Transcript Solutions
Chapter Eleven: PROPERTIES OF SOLUTIONS Various Types of Solutions Brass Carbonated water (soda) Seawater, sugar solution State of Solution Gas Liquid Solid Liquid Liquid State of Solute Gas Liquid Solid Gas Solid State of Solvent Gas Liquid Solid Liquid Liquid Hydrogen in platinum Solid Gas Solid Example Air, natural gas Vodka, antifreeze 11.1 Chapter 11 | Slide 2 Copyright © Houghton Mifflin Company. All rights reserved. Solution Composition moles of solute Molarity (M) = liters of solution mass of solute Mass (weight) percent = 100% mass of solution molesA Mole fraction (A) = total moles in solution moles of solute Molality (m) = kilograms of solvent 11.1 Chapter 11 | Slide 3 Copyright © Houghton Mifflin Company. All rights reserved. Steps in the Dissolving Process 11.2 Chapter 11 | Slide 4 Copyright © Houghton Mifflin Company. All rights reserved. Concept Check Explain why water and oil (a long chain hydrocarbon) do not mix. In your explanation, be sure to address how ΔH plays a role. 11.2 Chapter 11 | Slide 5 Copyright © Houghton Mifflin Company. All rights reserved. The Energy Terms for Various Types of Solutes and Solvents H1 H2 H3 Hsoln Polar solvent, polar solute Large Large Large, Small negative Solution forms Polar solvent, nonpolar solute Small Large Small Large, positive No solution forms Nonpolar solvent, nonpolar solute Small Small Small Small Solution forms Nonpolar solvent, polar solute Large Small Small Large, positive No solution forms Outcome 11.2 Chapter 11 | Slide 6 Copyright © Houghton Mifflin Company. All rights reserved. In General • One factor that favors a process is an increase in probability. • Processes that require large amounts of energy tend not to occur. 11.2 Chapter 11 | Slide 7 Copyright © Houghton Mifflin Company. All rights reserved. Factors Affecting Solubility • Structural Effects: – Polarity • Pressure Effects: – Henry’s law • Temperature Effects: – Affecting aqueous solutions 11.3 Chapter 11 | Slide 8 Copyright © Houghton Mifflin Company. All rights reserved. Pressure Effects • Henry’s law: C = kP C = concentration k = constant P = partial pressure of gas solute above the solution • Amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution. 11.3 Chapter 11 | Slide 9 Copyright © Houghton Mifflin Company. All rights reserved. A Gaseous Solute 11.3 Chapter 11 | Slide 10 Copyright © Houghton Mifflin Company. All rights reserved. Temperature Effects (Aq Solns) • Although the solubility of most solids in water increases with temperature, the solubilities of some substances decrease with increasing temperature. • Predicting temperature dependence of solubility is very difficult. • Solubility of a gas in water typically decreases with increasing temperature. 11.3 Chapter 11 | Slide 11 Copyright © Houghton Mifflin Company. All rights reserved. The Solubilities of Several Solids as a Function of Temperature Chapter 11 | Slide 12 Copyright © Houghton Mifflin Company. All rights reserved. The Solubilities of Several Gases in Water Chapter 11 | Slide 13 Copyright © Houghton Mifflin Company. All rights reserved. An Aqueous Solution and Pure Water in a Closed Environment 11.4 Chapter 11 | Slide 14 Copyright © Houghton Mifflin Company. All rights reserved. Liquid/Vapor Equilibrium 11.4 Chapter 11 | Slide 15 Copyright © Houghton Mifflin Company. All rights reserved. Vapor Pressure Lowering: Addition of a Solute 11.4 Chapter 11 | Slide 16 Copyright © Houghton Mifflin Company. All rights reserved. Vapor Pressures of Solutions • Nonvolatile solute lowers the vapor pressure of a solvent. • Raoult’s Law: Psoln = ΧsolvPosolv Psoln = observed vapor pressure of soln Χsolv = mole fraction of solvent Posolv= vapor pressure of pure solvent 11.4 Chapter 11 | Slide 17 Copyright © Houghton Mifflin Company. All rights reserved. A Solution Obeying Raoult’s Law Chapter 11 | Slide 18 Copyright © Houghton Mifflin Company. All rights reserved. Nonideal Solutions • Liquid-liquid solutions where both components are volatile. • Modified Raoult’s Law: PTotal = ΧAPoA + ΧBPoB 11.4 Chapter 11 | Slide 19 Copyright © Houghton Mifflin Company. All rights