Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION Chapter 11 Properties of Solutions

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Section 11.5 Colligative Properties Depend only on the number, not on the identity, of the solute particles in an ideal solution. 4 Boiling point elevation 4 Freezing point depression 4 Osmotic pressure

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 BOILING POINT ELEVATION A Non-Volatile Solute -- ELEVATES THE BOILING POINT OF THE SOLVENT -- LOWERS THE VAPOR PRESSURE OF THE SOLVENT SOL’N MUST BE HEATED TO A HIGHER TEMPERATURE THAN THE Boiling Point OF THE PURE SOLVENT TO REACH A VAPOR PRESS. OF 1 atm.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Red lines are pure water; Blue lines are aqueous sol’n containing nonvolatile solute.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Boiling Point Elevation A nonvolatile solute elevates the boiling point of the solvent.  T = K b m solute K b = molal boiling point elevation constant m = molality of the solute

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Freezing Point Depression A nonvolatile solute depresses the freezing point of the solvent.  T = K f m solute K f = molal freezing point depression constant m = molality of the solute

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Adding solute  Extends Liquid range

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Homework Have you done yours???

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Section 11.6 Osmotic Pressure Osmosis: The flow of solvent into the solution through the semipermeable membrane. Semipermeable Membrane: membrane that allows solvent to pass through but not solute.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure Osmotic Pressure Net transfer of solvent molecules into the Solution until the hydrostatic pressure equalizes the solvent flow in both directions.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Because the liquid level for the solution is higher, there is greater hydrostatic pressure on the solution than on the pure solvent, Osmotic Pressure: The excess hydrostatic pressure on the solution compared to the pure solvent.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure Osmosis Osmotic Pressure: Minimum Pressure required to stop flow of solvent into the solution.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Figure Osmosis at Equilibrium

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 OSMOTIC PRESSURE   = M R T where M = Molarity R = Gas Law Constant T = Temperature in Kelvin

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Colligative Properties useful for -- characterizing the nature of a solute after it is dissolved in a solvent and -- determining molar masses of substances. Osmotic Pressure measurements generally give much more accurate Molar Mass values than those from Freezing-point or Boiling-point changes.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 DIALYSIS SIMILAR TO OSMOSIS Membrane, however, allows transfer of both solvent molecules & small solute molecules & ions. ONE MOST IMPORTANT APPLICATION: Artificial Kidney Machines to purify the blood.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Figure A Representation of the Functioning of an Artificial Kidney

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 ISOTONIC SOLUTIONS: Solutions that have Identical Osmotic Pressure

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 HYPERTONIC SOLUTIONS: Solution having an Osmotic Pressure higher Than that of the cell fluids. Cells shrivel because net transfer of water is Out of the cells  CRENATION HYPOTONIC SOLUTION: Solution having an Osmotic Pressure lower than that of the cell fluids. Cells swell because of net flow of water into the cells  Cell Rupture  HEMOLYSIS

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Homework !!!!!!

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 If the external pressure is larger than the osmotic pressure, reverse osmosis occurs. One application is desalination of seawater. REVERSE OSMOSIS

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Figure Reverse Osmosis Net flow of solvent from the solution to the solvent.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Section 11.7 COLLIGATIVE PROPERTIES OF ELECTROLYTE SOLUTIONS DEPENDS ON THE TOTAL CONCENTRATION OF SOLUTE PARTICLES

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Colligative Properties of Electrolyte Solutions  T = imK  = iMRT van’t Hoff factor, “i”, relates to the number of ions per formula unit. NaCl = 2, K 2 SO 4 = 3

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 VALUE of van’t Hoff factor OBSERVED IS NOT ALWAYS VALUE EXPECTED. SEE TABLE 11.6.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Best Explanation is Ion Pairing. At any given instant, a small percentage of the + and – ions, are paired. Therefore, they count as a single particle. These ions are not moving around independently.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Figure Ion Pairs Form in an Aqueous Solution

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 Deviation of van’t Hoff factor i: 1)Observed value very close to expected value in very dilute solutions. 2)Deviation greatest for ions with multiple charge. Homework: