Announcements To join clicker to class today: – Turn on the Clicker (the red LED comes on). – Push “Join” button followed by “20” followed by the “Send” button (switches to flashing green LED if successful). ● Starting Chapter 10 next. ● Suggested reading and problems e- mailed to you and on class web site. ● Last exam (chp 9 & 10) one week from Friday. ● Review material is posted. ● Wear appropriate clothes to Lab!

Review H-bonding –Generally weaker than ion-ion interactions –Stronger than other intermolecular interactions. –Only seen for hydrogens bonded to N, O or F. –Bond to lone pair on another molecule (usually on N, O or F). –Explain very high boiling points for H 2 O, NH 3 and HF Solubility –“like dissolves like” (polar in polar, nonpolar in nonpolar) –Only soluble if dissolved particles lower energy than undissolved solid.

Raoult’s Law of Vapor Pressure Raoult’s Law: P vap = X solvent P˚ solvent –P vap = vapor pressure of solvent above the solution –X solvent = mole fraction of solvent particles in the solution note n tot = n solv + in solute (may include + & - ions) X solvent =n solv /(n solv + in solute ) –P˚ solvent = vapor pressure of pure solvent at the temperature of interest. Implication: increasing non-volatile solute concentration lowers the vapor pressure of the solvent.

Blocking of evaporation by solute Fig 9.10

CO 2 H 2 O Fig Fig. 9.12

Water on a hydrophobic (nonpolar) surface Picture courtesy of: The University of British Columbia Structured Surface Physics Laboratory

Surface Tension and Meniscus Fig 9.15 Fig 9.16