2 Solutions Solutions are stable, homogeneous mixtures Particles are evenly distributed through the mixtureWill not spontaneously separateThere are two parts: solute and solvent
3 Parts of a Solution Solute: the substance being dissolved Solvent: the substance doing the dissolving (think water: universal solvent)
4 Classes of SolutionsClasses are based on the final state of matter of the sol’nThree classes:Gaseous sol’ns: mixtures of two gasesLiquid sol’ns: gas, liquid, or solid is dissolved in a liquidSolid soln’s: solid and a liquid or two solids are melted, mixed, or cooledAlloys: solid solutions containing metals
5 Solution of a gas (hydrogen) in a solid (palladium)
7 Ways to Describe Solutions There are three ways to describe concentrations:MolarityMolalityMole fraction
8 MolarityMolarity (M): # of moles of solute dissolved in each liter of sol’nM = moles of soluteliters of sol’nFour different labels: molarity, molar, M, or mol/LDependent on tempVolumetric flasks are the best containers for making a sol’n of a precise molarity
9 What is the molarity of a sol’n prepared by dissolving 16 What is the molarity of a sol’n prepared by dissolving 16.0 g of barium chloride in enough water to give 450 mL of sol’n?
10 How many grams of potassium chloride are needed to prepare 0 How many grams of potassium chloride are needed to prepare 0.750L of a 1.50M sol’n of potassium chloride?
11 MolalityMolality (m): # of moles dissolved in each kilogram of solventm = moles of solutekg of solventIndependent of temp
12 Calculate the molality of a sol’n prepared by dissolving 20 Calculate the molality of a sol’n prepared by dissolving 20.4 g of sodium chloride in 192g of water.
13 What is the molality of a solid sol’n containing 0 What is the molality of a solid sol’n containing 0.125g of chromium and 81.3g of iron?
14 Mole FractionMole fraction (X): # of moles of one component divided by the total # of moles in the sol’nX = moles of componenttotal moles of sol’nUsed to compare solute and solvent
15 What are the mole fractions of ethyl alcohol (C2H5OH) and water in a sol’n prepared by adding 50.0g of ethyl alcohol to 50.0g of water?
16 A gas mixture contains the following gases with the mole fractions indicated: CH4 (0.510), C2H6 (0.431), C3H8 (0.011), and C4H10 (0.013). The mixture also contains the gas acetylene (C2H2). What is the mole fraction of acetylene?
17 Solution Terms Most sol’ns are combinations of liquids and solids Miscible: liquids or gases that will dissolve in each otherImmiscible: liquids or gases that will not dissolve in each otherSoluble: able to be dissolved in a particular solventInsoluble: not able to be dissolved in a particular solvent
18 ConcentrationsConcentrated solution: a large amount of solute is dissolved in the solventDilute solution: a small amount of solute is dissolved in the solvent
19 SaturationSaturated sol’n: a sol’n that has dissolved all the solute it can hold at a given tempNOT the same as concentratedSol’n can be saturated but not concentrated and vise versa
20 Saturation (cont)Unsaturated sol’n: any sol’n that can dissolve more solute at a given tempSupersaturated sol’n: sol’n that contains more solute than a saturated one has at that tempIt is unstableCrystallization from Supersaturated Solutions of Sodium Acetate
22 Determining Saturation Add a solute crystal to a sol’nIf dissolves: unsaturatedIf does not dissolve: saturatedIf excess solute comes out: supersaturated
23 The Formation of Sol’ns The process of dissolving takes place at the surface of the solid soluteWater molecules orient themselves on the surface of the crystal so that they can separate the pieces and pull them into sol’nOnce separated, the pieces are surrounded by water molecules
25 Formation of Soln (cont) Solvation: process of surrounding solute particles with solvent particlesHydration: solvation involving waterFormation of a sol’n involves:Breaking the attractions among solute particlesBreaking the attractions among solvent particlesFormation of attractions between solute and solvent particles
26 Heat of SolutionDefined as overall energy change that occurs during solution formationEnergy is required for formation of sol’nsBreaking attractions – endothermicForming attractions – exothermicOverall process (net change) depends on the balance between breaking and forming attractionsIf breaking requires more energy – endothermicIf forming releases more energy - exothermic
27 SolubilityDefined as the maximum amount of a solute that will dissolve in a given amount of solvent at a specific tempDetermined experimentallyUsually expressed in grams of solute per 100 grams of solvent at a specific temp and pressure
28 Solubility Based on the idea of attractions between particles Overall polarity determines solubility:“Like dissolves like”Polar dissolves polarNonpolar dissolves nonpolar
31 SolvationThe extent to which one substance dissolves in another depends on:State of solute and solventTemp and pressureSolubilities change with temp (the key to preparing a supersaturated sol’n)Solubility of solids and liquids increasesSolubility of gases in liquids decreases
34 Henry’s LawSolubilities of solids and liquids are not appreciably affected by pressure, but solubility of a gas in a liquid is strongly influenced by pressureHenry’s Law: the amount of gas dissolved in a solvent is proportional to the partial pressure of that gas over the solvent
