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Properties of Solutions Chapter 11

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Solutions... the components of a mixture are uniformly intermingled (the mixture is homogeneous).

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Solution Composition 1.Molarity (M) = 2.Mass (weight) percent = 3.Mole fraction ( A ) = 4.Molality (m) =

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Molarity Calculations

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Mass % Calculations

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Mole Fraction

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Molality Calculations

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Molarity & Molality For dilute solutions, molarity (M) and molality(m) are very similar. In previous example, M = M and m = m.

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Normality Acid-Base Equivalents = (moles) (total (+) charge) Redox Equivalents = (moles)(# e - transferred)

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Normality Calculations.250 M H 3 PO 4 =______N N = M(total(+) charge) N = (0.250)(3) N = N H 3 PO 4

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Concentration & Density Calculations See Example 11.2 on pages Know how to do this problem!!

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Steps in Solution Formation Step 1 -Expanding the solute (endothermic) Step 2 -Expanding the solvent (endothermic) Step 3 -Allowing the solute and solvent to interact to form a solution (exothermic) H soln = H step 1 + H step 2 + H step 3 H soln = H step 1 + H step 2 + H step 3

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Three steps of a liquid solution: 1) expanding the solute, 2) expanding the solvent, & 3) combining the expanded solute and solvent to form the solution.

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a) H soln is negative and solution process is exothermic. b) H soln is positve and solution process is endothermic.

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Processes that require large amounts of energy tend not to occur. Solution process are favored by an increase in entropy.

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Structure & Solubility Like dissolves like. Hydrophobic --water-fearing. Fat soluble vitamins such as A, D, E, & K. Hydrophilic --water-loving. Water soluble vitamins such as B & C. Hypervitaminosis--excessive buildup of vitamins A, D, E, & K in the body.

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Henrys Law P = kC P = partial pressure of gaseous solute above the solution C = concentration of dissolved gas k = a constant The amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

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Solubility of several solids as a function of temperature.

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The solubility of various gases at different temperatures.

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When an aqueous solution and pure water are in a closed environment, the water is transferred to the solution because of the difference in vapor pressure.

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Raoults Law P soln = solvent P solvent P soln = vapor pressure of the solution solvent = mole fraction of the solvent solvent = mole fraction of the solvent P solvent = vapor pressure of the pure solvent The presence of a nonvolatile solute lowers the vapor pressure of a solvent.

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Raoults Law Calculations Sample Exercise 11.6 on page 532. Na 2 SO 4 forms 3 ions so the number of moles of solute is multiplied by three. P soln = water P water P soln = (0.929)(23.76 torr) P soln = P soln = 22.1 torr

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Vapor pressure for a solution of two volatile liquids. a) Ideal(benzene & toluene) -- obeys Raoults Law, b) Positive deviation (ethanol & hexane) from Raoults Law, & c) Negative deviation (acetone & water). Negative deviation is due to hydrogen bonding.

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Liquid-Liquid Solutions P total = P A + P B = A P o A + B P o B = A P o A + B P o B

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Raoults Law Calculations Sample Exercise 11.7 on page 535. A = n A /(n A +n C ) A = n A /(n A +n C ) A = mol/(0.100 mol mol) A = mol/(0.100 mol mol) A = C = A = C = P total = A P o A + C P o C P total = (0.500)(345 torr) + (0.500)(293 torr) P total = P total = 319 torr

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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

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Phase diagrams for pure water and for an aqueous solution containing a nonvolatile solute -- liquid range is extended for the solution.

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Boiling Point Elevation A nonvolatile solute elevates the boiling point of the solvent. The solute lowers the vapor pressure of the solution. T = K b m solute i T = K b m solute i K b = molal boiling point elevation constant m = molality of the solute i = vant Hoff factor ( # ions formed)

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Boiling Point Calculations Sample Exercise 11.8 on page 537. T = K b m solute i T = K b m solute i m solute = T/(K b i) m solute = (0.34 C o )/[(0.51 C o kg/mol)(1)] m solute = 0.67 mol/kg

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Boiling Point Calculations (Continued) m solute = n solute / kg solvent n solute = m solute kg solvent n solute = (0.67 mol/kg)( kg) n solute = 0.10 mol

