2 Expectations: g ↔ mol (using molar mass) g ↔ mL (using density) Other conversions: temp., pressure, etc.Solve for any variable in a formula.Distinguish between molecular and ionic compounds.Convert between different concentration units.Describe the properties of solutions.
3 13.1 The Solution Process Solution – homogeneous mixture Solute – present in smaller quantitySolvent – present in larger quantityIntermolecular forces are rearranged when a solute and solvent are mixed.
4 Making a Solution Solute molecules separate (endothermic) Solvent molecules separate (endothermic)Formation of solute-solvent interactions (exothermic)ΔHsoln = total energyΔHsoln – enthalpy change for the formation of a solution; exothermic – usually favorable; endothermic – usually unfavorable
6 Will a solution form?Solute-solvent interaction must be stronger or comparable to the separation of solute and solvent particles.Intermolecular forces play a key role.Entropy (disorder) is also a factor.Disorder is favorable. (2nd law of thermodynamics)Solution formation increases entropy.Dissolve vs. react (p )
7 Entropy in Solution Formation Ionic compoundvery orderedAs the ionic compound dissolves, itbecomes more disordered.
8 13.2 Saturated Solutions and Solubility Saturated solution – solution is in equilibrium with undissolved solute.Solute + solvent ⇌ solutionUnsaturated – less solute than saturatedSupersaturated – more solute than saturateddissolutioncrystallization
9 A Saturated SolutionA dynamic equilibrium – ions continually exchange between the solid and solution form.
10 13.3 Factors Affecting Solubility Like dissolves like, i.e. same polarity.Polar solutes are soluble in polar solvents.Nonpolar solutes are soluble in nonpolar solvents.If two liquids: miscible or immiscibleExamples:✔ water + alcohol, NaCl + water, hexane + pentane✘ water + hexane, NaCl + benzene, oil + water
12 13.3 Factors Affecting Solubility Pressure Effects (for gases in any liquid solvent)Solubility increases as the partial pressure above the solution increases.Henry’s Law: Sg = kPgSg – solubility of gask – Henry’s Law constant; conc./pressure unitsPg – partial pressure of gas above solution
13 The partial pressure of O2 in your lungs varies from 25 to 40 torr The partial pressure of O2 in your lungs varies from 25 to 40 torr. What molarity of O2 can dissolve in water at each pressure? The Henry’s Law constant for O2 is 6.02 x 10-5 M/torr.
14 13.3 Factors Affecting Solubility Temperature EffectsFor solids: Solubility ↑ as temperature ↑ - usually.If ΔHsoln > 0 (endothermic)If ΔHsoln < 0 (exothermic)For gases: Solubility ↓ as temperature ↑ - always.Kinetic energy plays a primary role.Entropy is also a factor.
17 13.4 Ways of Expressing Concentration Mass %, volume %, and ppm
18 13.4 Ways of Expressing Concentration, cont. Mole fraction, molarity, and molality
19 44. A solution contains 80.5 g ascorbic acid (C6H8O6) in 210 g water and has a density of 1.22 g/mL at 55°C. Calculate mass %, X, m, and M.
20 51. Commercial aqueous nitric acid has a density of 1 51. Commercial aqueous nitric acid has a density of 1.42 g/mL and is 16 M. Calculate mass % of HNO3.
21 43. A sulfuric acid solution containing 571 43. A sulfuric acid solution containing g of H2SO4 per liter of solution has a density of g/cm3. Calculate the mass %, mole fraction, molality, and molarity.
22 Concentration Problems Practice!See Figure 13.19, p. 545, for conversion map.Several examples on pp
23 13.5 Colligative Properties The addition of a solute to a pure solvent:Lowers the vapor pressureLowers the freezing pointRaises the boiling pointCauses movement through a semipermeable membrane (osmosis)Depends on the number of solute particles (moles), not the identity; more particles the greater the effectIonic compounds cause an even greater effect.
25 1. Lowering the vapor pressure Addition of solute blocks the solvent from evaporation.More solute, less vapor, lower vapor pressureRaoult’s Law (for a nonvolatile solute):PA = XAPA° PA – solvent v. p. over solution(PA < PA°) PA° – pure solvent v. p.XA – mole fraction of solvent
26 1. Lowering the vapor pressure, cont. When a volatile solute is added, both the solvent and solute contribute to the vapor pressure.“Expanded” Raoult’s Law:Ptotal = PA + PB = XAPA° + XBPB°If a solution obeys Raoult’s Law, it is an ideal solution.Nonideal solutions have strong intermolecular interactions which lower the vapor pressure of the solution even further.
28 62a. Calculate the vapor pressure above a solution of 32 62a. Calculate the vapor pressure above a solution of 32.5 g C3H8O3 (glycerin-nonvolatile) in 125 g water at 343 K. The vapor pressure of water at 343 K is torr.
29 63. A solution is made from equal masses of water and ethanol (C2H5OH) 63. A solution is made from equal masses of water and ethanol (C2H5OH). Calculate the vapor pressure above the solution at 63.5°C. The vapor pressures of water and ethanol are 175 and 400. torr, respectively, at 63.5°C.
30 2. Boiling point elevation 3. Freezing point depression Since a solution has a lower vapor pressure:A higher temperature is needed to boil solutionA lower temperature is needed to freeze solution.To calculate effect:b.p. ↑ ΔTb = Kb·m solution − solventf.p. ↓ ΔTf = Kf·m solvent − solutionΔT – difference between boiling or freezing points of the pure solvent and solutionK – boiling or freezing pt. dep. constant (specific to solvent)m – molality
31 69a. Calculate the freezing and boiling points of a solution that is 0 69a. Calculate the freezing and boiling points of a solution that is 0.40 m glucose in ethanol. For ethanol: f.p °C, b.p. 78.4°C, Kf = 1.99 °C/m, Kb = 1.22 °C/m
32 72. Calculate the molar mass of lauryl alcohol when 5 72. Calculate the molar mass of lauryl alcohol when 5.00 g of lauryl alcohol is dissolved in kg benzene (C6H6). The freezing point of the solution is 4.1°C. For benzene: f.p. 5.5°C, Kf = 5.12 °C/m
33 4. OsmosisOsmosis – movement of solvent molecules through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentrationDriving force – to dilute the higher concentrationContinues until:Equilibrium is reached between two solutions, orExternal pressure prevents further movement.
35 Osmosis in red blood cells Hypertonic solution Hypotonic solution
36 4. Osmosis, cont. Osmotic pressure P = M R T P – osmotic pressure (atm)M – molarityR – L∙atom/mol∙KT – temperature (K)Good technique for measuring molar mass of large molecules like proteins
37 4. Osmosis, cont. Applications: Kidney dialysisIntercellular transportReverse osmosis – apply external pressure to reverse the flow of solvent moleculesWater purification – alternative to salt ion exchangeDesalination – purification of salt water
38 78. A dilute aqueous solution of an organic compound is formed by dissolving 2.35 g in water to form L of solution. The resulting solution has an osmotic pressure of atm at 25°C. Calculate the molar mass of the compound.
39 13.6 Colloids Colloid or colloidal dispersion Intermediate between a solution and a suspensionDispersing medium – analogous to solventDispersing phase – analogous to solute; typically large molecules with high molar massesDoes not settleTyndall effect – particles scatter light
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