Chapter 10 Student Notes PHW

Chapter 10 Student Notes PHW - Chapter 10 Objectives 10.1...

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Unformatted text preview: Chapter 10 Objectives 10.1 Define solutions and the different mathematical methods for describing solution composition. 10.2 Provide a qualitative and pictorial description of vapor pressure. pressure. 10.3 Discuss Raoult’s Law in a quantitative and qualitative method Raoult’ for describing vapor pressure. 10.4 Outline the role of colligative properties and provide mathematical and qualitative descriptions for colligative properties. On Exam 2, students will be responsible for all sections of Chapter 10 except section 10.2, pp. 461−467. 461− 10/6/2009 Zumdahl Chapter 17 Solution Composition 10.1 1 The solute and solvent can be any combination of solid (s), liquid (l), and (s (l gaseous (g) phases. (g Dissolution: Two (or more) substances spread out, or disperse, into each other at the level of individual atoms, molecules, or ions. Solution: Solvent: Solute(s): Solute(s): 10/6/2009 Zumdahl Chapter 17 2 1 Measures of Solution Composition Mass Fraction, Mole Fraction, Molality, Molarity Mass percentage (weight percentage): mass percentage of a component = mass of component total mass of mixture Mole fraction: × 100% The chemical amount (in moles) divided by the total amount (in moles) X1 = n1 / (n1 + n2 + n3 + …) X1 + X2 + X3 + … = 1 and n1 + n2 + n3 +… = n 10/6/2009 Zumdahl Chapter 17 3 Molality msolute = Units: moles per kg or mol kg-1 Molarity csolute = Units: moles per liter or mol L-1 10/6/2009 Zumdahl Chapter 17 4 2 Factors Affecting Solubility 1. Structure Effects – Review chapter 4 – “Like Dissolves Like” concept Like” – Polar molecules, water soluble, hydrophilic (water loving) molecules, • E.g., Vitamins B and C; water-soluble – Non-polar molecules, soluble in non-polar molecules, Nonmolecules, nonhydrophobic (water fearing) • E.g., Vitamins A, D, K and E; fat-soluble Vitamin A 10/6/2009 Vitamin C Zumdahl Chapter 17 5 Factors Affecting Solubility (con’t) 1. Structure Effects 2. Pressure Effects Henry’s Law (for dilute solutions) Henry’ The vapor pressure of a volatile solute in a sufficiently dilute solution is proportional to the mole fraction of the solute in the solution. solution. kH is the kH depends on temperature and on strength of solute-solvent interaction solute- 10/6/2009 Zumdahl Chapter 17 6 3 When the partial pressure of nitrogen over a sample of water at 19.4°C is 9.20 atm, then the concentration of nitrogen in the water is 5.76 x 10-3 mol L-1. Compute the Henry’s law constant for nitrogen Henry’ in water at this temperature. temperature. Given PN cN = 9.20 atm 2 = [N 2 ] = 5.76x10 2 Henry' s Law PN = k N X N 2 2 = XN 2 nN ≈ 2 nN + nH 10/6/2009 2 O = [N 2 ] = 5.76x10 −3 X = kN X 2 N 2 = 2 N nN nN 2 2 O = 2 ≈ 2 + nH 7 mol/l Henry' s Law PN nH 2 XN2 ≈ nN2 / nH2O = 9.20 atm 2 2 nN Zumdahl Chapter 17 Given cN mol/l 2 2 PN −3 2 O nN nH −3 5.76 x 10 mol/L _________________________ (1000 g/L) / (18.0 g/mol) 2 2 O Therefore, = 9.20 atm / 1.04 x 10−4 kN2 = 8.86 x 10−4 atm 10/6/2009 Zumdahl Chapter 17 8 4 Factors Affecting Solubility (con’t) 1. 2. 3. Structure Effects Pressure Effects Temperature Effects for Aqueous Solutions (a) The aqueous solubilities of a majority of solids increase with increasing temperature, but some decrease with temperature, increasing temperature 10/6/2009 Zumdahl Chapter 17 9 Factors Affecting Solubility (con’t) 1. 2. 3. Structure Effects Pressure Effects Temperature Effects for Aqueous Solutions (b) The aqueous solubilities of most gases decrease with increasing temperature. temperature. In solvents other than water, gas solubilities often increase with increasing temperature. 10/6/2009 Zumdahl Chapter 17 10 5 The Person Behind the Science Francois-Marie Raoult (1830-1901) Highlights – 1886 Raoult's law , the partial pressure of a solvent vapor in equilibrium with a solution is proportional to the ratio of the number of solvent molecules to nonnonvolatile solute molecules. – allows molecular weights to be determined, and provides the explanation for freezing point depression and boiling point elevation. elevation. For ideal solutions Moments in a Life – Raoult was a prominent member of the group which created physical chemistry, including Arrhenius, Nernst, van‘t Hoff, van‘ Planck. 