Pressures of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 19 A Solution Obeying Raoult’s Law

20. Section 11.4 The Vapor Pressures of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 20 Nonideal Solutions Liquid-liquid solutions where both components are volatile. Modified Raoult’s Law: Nonideal solutions behave ideally as the mole fractions approach 0 and 1.

21. Section 11.4 The Vapor Pressures of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 21 Vapor Pressure for a Solution of Two Volatile Liquids

22. Section 11.4 The Vapor Pressures of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 22 Summary of the Behavior of Various Types of Solutions Interactive Forces Between Solute (A) and Solvent (B) Particles  H soln  T for Solution Formation Deviation from Raoult’s Law Example A  A, B  B  A  B Zero None (ideal solution) Benzene- toluene A  A, B  B < A  B Negative (exothermic) PositiveNegative Acetone- water A  A, B  B > A  B Positive (endothermic) NegativePositive Ethanol- hexane

23. Section 11.4 The Vapor Pressures of Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 23 Concept Check For each of the following solutions, would you expect it to be relatively ideal (with respect to Raoult’s Law), show a positive deviation, or show a negative deviation? a)Hexane (C 6 H 14 ) and chloroform (CHCl 3 ) b)Ethyl alcohol (C 2 H 5 OH) and water c)Hexane (C 6 H 14 ) and octane (C 8 H 18 )

24. Section 11.5 Boiling-Point Elevation and Freezing-Point Depression Return to TOC Copyright © Cengage Learning. All rights reserved 24 Depend only on the number, not on the identity, of the solute particles in an ideal solution:  Boiling-point elevation  Freezing-point depression  Osmotic pressure Colligative Properties

25. Section 11.5 Boiling-Point Elevation and Freezing-Point Depression Return to TOC Copyright © Cengage Learning. All rights reserved 25 Nonvolatile solute elevates the boiling point of the solvent. ΔT = K b m solute ΔT = boiling-point elevation K b = molal boiling-point elevation constant m solute = molality of solute Boiling-Point Elevation

26. Section 11.5 Boiling-Point Elevation and Freezing-Point Depression Return to TOC Copyright © Cengage Learning. All rights reserved 26 When a solute is dissolved in a solvent, the freezing point of the solution is lower than that of the pure solvent. ΔT = K f m solute ΔT = freezing-point depression K f = molal freezing-point depression constant m solute = molality of solute Freezing-Point Depression

27. Section 11.5 Boiling-Point Elevation and Freezing-Point Depression Return to TOC Copyright © Cengage Learning. All rights reserved 27 Changes in Boiling Point and Freezing Point of Water

28. Section 11.6 Osmotic Pressure Return to TOC Copyright © Cengage Learning. All rights reserved 28 Osmosis – flow of solvent into the solution through a semipermeable membrane. = MRT =osmotic pressure (atm) M=molarity of the solution R= gas law constant T=temperature (Kelvin)

29. Section 11.6 Osmotic Pressure Return to TOC Copyright © Cengage Learning. All rights reserved 29

30. Section 11.6 Osmotic Pressure Return to TOC Copyright © Cengage Learning. All rights reserved 30

31. Section 11.7 Colligative Properties of Electrolyte Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 31 The relationship between the moles of solute dissolved and the moles of particles in solution is usually expressed as: van’t Hoff Factor, i

32. Section 11.7 Colligative Properties of Electrolyte Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 32 Ion Pairing At a given instant a small percentage of the sodium and chloride ions are paired and thus count as a single particle.

33. Section 11.7 Colligative Properties of Electrolyte Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 33 The expected value for i can be determined for a salt by noting the number of ions per formula unit (assuming complete dissociation and that ion pairing does not occur).  NaCli = 2  KNO 3 i = 2  Na 3 PO 4 i = 4 Examples

34. Section 11.7 Colligative Properties of Electrolyte Solutions Return to TOC Copyright © Cengage Learning. All rights reserved 34 Ion pairing is most important in concentrated solutions. As the solution becomes more dilute, the ions are farther apart and less ion pairing occurs. Ion pairing occurs to some extent in all electrolyte solutions. Ion pairing is most important for highly charged ions. Ion Pairing