Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Properties of Solutions Chapter 11.

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  • Slide 1
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 1 Properties of Solutions Chapter 11
  • Slide 2
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 2 Overview Introduce student to solution composition and energy of solution formation. Factor affecting solubilities will be discussed: structure, pressure and temperature effects. Vapor pressure of solutions, boiling point, freezing point affected by solute addition. Colligative properties of electrolyte solutions and colloids.
  • Slide 3
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 3 A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount
  • Slide 4
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 4 A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature. An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature. A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature. Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate.
  • Slide 5
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 5 Solution Composition 1.Molarity (M) = 2.Mass (weight) percent = 3.Mole fraction ( A ) = 4.Molality (m) =
  • Slide 6
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 6 Concentration Units The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. Percent by Mass % by mass = x 100% mass of solute mass of solute + mass of solvent = x 100% mass of solute mass of solution Mole Fraction (X) X A = moles of A sum of moles of all components
  • Slide 7
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 7 Concentration Units Continued M = moles of solute liters of solution Molarity (M) Molality (m) m = moles of solute mass of solvent (kg)
  • Slide 8
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 8 N = Number of equivalent liters of solution Normality (N) Acid-Base reaction: is the amount needed to accept one mole of H + Number of equivalent = mass Equivalent mass x 1 V Equivalent mass of H 2 SO 4 = MM 2 Equivalent mass of Ca(OH) 2 = MM 2
  • Slide 9
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 9 Redox reaction : is the amount needed to accept exactly one mole e - MnO 4 - + 5e - + 8H + Mn 2+ + 4H 2 O Equivalent mass of KMnO 4 = MM 5
  • Slide 10
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 10
  • Slide 11
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 11 What is the molality of a 5.86 M ethanol (C 2 H 5 OH) solution whose density is 0.927 g/mL? m =m = moles of solute mass of solvent (kg) M = moles of solute liters of solution Assume 1 L of solution: 5.86 moles ethanol = 270 g ethanol 927 g of solution (1000 mL x 0.927 g/mL) mass of solvent = mass of solution mass of solute = 927 g 270 g = 657 g = 0.657 kg m =m = moles of solute mass of solvent (kg) = 5.86 moles C 2 H 5 OH 0.657 kg solvent = 8.92 m
  • Slide 12
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 12 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
  • Slide 13
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 13 The formation of a liquid solution can be divided into three steps: (1) expanding the solute, (2) expanding the solvent, and (3) combining the expanded solute and solvent to form the solution.
  • Slide 14
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 14 HH < 0Exothermic Solution will occur
  • Slide 15
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 15 The driving factor that favor a process of solution formation is an increase in disorder
  • Slide 16
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 16
  • Slide 17
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 17 Factor Affecting Solubility 1.Structure 2.Pressure 3.Temperature
  • Slide 18
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 18 like dissolves like Two substances with similar intermolecular forces are likely to be soluble in each other. non-polar molecules are soluble in non-polar solvents CCl 4 in C 6 H 6 polar molecules are soluble in polar solvents C 2 H 5 OH in H 2 O ionic compounds are more soluble in polar solvents NaCl in H 2 O or NH 3 (l)
  • Slide 19
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 19 The molecular structures of (a) vitamin A (nonpolar, fat-soluble) and (b) vitamin C (polar, water-soluble). The circles in the structural formulas indicate polar bonds. Note that vitamin C contains far more polar bonds than vitamin A. Fat Soluble Hydrophobic Water Soluble Hydrophilic
  • Slide 20
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 20 Pressure Effects Pressure has little effect on solids and liquids. It increases the solubility of gases.
  • Slide 21
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 21 (a) A gaseous solute in equilibrium with a solution. (b) The piston is pushed in, increasing the pressure of the gas and number of gas molecules per unit volume. This causes an increase in the rate at which the gas enters the solution, so the concentration of dissolved gas increases. (c) The greater gas concentration in the solution causes an increase in the rate of escape. A new equilibrium is reached.
  • Slide 22
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 22
  • Slide 23
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 23 Henrys Law C = kP C = concentration of dissolved gas P = partial pressure of gaseous solute above the solution k = a constant The amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.
  • Slide 24
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 24 Henrys Law Applied for Dilute solutions Gases that do not dissociate or react with solvent: O 2 /waterApplied HCl/waterIs not applied
  • Slide 25
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 25 Temperature Effect on Gases The solubilities of several gases in water as a function of temperature at a constant pressure of 1 atm of gas above the solution.
  • Slide 26
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 26 The solubilities of several solids as a function of temperature. Temperature Effect on Gases
  • Slide 27
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 27 The Vapor Pressure of Solutions Solutions have different physical properties from pure solvent. Solutions of nonvolatile solutes differ from solutions of volatile solvents.