35 The solubility of a gas depends upon its partial pressure above the solution.
36 Factors that Affect Rate of Solvation Must increase the collisions between solute and solvent particles to increase rate at which solute dissolves.Three ways:Agitate mixture (stir, shake)Increase surface area (breaking solute into small pieces)Increase temp of solvent
37 Increasing surface area does the same thing Because dissolving occurs at the surface, stirring/shaking allows more solvent to come in contact with soluteIncreasing surface area does the same thingAs temp increases, solvent particles move faster, which causes more particles to come in contact with the solute.Particles of solvent have more energy to remove particles from the solid solute
38 Aqueous Solutions Ionic compounds dissociate in water Dissociate: a process using energy to separate a compound into ions in waterMolecular compounds may also dissociate in waterSome aqueous solutions conduct electricity
39 Aqueous Soln’sConductance: the measurement of a sol’n’s ability to conduct electrical energyElectrolyte: any substance that will conduct an electric current (by means of movement of ions), when dissolved in sol’nNonelectrolyte: any substance that will not conduct an electric current when dissolved in water
40 Colligative Properties A physical property that is dependent on the # of particles present rather than on the size, mass, or characteristics of those particlesFour main properties:Vapor pressure reductionBoiling point elevationFreezing point depressionOsmotic pressure
41 Vapor Pressure Reduction Vapor pressure of a solvent containing a nonvolatile solute is lower than the vapor pressure of the pure solventVolatile means tending to evaporate readilyVapor pressure reduction is proportional to concentration
42 When a solute is added to the solvent, some of the solute molecules occupy the space near the surface of the liquid, as shown in the figure to the left. When a solute is dissolved in a solvent, the number of solvent molecules near the surface decreases, and the vapor pressure of the solvent decreases.
43 Boiling Point Elevation Because vapor pressure is lower, a higher temp will be needed to make the sol’n boilThe amount by which the boiling point is raised is the boiling point elevation (ΔTb)It is directly proportional to the sol’n’s molarity
44 A close-up plot of vapor pressure versus temperature for pure water (red curve) and for a 1.0 M NaCl solution (green curve). Pure water boils at 100.0°C, but the solution does not boil until 101.0°C.
45 Freezing Point Depression The presence of solute molecules will lower the freezing point of a substanceThe more solute particles in sol’n, the greater the lowering of the freezing ptFreezing pt depression: the ability of a dissolved solute to lower the freezing point of its sol’nWhy does salt melt ice?
46 Osmotic PressureWhen a semipermeable membrane is placed between 2 sol’ns so that only solvent particles can move through it, a net flow of solvent molecules will occur from the less concentrated sol’n to the more concentrated sol’n (osmosis)Osmotic pressure: the pressure required to prevent osmosisIf 2 different sol’ns have identical osmotic pressure, no osmosis will occur (isotonic)
47 A solution inside the bulb is separated from pure solvent in the container by a semipermeable membrane. Net passage of solvent from the container through the membrane occurs, and the liquid in the tube rises until an equilibrium is reached. At equilibrium, the osmotic pressure exerted by the column of liquid in the tube is sufficient to prevent further net passage of solvent.
48 Heterogeneous Mixtures Suspension: mixture that appears to be uniform while being stirred, but separates into different phases when agitation ceasesColloid: heterogeneous mixture that contains intermediate size particles evenly distributed through a dispersion medium
50 Heterogeneous Mixtures Brownian Motion: jerky, erratic movement of dispersed particlesPrevent colloids from settling outWhat is Brownian Motion?Tyndall effect: scattering of light by dispersed particles
51 The light beam is not visible as it passes through a true solution (right), but it is readily visible as it passes through colloidal silver in water.