Solutions and Their Behavior

1. Solutions and Their Behavior Chapter 14 Chapter 14

2. The Solution Process Solution - A homogeneous mixture composed of a solute and a solvent. Solute – The substance which is dissolved. Solvent – The substance which acts as the dissolving medium. Chapter 14

3. Saturated Solutions and Solubility Mole Fraction, Molarity, and Molality Qualitative Terms: Dilute Solution – A solution in which additional solute may be dissolved. Saturated Solution – A solution in which no more solute may be dissolved. Supersaturated Solution – A solution in which more solute is dissolved than in a saturated solution. Solubility - amount of solute required to form a saturated solution. Chapter 14

4. Ways of Expressing Concentration • Definitions: Chapter 14

5. Ways of Expressing Concentration Mole Fraction, Molarity, and Molality Mole Fraction Molarity Chapter 14

6. Ways of Expressing Concentration Mole Fraction, Molarity, and Molality Molality (m) – moles of solute per kilogram of solution Chapter 14

7. The Solution Process Liquids Dissolving in Liquids Miscible liquids - Mix in any proportions. Immiscible liquids - Do not mix. Chapter 14

8. The Solution Process Liquids Dissolving in Liquids • “Like Dissolves Like” • Polar molecules will dissolve in polar solvents. • Non-polar molecules will dissolve in non-polar solvents. Chapter 14

9. The Solution Process Solids Dissolving in Liquids • “Like Dissolves Like” • Still true but less effective (i.e. there are exceptions) • Also, many dissolution processes are endothermic. • A classic example is Ammonium nitrate in water. • A classic exception is Sulfuric acid in water. Chapter 14

10. The Solution Process Heat of Solution • For a solid to dissolve: • Energy must be supplied to separate the ions in the crystal lattice: -DHlattice • Energy is evolved individual items are surrounded by the solvent: DHhydration • DHsolution = (-DHlattice + DHhydration) Chapter 14

11. Factors Affecting Solubility Temperature Effects Chapter 14

12. Factors Affecting 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. Chapter 14

13. Factors Affecting Solubility Pressure Effects Henry’s Law – The solubility of a gas increases in direct proportion to its partial pressure above the solution. Sg - solubility of gas Pg - the partial pressure of the gas kH - Henry’s law constant. Chapter 14

14. Factors Affecting Solubility Temperature Effects Chapter 14

15. Factors Affecting Solubility Temperature Effects • The solubility of a gas is greater in a cold solvent. • The dissolution of a gas in water is an exothermic process. Chapter 14

16. Colligative Properties • Properties of a solution which depend on quantity of solute molecules. • Solutions formed with a nonvolatile solute will: • have lower vapor pressure • lower freezing point • higher boiling point Chapter 14

17. Colligative Properties Boiling-Point Elevation Chapter 14

18. Colligative Properties Raoult’s Law Raoult’s Law – The equilibrium vapor pressure of the solvent over the solution is directly proportional to the mole fraction of the solvent in the solution Psolvent - vapor pressure of the solvent in the solution Psolvent - vapor pressure of the pure solvent solvent - the mole fraction of solvent Chapter 14

19. Colligative Properties Change in Vapor Pressure DPsolvent - vapor pressure of the solvent in the solution Psolvent - vapor pressure of the pure solvent solute - the mole fraction of solute Chapter 14

20. Colligative Properties Boiling-Point Elevation • As the vapor pressure of a solution decreases, the boiling point increases. • Recall, a solvent boils when its’ vapor pressure equals the atmospheric pressure. Chapter 14

21. Colligative Properties Boiling-Point Elevation Kbp - Molal boiling-point elevation constant m – solution molality DTbp – boiling point change Chapter 14

22. Colligative Properties Freezing-Point Depression • Just as the boiling point is raised, the freezing point is lowered. Chapter 14

23. Colligative Properties Freezing-Point Depression Kfp - Molal freezing-point depression constant m – solution molality DTfp – freezing point change Chapter 14

24. Colligative Properties F.Pt. and B.Pt. Change with Ionic Solutes • The previous equations assumed molecular solids • example, sugar (C6H12O6) • Recall that colligative properties are a function of the number of bodies in the solution. Chapter 14

25. Colligative Properties F.Pt. and B.Pt. Change with Ionic Solutes • F. Pt. depression and B. Pt. equations must be modified to account for this. Kbp - Molal boiling-point elevation constant m – solution molality DTbp – boiling point change i – van Hoff factor Chapter 14

26. Colligative Properties F.Pt. and B.Pt. Change with Ionic Solutes Kfp - Molal freezing-point depression constant m – solution molality DTfp – freezing point change i – van Hoff factor Chapter 14

27. Colligative Properties Molar Mass Determination The molar mass (molecular weight) can be determined by observing the freezing point change to a solution in which a know quantity of non-volatile solute has been added. Chapter 14

28. Colligative Properties Osmosis The net movement of solvent through a semi-permeable membrane from a dilute to a concentrated solution. Chapter 14

29. Colligative Properties Osmosis Eventually the pressure difference between the arms stops osmosis. Chapter 14

30. Colligative Properties Osmosis Osmotic pressure() - The pressure required to stop osmosis: c - molarity of the solution R - gas constant (0.08206 L(atm)/mol(K)) T - temperature in Kelvin Chapter 14

31. 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. Chapter 14

32. Colloids • Tyndall effect: ability of a Colloid to scatter light. The beam of light can be seen through the colloid. Chapter 14

33. Homework 4, 8, 23, 28, 38,42, 52 Chapter 14