10/6/2009 Zumdahl Chapter 17 11 Raoult’s Law • Consider a non-volatile solute (component 2) in a solvent non(component 1) that has a measurable vapor pressure • X1 = mole fraction of solvent Raoult’s Law Raoult’ Solvent always obeys Raoult’s Raoult’ Law in the limit where X1 → 1 Positive (Negative) Deviation from Ideality Solute(s) always obey Henry’s Solute(s) Henry’ Law in the limit of Zumdahl Chapter 17 infinite dilution 12 solute−solvent attractions < (>) solute− solvent−solvent attractions solvent− 10/6/2009 6 Ideal Solution P1 = X1 P°1 P2 = X2 P°2 10/6/2009 Zumdahl Chapter 17 13 Vapor Pressure of a Solution of Two Volatile Liquids 10.4 10/6/2009 Zumdahl Chapter 17 14 7 Colligative Properties of Solutions • For some physical properties, the difference between a pure solvent and a dilute solution depends only on the number of solute particles present and not on their chemical identify. Such properties are called Colligative Properties. Properties. • Colligative Properties include – V – B – F – O 10/6/2009 Zumdahl Chapter 17 15 The vapor pressure of a solvent above a dilute solution is always always less than the vapor pressure above the pure solvent. The boiling point of a solution of a non-volatile solute in a volatile nonsolvent always exceeds the boiling point of a pure solvent Boiling: Liquid in equilibrium with vapor Boiling Point: Temp. at which Psolvent = Pext ion De po sit Su b lim a ti on GAS SOLID n tio sa en on nd at i Co or ap Ev Normal boiling point: Psolvent = 1 atm Melting LIQUID Freezing 10/6/2009 Zumdahl Chapter 17 16 8 Elevation of Boiling Point and Lowering of Vapor Pressure ∆T = K m b solute ∆T is the boiling point elevation Kb is molal boiling - point elevation constant m is the molality of the solute in solution solute Phase diagrams for pure water (red lines) (red lines) and for an aqueous solution containing a nonvolatile solution (blue lines) (blue lines) 10/6/2009 Zumdahl Chapter 17 17 Zumdahl Chapter 17 18 10.5 10/6/2009 9 Osmotic Pressure Important for transport of molecules across cell membranes, called semipermeable membranes Osmotic Pressure = Π = g d h PV = nRT c = Molarity or moles/L = n / V 10/6/2009 Zumdahl Chapter 17 19 Osmotic Pressure (con’t) The normal flow of solvent into the solution (osmosis) can be prevented by applying an external pressure to the solution. Osmotic Pressure useful for Determining the Molar Mass of protein and other macromolecules Small concentrations cause large osmotic pressures Can prevent transfer of all solute particles Dialysis at the wall of most plant and animal cells 10/6/2009 Zumdahl Chapter 17 20 10 Dialysis A cellophane (polymeric) tube acts as the semisemipermeable membrane Purifies blood by washing impurities (solutes) into the dialyzing solution. Representation of the functioning of an artificial kidney 10/6/2009 Zumdahl Chapter 17 21 Sample Problem A dilute aqueous solution of a non-dissociating compound contains non1.19 g of the compound per liter of solution and has an osmotic pressure of 0.0288 atm at a temperature of 37°C. Compute the 37° molar mass of the compound. Strategy 1.) use Π = cRT to find the c in mol/L g Molar mass g Given g l = = 3 .) Rearrange M = c mole mole l 2.) Recall that mole = 10/6/2009 Zumdahl Chapter 17 22 11 A dilute aqueous solution of a non-dissociating compound contains 1.19 g of the noncompound per liter of solution and has an osmotic pressure of 0.0288 atm at a 0.0288 temperature of 37°C. Compute the molar mass of the compound 37° Solution c = = 0.0288 atm / (0.0821 L atm mol−1 K−1) (310. K) c = 1.13 x 10−3 mol L−1 M = M = 1050 g mol−1 10/6/2009 Zumdahl Chapter 17 23 The Person Behind the Science J.H. van’t Hoff (1852-1901) Highlights – Discovery of the laws of chemical dynamics and osmotic pressure in solutions – Mathematical laws that closely resemble the laws describing the behavior of gases. gases. – his work led to Arrhenius's theory of electrolytic dissociation or ionization – Studies in molecular structure laid the foundation of stereochemistry. stereochemistry. van’t Hoff Factor (i) van’ (i Moments in a Life – 1901 awarded first Noble Prize in Chemistry 10/6/2009 Zumdahl Chapter 17 ∆T = − i m K 24 12 Colligative Properties of Electrolyte Solutions Elevation of Boiling Point ∆Tb = m Kb 10.6 (m = molality) molality) The Effect of Dissociation (i = the number of particles released into the solution per formula unit of solute) e.g., NaCl dissociates into i = 2 (Na+ + Cl−) e.g., Na2SO4 dissociates into i = 3 (2 Na+ + 1 SO42−) e.g., acetic acid (a weak acid and weak electrolyte) dissociates only slightly so i ≈ 1 10/6/2009 Analogously, for Depression of Freezing Pt. Zumdahl Chapter 17 25 Colloids: Colloidal Dispersions – 1nm to 1000 nm in size • Examples – – – – – – – Opal (water in solid SiO2) Aerosols (liquids in Gas) Smoke (solids in Air) Milk (fat droplets & solids in water) Mayonnaise (water droplets in oil) Paint (solid pigments in liquid) Biological fluids (proteins & fats in water) • Characteristics – Larger particle sizes: translucent, cloudy, milky – Smaller particle sizes: can be clear – Ionic Layers => Resistance to coagulation (see text, pp. 487-489) (see 487- 489) 10/6/2009 Zumdahl Chapter 17 26 13 Light Scattering by Colloids: The Tyndall Effect 10/6/2009 Zumdahl Chapter 17 27 Zumdahl Chapter 17 28 10.7 10/6/2009 14 Chapter 10 Properties of Solutions 10.1 Solution Composition 10.2 The Thermodynamics of Solution Formation (skip) 10.3 Factors Affecting Solubility 10.4 The Vapor Pressures of Solutions 10.5 Boiling-Point Elevation and Freezing-Point Depression BoilingFreezing10.6 Osmotic Pressure 10.7 Colligative Properties of Electrolyte Solutions 10.8 Colloids 10/6/2009 Zumdahl Chapter 17 29 15 ...
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