Chapter 12 Solutions 2008, Prentice Hall Chemistry: A Molecular Approach, 1 st Ed. Nivaldo Tro Roy...

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Transcript of Chapter 12 Solutions 2008, Prentice Hall Chemistry: A Molecular Approach, 1 st Ed. Nivaldo Tro Roy...

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Chapter 12 Solutions 2008, Prentice Hall Chemistry: A Molecular Approach, 1 st Ed. Nivaldo Tro Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Slide 2 Tro, Chemistry: A Molecular Approach2 Solution homogeneous mixtures composition may vary from one sample to another appears to be one substance, though really contains multiple materials most homogeneous materials we encounter are actually solutions e.g., air and sea water nature has a tendency toward spontaneous mixing generally, uniform mixing is more energetically favorable Slide 3 Tro, Chemistry: A Molecular Approach3 Solutions solute is the dissolved substance seems to disappear takes on the state of the solvent solvent is the substance solute dissolves in does not appear to change state when both solute and solvent have the same state, the solvent is the component present in the highest percentage solutions in which the solvent is water are called aqueous solutions Slide 4 Tro, Chemistry: A Molecular Approach4 Seawater drinking seawater will dehydrate you and give you diarrhea the cell wall acts as a barrier to solute moving the only way for the seawater and the cell solution to have uniform mixing is for water to flow out of the cells of your intestine and into your digestive tract Slide 5 Tro, Chemistry: A Molecular Approach5 Common Types of Solution Solution Phase Solute Phase Solvent PhaseExample gaseous solutionsgas air (mostly N 2 & O 2 ) liquid solutions gas liquid solid liquid soda (CO 2 in H 2 O) vodka (C 2 H 5 OH in H 2 O) seawater (NaCl in H 2 O) solid solutionssolid brass (Zn in Cu) solutions that contain Hg and some other metal are called amalgams solutions that contain metal solutes and a metal solvent are called alloys Slide 6 6 Brass TypeColor% Cu% ZnDensity g/cm 3 MP C Tensile Strength psi Uses Gildingredish9558.86106650Kpre-83 pennies, munitions, plaques Commercialbronze90108.80104361Kdoor knobs, grillwork Jewelrybronze87.512.58.78103566Kcostume jewelry Redgolden85158.75102770Kelectrical sockets, fasteners & eyelets Lowdeep yellow 80208.6799974Kmusical instruments, clock dials Cartridgeyellow70308.4795476Kcar radiator cores Commonyellow67338.4294070Klamp fixtures, bead chain Muntz metalyellow60408.3990470Knuts & bolts, brazing rods Slide 7 Tro, Chemistry: A Molecular Approach7 Solubility when one substance (solute) dissolves in another (solvent) it is said to be soluble salt is soluble in water bromine is soluble in methylene chloride when one substance does not dissolve in another it is said to be insoluble oil is insoluble in water the solubility of one substance in another depends on two factors natures tendency towards mixing, and the types of intermolecular attractive forces Slide 8 Tro, Chemistry: A Molecular Approach8 Spontaneous Mixing Slide 9 Tro, Chemistry: A Molecular Approach9 Solubility there is usually a limit to the solubility of one substance in another gases are always soluble in each other two liquids that are mutually soluble are said to be miscible alcohol and water are miscible oil and water are immiscible the maximum amount of solute that can be dissolved in a given amount of solvent is called the solubility the solubility of one substance in another varies with temperature and pressure Slide 10 Tro, Chemistry: A Molecular Approach10 Mixing and the Solution Process Entropy formation of a solution does not necessarily lower the potential energy of the system the difference in attractive forces between atoms of two separate ideal gases vs. two mixed ideal gases is negligible yet the gases mix spontaneously the gases mix because the energy of the system is lowered through the release of entropy entropy is the measure of energy dispersal throughout the system energy has a spontaneous drive to spread out over as large a volume as it is allowed Slide 11 Tro, Chemistry: A Molecular Approach11 Intermolecular Forces and the Solution Process Enthalpy of Solution energy changes in the formation of most solutions also involve differences in attractive forces between particles must overcome solute-solute attractive forces endothermic must overcome some of the solvent-solvent attractive forces endothermic at least some of the energy to do this comes from making new solute-solvent attractions exothermic Slide 12 Tro, Chemistry: A Molecular Approach12 Intermolecular Attractions Slide 13 Tro, Chemistry: A Molecular Approach13 Relative Interactions and Solution Formation when the solute-to-solvent attractions are weaker than the sum of the solute-to-solute and solvent-to-solvent attractions, the solution will only form if the energy difference is small enough to be overcome by the entropy Solute-to-Solvent> Solute-to-Solute + Solvent-to-Solvent Solution Forms Solute-to-Solvent= Solute-to-Solute + Solvent-to-Solvent