reserved. Summary of the Behavior of Various Types of Solutions Interactive Forces Between Solute (A) and Solvent (B) Particles Hsoln T for Solution Formation Deviation from Example Raoult’s Law None Benzene(ideal toluene solution) A A, B B A B Zero Zero A A, B B < A B Negative (exothermic) Positive Negative Acetonewater A A, B B > A B Positive (endothermic) Negative Positive Ethanolhexane 11.4 Chapter 11 | Slide 20 Copyright © Houghton Mifflin Company. All rights reserved. Concept Check For each of the following solutions, would you expect it to be relatively ideal (with respect to Raoult’s Law), show a positive deviation, or show a negative deviation? a) Hexane (C6H14) and chloroform (CHCl3) b) Ethyl alcohol (C2H5OH) and water c) Hexane (C6H14) and octane (C8H18) 11.4 Chapter 11 | Slide 21 Copyright © Houghton Mifflin Company. All rights reserved. Colligative Properties • Depend only on the number, not on the identity, of the solute particles in an ideal solution: – Boiling-point elevation – Freezing-point depression – Osmotic pressure 11.5 Chapter 11 | Slide 22 Copyright © Houghton Mifflin Company. All rights reserved. Boiling-Point Elevation • Nonvolatile solute elevates the boiling point of the solvent. • ΔT = Kbmsolute ΔT = boiling-point elevation Kb = molal boiling-point elevation constant msolute = molality of solute 11.5 Chapter 11 | Slide 23 Copyright © Houghton Mifflin Company. All rights reserved. Boiling Point Elevation: Liquid/Vapor Equilibrium 11.5 Chapter 11 | Slide 24 Copyright © Houghton Mifflin Company. All rights reserved. Boiling Point Elevation: Addition of a Solute 11.5 Chapter 11 | Slide 25 Copyright © Houghton Mifflin Company. All rights reserved. Boiling Point Elevation: Solution/Vapor Equilibrium 11.5 Chapter 11 | Slide 26 Copyright © Houghton Mifflin Company. All rights reserved. Freezing-Point Depression • When a solute is dissolved in a solvent, the freezing point of the solution is lower than that of the pure solvent. • ΔT = Kfmsolute ΔT = freezing-point depression Kf = molal freezing-point depression constant msolute = molality of solute 11.5 Chapter 11 | Slide 27 Copyright © Houghton Mifflin Company. All rights reserved. Freezing Point Depression: Solid/Liquid Equilibrium 11.5 Chapter 11 | Slide 28 Copyright © Houghton Mifflin Company. All rights reserved. Freezing Point Depression: Addition of a Solute 11.5 Chapter 11 | Slide 29 Copyright © Houghton Mifflin Company. All rights reserved. Freezing Point Depression: Solid/Solution Equilibrium 11.5 Chapter 11 | Slide 30 Copyright © Houghton Mifflin Company. All rights reserved. Changes in Boiling Point and Freezing Point of Water 11.5 Chapter 11 | Slide 31 Copyright © Houghton Mifflin Company. All rights reserved. Exercise • You take 20.0 g of a sucrose (C12H22O11) and NaCl mixture and dissolve it in 1.0 L of water. The freezing point of this solution is found to be -0.426°C. Assuming ideal behavior, calculate the mass percent composition of the original mixture, and the mole fraction of sucrose in the original mixture. 11.5 Chapter 11 | Slide 32 Copyright © Houghton Mifflin Company. All rights reserved. Exercise • A plant cell has a natural concentration of 0.25 m. You immerse it in an aqueous solution with a freezing point of –0.246°C. Will the cell explode, shrivel, or do nothing? 11.5 Chapter 11 | Slide 33 Copyright © Houghton Mifflin Company. All rights reserved. Osmotic Pressure • Osmosis – flow of solvent into the solution through a semipermeable membrane. • π = MRT π = osmotic pressure (atm) M = molarity of the solution R = gas law constant T = temperature (Kelvin) 11.6 Chapter 11 | Slide 34 Copyright © Houghton Mifflin Company. All rights reserved. Osmotic Pressure 11.6 Chapter 11 | Slide 35 Copyright © Houghton Mifflin Company. All rights reserved. Osmosis 11.6 Chapter 11 | Slide 36 Copyright © Houghton Mifflin Company. All rights reserved. Exercise • When 33.4 mg of a compound is dissolved in 10.0 mL of water at 25°C, the solution has an osmotic pressure of 558 torr. Calculate the molar mass of this compound. 11.6 Chapter 11 | Slide 37 Copyright © Houghton Mifflin Company. All rights reserved.