  • Slide 28
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 28 An aqueous solution and pure water in a closed environment. (a) Initial stage. (b) After a period of time, the water is transferred to the solution. Vapor pressure of pure water is higher VP of solution is lower
  • Slide 29
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 29 Raoults Law P soln = solvent P solvent P soln = vapor pressure of the solution 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. solvent = Moles of solvents Moles of solvent + Moles of solute
  • Slide 30
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 30 Note Solutions that obey Raoults Law are called Ideal Solutions. Can be used to determine the molar mass of unknown. For ionic compounds you should multiply by the total number of ions per molecule e.g. Na 2 SO 4 n = 3 x Na 2 SO 4
  • Slide 31
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 31 For a solution that obeys Raoult's law, a plot of P soln versus x solvent gives a straight line.
  • Slide 32
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 32 Non-Ideal Solutions When a solution contains two volatile components, both contribute to the total vapor pressure.
  • Slide 33
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 33 P A = X A P A 0 P B = X B P B 0 P T = P A + P B P T = X A P A 0 + X B P B 0
  • Slide 34
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 34 (a) ideal liquid-liquid solution by Raoult's law. (b) This solution shows a positive deviation from Raoult's law. (c) This solution shows a negative deviation from Raoult's law.
  • Slide 35
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 35
  • Slide 36
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 36 P T is greater than predicted by Raoultss law P T is less than predicted by Raoultss law Force A-B Force A-A Force B-B &
  • Slide 37
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 37 Colligative Properties of Non-Electrolyte Solutions Depend only on the number, not on the identity, of the solute particles in an ideal solution. 4 Boiling point elevation 4 Freezing point depression 4 Osmotic pressure
  • Slide 38
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 38 Boiling Point Elevation A nonvolatile solute elevates the boiling point of the solvent. T = K b m solute K b = molal boiling point elevation constant m = molality of the solute
  • Slide 39
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 39 Boiling-Point Elevation T b = T b T b 0 T b > T b 0 T b > 0 T b is the boiling point of the pure solvent 0 T b is the boiling point of the solution T b = K b m m is the molality of the solution K b is the molal boiling-point elevation constant ( 0 C/m)
  • Slide 40
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 40 Freezing Point Depression A nonvolatile solute depresses the freezing point of the solvent. T = K f m solute K f = molal freezing point depression constant m = molality of the solute
  • Slide 41
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 41 Freezing-Point Depression T f = T f T f 0 T f > T f 0 T f > 0 T f is the freezing point of the pure solvent 0 T f is the freezing point of the solution T f = K f m m is the molality of the solution K f is the molal freezing-point depression constant ( 0 C/m)
  • Slide 42
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 42 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.
  • Slide 43
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 43 Osmotic Pressure ( ) Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one. A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules. Osmotic pressure ( ) is the pressure required to stop osmosis. = MRT M is the molarity of the solution R is the gas constant T is the temperature (in K)
  • Slide 44
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 44 A tube with a bulb on the end that is covered by a semipermeable membrane.
  • Slide 45
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 45 The normal flow of solvent into the solution (osmosis) can be prevented by applying an external pressure to the solution. The minimum pressure required to stop the osmosis is equal to the osmotic pressure of the solution.
  • Slide 46
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 46 (a) A pure solvent and its solution (containing a nonvolatile solute) are separated by a semipermeable membrane through which solvent molecules (blue) can pass but solute molecules (green) cannot. The rate of solvent transfer is greater from solvent to solution than from solution to solvent. (b) The system at equilibrium, where the rate of solvent transfer is the same in both directions.
  • Slide 47
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 47 If the external pressure is larger than the osmotic pressure, reverse osmosis occurs. One application is desalination of seawater.
  • Slide 48
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 48 Reverse osmosis.
  • Slide 49
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 49 A cell in an: isotonic Solution (identical ) hypotonic Solution (water in) hypertonic Solution (water out)
  • Slide 50
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 50 Colligative Properties of Electrolyte Solutions T = imK = iMRT vant Hoff factor, i, relates to the number of ions per formula unit. NaCl = 2, K 2 SO 4 = 3
  • Slide 51
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 51 Boiling-Point Elevation T b = i K b m Freezing-Point Depression T f = i K f m Osmotic Pressure ( ) = iMRT Colligative Properties of Electrolyte Solutions
  • Slide 52
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 52 In an aqueous solution a few ions aggregate, forming ion pairs that behave as a unit: Ion Pairing
  • Slide 53
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 53 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.
  • Slide 54
  • Copyright2000 by Houghton Mifflin Company. All rights reserved. 54 A representation of two colloidal particles. The opposing charge repel and prevent precipitation The destruction of colloids is called coagulation, achieved by 1.Increasing temperature where colliding at...

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