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chapter 12 notes

# chapter 12 notes - Chapter 12 Physical Properties of...

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©2010 Donald L. Siegel, All Rights Reserved Chapter 12 Chapter 12 Physical Properties of Solutions

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©2010 Donald L. Siegel, All Rights Reserved Solution Composition Solution Composition W In 161, we measured concentration in several ways % composition ppm χ M W We’re introducing a new measure: molality (m) m = moles of solute per kilogram of solvent

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©2010 Donald L. Siegel, All Rights Reserved Example Example W Find the molality of a 1.00% w/w solution of CH 3 CH 2 OH. 1.00g CH 3 CH 2 OH × 1mol/46.07g = 2.17×10 -2 mol 2.17×10 -2 mol/0.10000kg = 0.217m
©2010 Donald L. Siegel, All Rights Reserved Relationship between M and m Relationship between M and m W For dilute solutions, M m W Relationship depends on d W For example, 3.75M H 2 SO 4 has a density of 1.230g/mL. What is its molality? 1L weighs 1230g 1L has 3.75 mol H 2 SO 4 = 368g 1230 – 368 = 862 g H 2 O m = 3.75 mol/0.862kg = 4.35m

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©2010 Donald L. Siegel, All Rights Reserved Enthalpy of solution Enthalpy of solution W The energetics of solution are complicated Enthalpy to overcome intermolecular forces in solute Magnitude depends on compound Magnitude depends on compound Large for polar, ionic compounds Large for polar, ionic compounds Enthalpy to overcome intermolecular forces in solvent Enthalpy of solvation (hydration when water is solvent) W Net result: like dissolves like Polar substances dissolve in polar solvents Nonpolar substances dissolve in nonpolar solvents

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©2010 Donald L. Siegel, All Rights Reserved Non Non - - ideal behavior ideal behavior 50 mL water 50 mL ethanol
©2010 Donald L. Siegel, All Rights Reserved Factors affecting solubility Factors affecting solubility W Structure controls polarity, and therefore solubility Fat soluble (hydrophobic) vs. water soluble (hydrophilic) vitamines W Pressure: Henry’s Law M = k H P k H varies with gas and temperature For most gases, k H decreases at higher temperature W Temperature Most salts are more soluble at higher temp., but depends on sign of H solution

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