Hóa học - Chapter 5: Solutions

Chapter 5Solutions*Solutionhomogeneous mixturescomposition may vary from one sample to anotherappears to be one substance, though really contains multiple materialsmost homogeneous materials we encounter are actually solutionse.g., air and sea waternature has a tendency toward spontaneous mixinggenerally, uniform mixing is more energetically favorable*Solutionssolute is the dissolved substanceseems to “disappear”“takes on the state” of the solventsolvent is the substance solute dissolves indoes not appear to change statewhen both solute and solvent have the same state, the solvent is the component present in the highest percentagesolutions in which the solvent is water are called aqueous solutions*Seawaterdrinking seawater will dehydrate you and give you diarrheathe 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*Common Types of SolutionSolution PhaseSolute PhaseSolvent PhaseExamplegaseous solutionsgasgasair (mostly N2 & O2)liquid solutionsgasliquidsolidliquidliquidliquidsoda (CO2 in H2O)vodka (C2H5OH in H2O)seawater (NaCl in H2O)solid solutionssolidsolidbrass (Zn in Cu)solutions that contain Hg and some other metal are called amalgamssolutions that contain metal solutes and a metal solvent are called alloys*BrassTypeColor% Cu% ZnDensityg/cm3MP°CTensileStrengthpsiUsesGildingredish9558.86106650Kpre-83 pennies,munitions, plaquesCommercialbronze90108.80104361Kdoor knobs,grillworkJewelrybronze87.512.58.78103566Kcostume jewelryRedgolden85158.75102770Kelectrical sockets,fasteners & eyeletsLowdeep yellow80208.6799974Kmusical instruments,clock dialsCartridgeyellow70308.4795476Kcar radiator coresCommonyellow67338.4294070Klamp fixtures,bead chainMuntz metalyellow60408.3990470Knuts & bolts,brazing rods*Solubilitywhen one substance (solute) dissolves in another (solvent) it is said to be solublesalt is soluble in waterbromine is soluble in methylene chloridewhen one substance does not dissolve in another it is said to be insolubleoil is insoluble in waterthe solubility of one substance in another depends on two factors – nature’s tendency towards mixing, and the types of intermolecular attractive forces*Spontaneous Mixing*Solubilitythere is usually a limit to the solubility of one substance in anothergases are always soluble in each othertwo liquids that are mutually soluble are said to be miscible alcohol and water are miscibleoil and water are immisciblethe maximum amount of solute that can be dissolved in a given amount of solvent is called the solubilitythe solubility of one substance in another varies with temperature and pressure*Mixing and the Solution ProcessEntropyformation of a solution does not necessarily lower the potential energy of the systemthe difference in attractive forces between atoms of two separate ideal gases vs. two mixed ideal gases is negligibleyet the gases mix spontaneouslythe gases mix because the energy of the system is lowered through the release of entropyentropy is the measure of energy dispersal throughout the systemenergy has a spontaneous drive to spread out over as large a volume as it is allowed*Intermolecular Forces and the Solution ProcessEnthalpy of Solutionenergy changes in the formation of most solutions also involve differences in attractive forces between particlesmust overcome solute-solute attractive forces endothermicmust overcome some of the solvent-solvent attractive forcesendothermicat least some of the energy to do this comes from making new solute-solvent attractionsexothermic*Intermolecular Attractions*Relative Interactions and Solution Formationwhen 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 entropySolute-to-Solvent>Solute-to-Solute +Solvent-to-SolventSolution FormsSolute-to-Solvent=Solute-to-Solute +Solvent-to-SolventSolution FormsSolute-to-Solvent<Solute-to-Solute +Solvent-to-SolventSolution May or May Not Form