Solution Forms Solute-to-Solvent< Solute-to-Solute + Solvent-to-Solvent Solution May or May Not Form Slide 14 Tro, Chemistry: A Molecular Approach14 Solution Interactions Slide 15 Tro, Chemistry: A Molecular Approach15 Will It Dissolve? Chemists Rule of Thumb Like Dissolves Like a chemical will dissolve in a solvent if it has a similar structure to the solvent when the solvent and solute structures are similar, the solvent molecules will attract the solute particles at least as well as the solute particles to each other Slide 16 Tro, Chemistry: A Molecular Approach16 Classifying Solvents SolventClass Structural Feature Water, H 2 OpolarO-H Methyl Alcohol, CH 3 OHpolarO-H Ethyl Alcohol, C 2 H 5 OHpolarO-H Acetone, C 3 H 6 OpolarC=O Toluene, C 7 H 8 nonpolarC-C & C-H Hexane, C 6 H 14 nonpolarC-C & C-H Diethyl Ether, C 4 H 10 OnonpolarC-C, C-H & C-O, (nonpolar > polar) Carbon TetrachloridenonpolarC-Cl, but symmetrical Slide 17 Tro, Chemistry: A Molecular Approach17 Example 12.1a predict whether the following vitamin is soluble in fat or water Vitamin C The 4 OH groups make the molecule highly polar and it will also H-bond to water. Vitamin C is water soluble Slide 18 Tro, Chemistry: A Molecular Approach18 Example 12.1b predict whether the following vitamin is soluble in fat or water Vitamin K 3 The 2 C=O groups are polar, but their geometric symmetry suggests their pulls will cancel and the molecule will be nonpolar. Vitamin K 3 is fat soluble Slide 19 Tro, Chemistry: A Molecular Approach19 Energetics of Solution Formation overcome attractions between the solute particles endothermic overcome some attractions between solvent molecules endothermic for new attractions between solute particles and solvent molecules exothermic the overall H depends on the relative sizes of the H for these 3 processes H soln = H solute + H solvent + H mix Slide 20 Tro, Chemistry: A Molecular Approach20 Solution Process 1. add energy in to overcome solute-solute attractions 2. add energy in to overcome some solvent-solvent attractions 3. form new solute-solvent attractions, releasing energy Slide 21 Tro, Chemistry: A Molecular Approach21 Energetics of Solution Formation if the total energy cost for breaking attractions between particles in the pure solute and pure solvent is less than the energy released in making the new attractions between the solute and solvent, the overall process will be exothermic if the total energy cost for breaking attractions between particles in the pure solute and pure solvent is greater than the energy released in making the new attractions between the solute and solvent, the overall process will be endothermic Slide 22 Tro, Chemistry: A Molecular Approach22 Heats of Hydration for aqueous ionic solutions, the energy added to overcome the attractions between water molecules and the energy released in forming attractions between the water molecules and ions is combined into a term called the heat of hydration attractive forces in water = H-bonds attractive forces between ion and water = ion-dipole H hydration = heat released when 1 mole of gaseous ions dissolves in water Slide 23 Tro, Chemistry: A Molecular Approach23 Heat of Hydration Slide 24 Tro, Chemistry: A Molecular Approach24 Ion-Dipole Interactions when ions dissolve in water they become hydrated each ion is surrounded by water molecules Slide 25 Tro, Chemistry: A Molecular Approach25 Solution Equilibrium the dissolution of a solute in a solvent is an equilibrium process initially, when there is no dissolved solute, the only process possible is dissolution shortly, solute particles can start to recombine to reform solute molecules but the rate of dissolution >> rate of deposition and the solute continues to dissolve eventually, the rate of dissolution = the rate of deposition the solution is saturated with solute and no more solute will dissolve Slide 26 Tro, Chemistry: A Molecular Approach26 Solution Equilibrium Slide 27 Tro, Chemistry: A Molecular Approach27 Solubility Limit a solution that has the maximum amount of solute dissolved in it is said to be saturated depends on the amount of solvent depends on the temperature and pressure of gases a solution that has less solute than saturation is said to be unsaturated a solution that has more solute than saturation is said to be supersaturated Slide 28 Tro, Chemistry: A Molecular Approach28 How Can You Make a Solvent Hold More Solute Than It Is Able To? solutions can be made saturated at non-room conditions then allowed to come to room conditions slowly for some solutes, instead of coming out of solution when the conditions change, they get stuck in-between the solvent molecules and the solution becomes supersaturated supersaturated solutions are unstable and lose all the solute above saturation when disturbed e.g., shaking a carbonated beverage Slide 29 Tro, Chemistry: A Molecular Approach29 Adding Solute to a Supersaturated Solution of NaC 2 H 3 O 2 Slide 30 Tro, Chemistry: A Molecular Approach30 Temperature Dependence of Solubility of Solids in Water solubility is generally given in gram