Learning objectives Know the factors that affect solubility Know the different ways to measure concentration and how to convert between them CSB Assignment 1: Unit 15(all) Wed, 3 Sept, 8 AM Announcements Monday office hours: 10 AM ? 12PM Tuesday problem session: 5-6 PM in HHS 1209 Friday?s Clicker Question: My yellow lab is also named after a periodic element. His name can be shortened to the last name of a famous physicist. The relationship E = mc2 is one of this scientist?s numerous accomplishments. What is his name? Bohrium Einsteinium Curium Fermium Mendelevium 1 additional CPS drop for answering correctly! Intermolecular Forces in Solution 1. Ion-dipole forces 2. Hydrogen bonding Intermolecular Forces in Solution 3. Dipole - dipole forces 4. Ion - induced dipole ?Polarizability? Intermolecular Forces in Solution 5. Dipole - induced dipole 6. Dispersion forces (aka London Forces or van der Waals forces) What is the solute-solvent IM? Case 1: CaCO3 dissolves in water Case 2: Table sugar dissolves in water Your choices: 1. Ion-dipole forces 2. Hydrogen bonding 3. Dipole - dipole forces 4. Ion - induced dipole 5. Dipole - induced dipole 6. Dispersion forces (London) Why do substances dissolve? A molecular level picture + solute solvent solution DHrxn = DHsoln Heats of solution: the solution cycle The tradeoff To dissolve salt in water: (a) NaCl must give up ____________ , where DHa ? 786 kJ/mol (b) H2O must give up ____________, where DHb ? 40 kJ/mol (c) In order to gain ________________, where DHc ? 600 kJ/mol DHsoln ? DHa + DHb ? DHc = 226 kJ/mol (actually 3.9 kJ/mol) To dissolve salt in hexane: (a) NaCl must give up ____________ , where DHa ? 786 kJ/mol (b) Hexane must give up ____________, where DHb ? 1 kJ/mol (c) In order to gain ________________, where DHc ? 15 kJ/mol DHsoln ? DHa + DHb ? DHc = 772 kJ/mol (insoluble) To form solutions, solute-solvent interactions must be ____________ in strength to that of the strongest IM in the pure substances! Solubility = like dissolves like interactions broken are of similar strength hexanol in water hexanol Revisiting solubility Which solutes will dissolve in the solvent? NaCl in water E. A & C NaCl in hexane (C6H14) F. A & D Octane (C8H18) in water G. B & C Octane in hexane H. B & D octane hexane Enthalpy of dissolving One more time, but let?s simplify for ionic solutions in water DHsolution = DHsolute + DHsolvent + DHmixing Effect of Temperature Solids: Gases: solids gases similar for all gasses more heat energy ? more E to overcome forces depends on the solid Effect of Pressure: Gases gas + solvent saturated solution Henry?s Law Sgas = kH ? pgas Workshop directions Dr. Warnaar & Workshops in 131 Peer Leaders: Stephanie Hall & David Warnock Today - choose your own group of 4-6 (between 2 rows so you can turn around) Next week In-class activity as part of grade = assigned group and seat Everyone else = form your own group Today: work as a group - not each individually Finish this at home
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