C121 11-3 lec35GL

C121 11-3 lec35GL - Lecture 35 December 2, 2011 Properties...

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Lecture 35 December 2, 2011 Properties of Solutions Last Day: Properties of Solutions (Chapter 17) Solubility and Intermolecular Forces Solubility and Pressure Vapour Pressure of Solutions Today: Properties of Solutions (Chapter 17) Ideal and Non-Ideal Solutions Colligative Properties Boiling Point Elevation Freezing Point Depression Osmotic Pressure van’t Hoff Factor
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Type of Examples Soluble In Factors Affecting Solute Solubility Ionic NaCl, KNO 3 Polar Solvents Solvent dipoles +/- ions CaSO 4 , etc. Ex. H 2 O δ+/ δ- interact (H-Bonding) with ions +/- small alcohols most soluble: CH 3 OH, large anions with CH 3 CH 2 OH small charges (Table 4.1 Solubility) Covalent (i) I 2 , CCl 4 Non-polar London Dispersion Forces (Σμ = 0) C 6 H 6 Solvents dominate solute-solvent non-polar (ii) long chain ex. CCl 4 , CS 2 interactions hydrocarbons hexanes C 6 H 14 (exception: if there are CH 3 (CH 2 ) n CH 3 CHCl 3 , CH 2 Cl 2 multiple polar groups small dipoles i.e. -NH 2 , -CO 2 H, -OH hydrocarbons solubility in polar solvents increases Polar CH 3 CO 2 H, HI Polar Solvents Dipole-Dipole Forces Covlaent NH 3 (as above) dominate the solute-solvent (Σμ ≠ 0) interactions (δ+/ δ-)
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Solubility and Pressure solutes but does affect solubility of gases solubility of gas pressure of gas in solution above solvent Henry’s Law P A = k A χ A or P A = k A C A ~
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Solubility and Temperature solubility of gas in solution temperature dependence of solubility of solids is more complex: some increase (most ionic solids) some decrease (Na 2 SO 4 , CeSO 4 ) some stay constant (NaCl) increasing temperature does increase rate of dissolution ~ 1 T
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The presence of a nonvolatile solute inhibits the escape of solvent molecules from the liquid P 0 solvent P solution >
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presence of non-volatile solute “blocks” some sites at the liquid’s surface fewer solvent molecules get to the vapour phase vapour pressure is reduced. vapour pressure mole fraction of of solution solvent in solution (in general a linear relationship) ~ P solution = χ solvent P 0 solvent Raoult’s Law vapour pressure above solution mole fraction of solvent in solution vapour pressure of pure solvent
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Case 2: Adding a Volatile Solute (has its own vapour pressure) solution containing both a volatile solute and a solvent
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This note was uploaded on 12/10/2011 for the course CHEM 121 taught by Professor Leech during the Fall '11 term at Simon Fraser.

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C121 11-3 lec35GL - Lecture 35 December 2, 2011 Properties...

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