1. Solutions

2. Occur in all phases u The solvent does the dissolving. u The solute is dissolved. u We will focus on aqueous solutions.

3. Ways of Measuring u Molarity = moles of solute Liters of solvent u % mass = Mass of solute x 100 Mass of solution  Mole fraction of component A  A = N A N A + N B

4. u Molality = moles of solute Kilograms of solvent  Molality is abbreviated m Ways of Measuring

5. Energy of Making Solutions  Heat of solution (  H soln ) is the energy change for making a solution. u Most easily understood if broken into steps. u 1.Break apart solvent u 2.Break apart solute u 3. Mixing solvent and solute

6. 1. Break apart Solvent  Have to overcome attractive forces.  H 1 >0 2. Break apart Solute.  Have to overcome attractive forces.  H 2 >0

7. Structure and Solubility u Water soluble molecules must have dipole moments - polar bonds. u To be soluble in non polar solvents the molecules must be non polar. u Read section 11.3 – structure effects! pg. 492

8. Soap PO-O- CH 3 CH 2 O-O- O-O-

9. Soap u Hydrophobic non- polar end PO-O- CH 3 CH 2 O-O- O-O-

10. Soap u Hydrophilic polar end PO-O- CH 3 CH 2 O-O- O-O-

11. u A drop of grease in water u Grease is non-polar u Water is polar u Soap lets you dissolve the non-polar in the polar.

12. Hydrophobic ends dissolve in grease

13. Hydrophilic ends dissolve in water

14. u Water molecules can surround and dissolve grease. u Helps get grease out of your way.

15. Pressure effects u Changing the pressure doesn’t effect the amount of solid or liquid that dissolves u They are incompressible. u It does effect gases.

16. Dissolving Gases u Pressure effects the amount of gas that can dissolve in a liquid. u The dissolved gas is at equilibrium with the gas above the liquid.

17. u The gas is at equilibrium with the dissolved gas in this solution. u The equilibrium is dynamic.

18. u If you increase the pressure the gas molecules dissolve faster. u The equilibrium is disturbed.

19. u The system reaches a new equilibrium with more gas dissolved. u Henry’s Law. C= kP

20. Temperature Effects u Increased temperature increases the RATE at which a solid dissolves. u We can’t predict whether it will increase the AMOUNT of solid that dissolves. u We must read it from a graph of experimental data.

21. 20 406080 10 0

22. Gases are predictable u As temperature increases, solubility decreases. u Gas molecules can move fast enough to escape. u Thermal pollution.

23. Vapor Pressure of Solutions u A nonvolatile solvent lowers the vapor pressure of the solution. u The molecules of the solvent must overcome the force of both the other solvent molecules and the solute molecules.

24. Raoult’s Law:  P soln =  solvent x P solvent u Vapor pressure of the solution = mole fraction of solvent x vapor pressure of the pure solvent u Vapor pressure of a solution is directly proportional to the mole fraction of solvent present.

25. Aqueous Solution Pure water u Water has a higher vapor pressure than a solution

26. Aqueous Solution Pure water u Water evaporates faster from the water than solution

27. u The water condenses faster in the solution so it should all end up there. Aqueous Solution Pure water

28. u Calculate the expected vapor pressure at 25oC for a solution prepared by dissolving 158.0g of common table sugar (molar mass = 342.3g/mol) in 643.5 cm3 of water. At 25oC, the density of water is 0.9971 g/mL and a vapor pressure in 23.76 torr. Review Question

29. Colligative Properties u Because dissolved particles affect vapor pressure - they affect phase changes. u Colligative properties depend only on the number - not the kind of solute particles present u Useful for determining molar mass

30. Boiling point Elevation u Because a non-volatile solute lowers the vapor pressure it raises the boiling point.  The equation is:  T = K b m solute   T is the change in the boiling point u K b is a constant determined by the solvent.  m solute is the molality of the solute

31. Freezing point Depression u Because a non-volatile solute lowers the vapor pressure of the solution it lowers the freezing point.  The equation is:  T = K f m solute   T is the change in the freezing point u K f is a constant determined by the solvent  m solute is the molality of the solute

32. 1 atm Vapor Pressure of solution Vapor Pressure of pure water

33. 1 atm Freezing and boiling points of water

34. 1 atm Freezing and boiling points of solution

35. 1 atm TfTf TbTb

36. Electrolytes in solution u Since colligative properties only depend on the number of molecules. u Ionic compounds should have a bigger effect. u When they dissolve they dissociate. u Individual Na and Cl ions fall apart. u 1 mole of NaCl makes 2 moles of ions. u 1mole Al(NO 3 ) 3 makes 4 moles ions.

37. u Electrolytes have a bigger impact on on melting and freezing points per mole because they make more pieces.