Class Note for CHEM 112 at UMass(35)
Class Note for CHEM 112 at UMass(35)
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This 10 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Massachusetts taught by a professor in Fall. Since its upload, it has received 16 views.
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Date Created: 02/06/15
What Chapt 14 will explain to us Why do we put salt on our icy side walks Why do we add salt to the water we will use to cook our pasta Why do we put anti freeze in our car In our windshield washer fluid Some De nitions Films Elwin n Winters A solution is a One constituent is usually HOMOGENEOUS regarded as the mixture of 2 or more SOLVENT and the others substances in a single as SOLUTES phase Concentration Units Molarity M Molality m Concentration Units Molality Molarity M 0100 m K2004 0100 M K2CrO4 1949 K2CrO4 in 100 L total volume 1949 K2Cr04 100 kg H20 Concentration Units Mole Fraction X For a mixture of A B and C WEIGHT Concentration Units ppm Parts per million The EPA s favorite unit Ppm mgmL The MD and the crystallographers s favorite unit Concentration Calculations If we dissolve 621 g 100 mol of ethylene glycol in 250 g of H20 calculate the mol fraction molality weight of ethylene glycol Concentration Calculations Dissolve 621 g 100 mol of ethylene glycol in 250 g of H20 Calculate the mole fraction X of glycol Concentration Calculations Dissolve 621 g 100 mol of ethylene glycol in 250 g of H20 Calculate molality m of glycol Concentration Calculations Dissolve 621 g 100 mol of ethylene glycol in 250 g of H20 Calculate weight ofglycol 10 De nitions Solutions can be classified as saturated or unsaturated A saturated solution contains the maximum quantity of solute that dissolves at that temperature 11 De nitions SUPERSATURATED SOLUTIONS contain more than is possible and are unstable 12 Dissolving a solute miscible vs immiscible Nonpolar I2 Polar H20 Nonpolar CCl4 u was Emokslcaler momsan test tube gt Shake the Polar H20 Nonpolar CZll and 12 Like dissolves like and solubility is based on lMFs 13 Dissolving An Ionic Solid Dipole dipole attraction and hydrogen bonding I39OJ a c z m Cl Ionion attraction de ned by the lattice enthalpy AHmze Iondipnle attraction defined by enthalpy of liydratiun AHmequot 14 Energetics of the Solution Process Kq W9 AH lm39s enthalpy 7 Altmanquot 7aa7 kJmat AH 821 ldmnl EN EREY KF3 715 ldmutf Wall Wall 15 Energetics of the Solution Process red pohlue 5 Mi red pohlue a mmquot mlxed zAH endalhermvc 5mm red 0 nm 0 If the enthalpy of formation of the solution is more negative than that of the solvent and solute the enthalpy of solution is negative and the solution process will be exothermic But predicting the solubility of an ionic solution is tricky because enthalpy is not the only thing that controls a process AGAH TAS 15 Supersaturated Sodium Acetate Sodium acetate has an ENDOTHERMIC heat of solution NaCH3CO2 s heat gt Naaq CH3COZ39aq Therefore formation of solid sodium acetate from its ions is EXOTHERMIC Naaq CH3COZ39aq gt NaCH3CO2 s heat Supersaturated sodium acetate produces heat when the ions come out of solution and form a solid 17 Supersaturated Sodium Acetate One application of a supersaturated solution is the sodium acetate heat packquot Sodium acetate has an ENDOTHERMIC heat of solution it requires heat to dissolve the solid AHsoln 257kJmol 18 Concentration Units An IDEAL SOLUTION is one where the properties depend only on the concentration of solute Need concentration units to tell us the number of solute particles per solvent particle The unit molarity does not do this 19
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