1 / 38

Colligative Properties of Solutions

Learn about the colligative properties of solutions, including vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. Discover how to calculate these properties using mole fraction, molality, and the appropriate constants. Email Ken Rogers at kenrogers2@aol.com for a PowerPoint presentation.

bowlesm
Download Presentation

Colligative Properties of Solutions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Office XP To be viewed with PowerPoint. Animation doesn’t work otherwise. Ken Rogers kenrogers2@aol.com

  2. Colligative Properties of Solutions Ken Rogers Miami Killian

  3. Colligative Properties of Solutions Ken Rogers Miami Killian

  4. Colligative Properties of Solutions Physical properties that depend on the # of solute particles • Vapor pressure lowering • Boiling point elevation • Freezing point depression • Osmotic pressure

  5. Vapor pressure of solution Mole fraction of solvent Vapor pressure of solvent 1. Vapor Pressure Lowering (Raoult’s Law)

  6. 20oC 3 mole H2O = 0.75 3 mole H2O + 1 mole sugar For example suppose you had a solution that contained 3 moles of water and 1 mole sugar. Then the mole fraction of solvent would be Pure water at 20oC has a vapor pressure of 17.5 mm Hg 17.5 mm Hg

  7. ? mm Hg But adding a solute to the water blocks the ability of the solvent (water) to vaporize. 17.5 mm Hg PA = ?

  8. 17.5 mm Hg 13 mm Hg

  9. Change in vapor pressure of solution Mole fraction of solute Vapor pressure of solvent Another way of solving this problem is to realize the solution is 25% sugar. So the vapor pressure of the water is going to be lowered by 25%

  10. Change in vapor pressure of solution Vapor pressure of solution Mole fraction of solute Mole fraction of solvent Vapor pressure of solvent Vapor pressure of solvent Look at both ways together….

  11. At 63.5oC vapor pressure of H2O is 175 torr vapor pressure of C2H5OH is 400 torr (more volatile) A solution is made by mixing 100g of H2O and 100g C2H5OH a) What is the mole fraction of ethanol? 100 g H2O = 5.56 mole 100 g C2H5OH = 2.17 mole

  12. What is the ethanol vapor pressure? Pethanol= Xethanol Po Total pressure of both vapors: Pethanol= 0.28 . 400 torr Pethanol= 112 torr 112 torr +126 torr 238 torr c) What is the water vapor pressure? Pwater = Xwater Po Pwater = 0.72 . 175 torr Pwater = 126 torr

  13. 2. Boiling Point Elevation

  14. Water Vapor Pressure Temperature (oC) Pressure (mm Hg) 0.0 4.6 5.0 6.5 10.0 9.2 15.0 12.8 20.0 17.5 25.0 23.8 30.0 31.8 35.0 42.2 40.0 55.3

  15. Any liquid boils when its vapor pressure equals atmospheric pressure 760 mm Hg Vapor Pressure Adding a solute lowers the vapor pressure Vapor pressure of water Vapor pressure of 1m Solution 100oC Temperature

  16. DT 760 mm Hg Vapor Pressure What’s the boiling point of the solution? Vapor pressure of water Vapor pressure of 1m Solution 100oC Temperature DT

  17. The boiling point of a solution is always higher than the pure solvent. Dissolving anything in water raises the b. p. of the water (aqueous) solution. Dissolving anything in alcohol raises the b. p. of the alcohol solution. And the more concentrated the solution, the more the boiling point is raised.

  18. DT 760 mm Hg Vapor Pressure Vapor pressure of 2m Solution DT 100oC Temperature

  19. # of ions produced by electrolyte DTb = kb.m.i molality of the solution the change in the boiling point of the solution molal boiling point constant for water it’s 0.52oC/m

  20. A typical boiling point of solution question: What’s the b. p. of a 2.0m nonelectrolyte aqueous solution? DTb = kb . m . i =0.52oC/m . 2m . 1 =1.04oC Tb =100o + 1.04oC Tb =101.04oC

  21. DT=1.04oC 760 mm Hg Vapor Pressure What’s the boiling point of the solution? Vapor pressure of water Vapor pressure of 2m Nonelectrolyte 100oC Temperature 101.04oC

  22. If the solution was an electrolyte: What’s the b. p. of a 2.0m CaCl2 aqueous solution? CaCl2a Ca+2 + 2Cl-1 i = 3 DTb = kb. m . i = 0.52oC/m . 2m . 3 =3.12o Tb =100o + 3.12o Tb =103.12oC

  23. 3.12oC 760 mm Hg Vapor Pressure Vapor pressure of 2m CaCl2 100oC 103.12oC Temperature

  24. Boiling point of a 1m nonelectrolyte solution with benzene as the solvent? DTb = kb. m . i = 2.53oC/m . 1m . 1 =2.53o Tb =80.1o + 2.53o Tb =82.63oC

  25. 3. Freezing Point Depression

  26. As in the boiling point elevation, the freezing point also changes when a solute is added to a solvent. The solute particles interfere with the ability of the solvent to freeze. The solution has a lower freezing point. In the case of water, which normally freezes at 0oC, an aqueous solution will freeze below 0oC. We’re talking negative numbers here.

  27. The more concentrated the solution, the lower the freezing point. So the equation is similar to the boiling point elevation equation. # of ions produced by electrolyte DTf = kf . m . i molality of the solution the change in the freezing point of the solution molal freezing point constant for water, 1.86oC/m

  28. For that same solution that boiled at 103.12oC: What’s the f. p. of a 2.0m CaCl2 aqueous solution? CaCl2a Ca+2 + 2Cl-1 i = 3 DTf = kf . m . i =1.86oC/m . 2m . 3 = 11.16oC Tf = 0oC - 11.16oC Tf = -11.16oC

  29. Freezing point of a 1m nonelectrolyte solution with chloroform as the solvent? DTf = kf. m . i = 4.68oC/m . 1m . 1 =4.68o Tb = -63.5o – 4.68o Tb = -68.18oC

  30. 4. Osmotic Pressure

  31. pure solvent concentrated solution Osmosis is the spontaneous process of water diffusing through a membrane to the more concentrated solution. semipermeable membrane glass tube

  32. Osmotic pressure is the pressure needed to stop osmosis.

  33. The equation to calculate the pressure needed to stop osmosis (osmotic pressure) is derived from the ideal gas law. moles/liters = molarity Kelvin n P = RTi V 0.082 L.atm/mol.K P=MRTi p=MRTi osmotic pressure =

  34. What’s the osmotic pressure of a 2.0M CaCl2 solution at 25oC? CaCl2a Ca+2 + 2Cl-1 i = 3 p=MRTi = (2.0 M) . (0.082 L.atm/mol.K) . (298K) . 3 = 147 atm

More Related