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Boiling Point Calculations (Continued) n = m/M M = m/n M = g/0.10 mol M = 180 g/mol

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Freezing Point Depression A nonvolatile solute depresses the freezing point of the solvent. The solute interferes with crystal formation. T = K f m solute i T = K f m solute i K f = molal freezing point depression constant m = molality of the solute i = vant Hoff factor ( # ions formed)

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Freezing Point Calculations Sample Exercise on page 539. T = K f m solute i T = K f m solute i m solute = T/(K f i) m solute = (0.240 C o )/[(5.12 C o kg/mol)(1)] m solute = 4.69 x mol/kg

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Freezing Point Calculations (Continued) m solute = n solute / kg solvent n solute = m solute kg solvent n solute = (4.69 x mol/kg)( kg) n solute = 7.04 x mol

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Freezing Point Calculations (Continued) n = m/M M = m/n M =.546 g/7.04 x mol M = 776 g/mol

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Osmotic Pressure Osmosis: The flow of solvent into the solution through the semipermeable membrane. Osmotic Pressure: The excess hydrostatic pressure on the solution compared to the pure solvent.

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Due to osmotic pressure, the solution is diluted by water transferred through the semipermeable membrane. The diluted solution travels up the thistle tube until the osmotic pressure is balanced by the gravitational pull.

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Osmosis The solute particles interfere with the passage of the solvent, so the rate of transfer is slower from the solution to the solvent than in the reverse direction.

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a) The pure solvent travels at a greater rate into the solution than solvent molecules can travel in the reverse direction. b) At equilibrium, the rate of travel of solvent molecules in both directions is equal.

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Osmotic Pressure = MRT = MRT = osmotic pressure (atm) = osmotic pressure (atm) M = Molarity of solution R = Latm/molK T = Kelvin temperature

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Osmotic Pressure Calculations Sample Exercise on pages = MRT = MRT M = /RT M = (1.12 torr)(1 atm/760 torr)/[( Latm/molK)(298K)] M = 6.01 x mol/L

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Osmotic Pressure Calculations Continued Molar Mass = (1.00 x g/1.00 mL)(1000 mL/1 L)(1 L/6.01 x mol) = 1.66 x 10 4 g/mol protein

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Crenation & Lysis Crenation-solution in which cell is bathed is hypertonic (more concentrated)-cell shrinks. Pickle, hands after swimming in ocean. Meat is salted to kill bacteria and fruits are placed in sugar solution. Lysis-solution in which cell is bathed is hypotonic (less concentrated)-cell expands. Intravenous solution that is hypotonic to the body instead of isotonic.

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If the external pressure is larger than the osmotic pressure, reverse osmosis occurs. One application is desalination of seawater.

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Colligative Properties of Electrolyte Solutions T = mKi T = mKi = MRTi = MRTi vant Hoff factor, i, relates to the number of ions per formula unit. NaCl = 2, K 2 SO 4 = 3

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Electrolyte Solutions The value of i is never quite what is expected due to ion-pairing. Some ions stay linked together--this phenomenon is most noticeable in concentrated solutions.

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Osmotic Pressure Calculation for Electrolyte Sample Exercise on page 548. Fe(NH 4 ) 2 (SO 4 ) 2 produces 5 ions. = MRTi = MRTi i /MRT i = 10.8 atm/[(0.10 mol/L)( Latm/molK)(298 K)] i = 4.4

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Colloids Colloidal Dispersion (colloid): A suspension of tiny particles in some medium. aerosols, foams, emulsions, sols Coagulation: The addition of an electrolyte, causing destruction of a colloid. Examples are electrostatic precipitators and river deltas.

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The eight types of colloids and examples of each.

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Tyndall Effect The scattering of light by particles of a colloid is called the Tyndall Effect. Which of the glasses below contains a colloid?

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Calorimeter Problem Add this problem to the Chapter 11 set of problems. KNOW how to work this problem--show the appropriate formula!! When 8.50 g of sodium nitrate is dissolved in 600. g of water, the temperature of the solution rises C o. What is the molar heat of solution for sodium nitrate?

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