Properties of Solutions - Lecture Slides | CHEM 162, Study notes of Chemistry

Download Properties of Solutions - Lecture Slides | CHEM 162 and more Study notes Chemistry in PDF only on Docsity! 1 Chapter 17 - Properties of Solutions 17.1 Solution Composition 17.2 Thermodynamics of Solution Formation 17.3 Factors Affecting Solubility 17.4 Vapor Pressures of Solutions 17.5 Boiling-Point Elevation and Freezing-Point Depression 17.6 Osmotic Pressure 17.7 Colligative Properties of Electrolyte Solutions 17.8 Colloids Definitions for Solutions Solute - The smaller (in mass) of the components in a solution, the material dispersed into a solvent. Solvent - The major component of the solution, the material that the solute is dissolved into. Solubility - The maximum amount that can be dissolved into a particular solvent to form a stable solution at a specified temperature. Miscibility - The ability of two substances to dissolve in one another in any proportion. 2 Gas-Gas Solutions Gas-Liquid Solutions Solid-Solid Solutions etc. (see Table 17.1) The formation of solutions from pure substances is always favored by ENTROPY! When two pure substances are mixed, the disorder of the system is increased As with any chemical reaction, solvation is a balance between enthalpy and entropy Gibbs Free Energy ∆G° = ∆H° - T∆S ° Like dissolves Like: solubility of methanol in water A.solution of water and methanol Solubility of Alcohols in Water and Hexane Alcohol Model Water Hexane CH,OH G (methanol) 3 ° oe CH,CH,OH o o (ethanol) CH,(CH,) OH . co (propanol) CH,(CH,),0H fee (butanol) 0.11 ° CH,(CH,),OH (pentanol) 0.030 ° CH,(CH,),OH r (hexanol) 0.0058 ° * Expressed in mol alcohol/100 g solvent at 20°C.  lon-dipole Hydration forces _ Se shells ak # y Hydration shells around an aqueous ion Hydrogen™<— bonds _—_ Mafarated” Enthalpy z 27 ant ago = Diagrams Bi Hexane] 22 core . . £ |separated ze 2 for Dissolving = az “ls z NaCl and jf [Hexane NaCl(s) Octane in <i aggregated | jaggregated Toa Hexane A = Hexane Octane S |separated| separated] AH.oiute S| ~ AHsoivent z i Hexane : Octane] AMimix "EE lagoregatea|3 lacorcanted Hina Solution] DHsoin =O B Hina 7 Predicting Relative Solubilities of Substances Problem: Predict which solvent will dissolve more of the given solute. (a) Sodium Chloride in methanol (CH3OH) or in propanol (CH3CH2CH2OH). (b) Ethylene glycol (HOCH2CH2OH) in water or in hexane (CH3CH2CH2CH2CH2CH3). (c) Diethyl ether (CH3CH2OCH2CH3) in ethanol (CH3CH2OH) or in water. Plan: Examine each solute and solvent to determine which intermolecular forces will be active. A solute tends to be more soluble in a solvent that has the same type of intermolecular forces active. Predicting Relative Solubilities of Substances - II Solution: (a) Methanol - NaCl is an ionic compound that dissolves through ion- dipole forces. Both methanol and propanol contain a polar O-H group, but propanol’s longer hydrocarbon chain would interact only weakly with the ions and be less effective in stabilizing the ions. (b) Water - Ethylene glycol has two O-H groups and is stabilized by extensive H-bonding in water. (c) Ethanol - Diethyl ether shows both dipolar and dispersion intermolecular forces and could form H bonds to both water and ethanol. The ether would be more soluble in ethanol because solvation in water must disrupt many more strong H-bonding interactions.