Physical Properties of Solutions

1. Physical Properties of Solutions Chapter 13

2. 1. Most chemical reaction occurs when ions and molecular Interaction within solution phase 2. In Ch5 and Ch11, we mentioned the gas, liquid and solid properties. 3. In this chapter, we will focus on the molecular interaction in solution phase.

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

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. Crystallization Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate.

5. Three types of interactions in the solution process: • solvent-solventinteraction • solute-solute interaction • solvent-solute interaction Molecular view of the formation of solution DHsoln = DH1 + DH2 + DH3

6. “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 • CCl4 in C6H6 • polar molecules are soluble in polar solvents • C2H5OH in H2O • ionic compounds are more soluble in polar solvents • NaCl in H2O or NH3 (l) Solvation(溶合):Hydration is one kind of Solvation

7. moles of A XA = sum of moles of all components x 100% mass of solute x 100% = mass of solution mass of solute mass of solute + mass of solvent 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 = Mole Fraction(X)

8. moles of solute liters of solution moles of solute m = mass of solvent (kg) M = Concentration Units Continued Molarity(M) Molality(m)

9. moles of solute moles of solute m= m= moles of solute M = mass of solvent (kg) mass of solvent (kg) liters of solution 5.86 moles C2H5OH = 0.657 kg solvent What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is 0.927 g/mL? • 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 = 8.92 m

10. Selection of the concentration unit Mole fraction: used to calculate the partial pressure of gas or the vapor pressure of a solution. Molarity : Ease for preparing the solution Molality : When consider the temperature effect on solution using Molality will be better e.g.: 1.0 M solution prepared at 25 oC will change to 0.97M when temperature upto 45oC

11. solubility increases with increasing temperature solubility decreases with increasing temperature Temperature and Solubility Solid solubility and temperature

12. Fractional crystallization(分項結晶) Ex: 90 g KNO3 mixed with 10g NaCl, when cooled to 0oC, (90-12) g=78g KNO3 can be obtained from mixed solution

13. Temperature and Solubility O2 gas solubility and temperature solubility usually decreases with increasing temperature Heat west will strongly effect the environment due to the low solubility of O2 in water.

14. low P high P low c high c Pressure and Solubility of Gases The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law). c is the concentration (M) of the dissolved gas c = kP P is the pressure of the gas over the solution k is a constant for each gas (mol/L•atm) that depends only on temperature

16. Henry’s law • Henry’s Law can be explained as the impact frequency between gas molecular and liquid surface • The kinetic equilibrium: Vapor rate v.s Solubility • Most gas will follow Henry’s law, however, some gas is • excluded. EX: • Some reaction make the solubility much higher: • 1. NH3 + H2ONH4+ + OH- • 2.CO2+H2OH2CO3 • 3.Hb+4O2 Hb(O2)4 CO2 gas from soda

17. Colligative Properties 依數性質 Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. • The solution concentration is < 0.2 M • Vapor-Pressure Lowering • Boiling-Point Elevation • Freezing-Point Depression • Osmotic Pressure

18. = vapor pressure of pure solvent 0 P1 = X1 P 1 0 0 0 P 1 P 1 P 1 - P1 = DP = X2 Vapor-Pressure Lowering (蒸氣壓下降) X1= mole fraction of the solvent Raoult’s law 溶液中之溶劑分壓= 純溶劑蒸氣壓X 溶劑莫耳分率 If the solution contains only one solute: X1 = 1 – X2 X2= mole fraction of the solute 蒸氣壓下降與溶質莫耳數成正比

19. 0 0 0 0 PA = XA P A PB = XB P B PT = XA P A +XB P B Ideal Solution Volatile solution(both A and B are volatile) PT = PA + PB Ideal solution: =0 DHsoln 溶解熱

20. Nonideal gas: Case 1: The intermolecular forces between A and B are weaker than these between A or B molecular. Case 2: The intermolecular forces between A and B are stronger than these between A or B molecular.

21. Application: Fractional distillation (分餾結晶 or 蒸餾)

22. 0 DTb = Tb – T b 0 T b is the boiling point of the pure solvent 0 Tb > T b DTb = Kbm Boiling-Point Elevation T b is the boiling point of the solution DTb > 0 m is the molality of the solution Kb is the molal boiling-point elevation constant (0C/m) for a given solvent

23. 0 DTf = T f – Tf 0 T f is the freezing point of the pure solvent 0 T f > Tf DTf = Kfm Freezing-Point Depression T f is the freezing point of the solution DTf > 0 m is the molality of the solution Kf is the molal freezing-point depression constant (0C/m) for a given solvent EX: 灑鹽讓雪融化 EG 乙二醇抗凍劑

24. How to explain the freezing-point depression: A transition from the disordered state to the order state. For This to happen, more energy needs to be removed from the System. Because solution has greater disorder than the solvent, More energy need to removed. 亂度

26. 0 DTf = T f – Tf moles of solute m= mass of solvent (kg) = 3.202 kg solvent 1 mol 62.01 g 478 g x 0 Tf = T f – DTf What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is 62.01 g. DTf = Kfm Kf water = 1.86 oC/m = 2.41 m DTf = Kfm = 1.86 oC/m x 2.41 m = 4.48 oC = 0.00 oC – 4.48 oC = -4.48 oC

27. Osmotic Pressure (p) 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 (p) is the pressure required to stop osmosis. more concentrated dilute

28. Osmotic Pressure (p) time solution solvent High P Low P p = MRT Ex: 1.紅血球放在低滲溶液中, 使血球爆破。 2.用大量糖保存食物。(高滲溶液) M is the molarity of the solution R is the gas constant T is the temperature (in K)

29. A cell in an: isotonic solution hypotonic solution hypertonic solution

30. 海水淡化科技

32. Vapor-Pressure Lowering Boiling-Point Elevation DTb = Kbm 0 P1 = X1 P 1 Freezing-Point Depression DTf = Kfm p = MRT Osmotic Pressure (p) Colligative Properties Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 一般可由實驗方式量測溶液的待測濃度(m or M)

33. Free ions v.s bounded ion pair

34. actual number of particles in soln after dissociation van’t Hoff factor (i) = number of formula units initially dissolved in soln Colligative Properties of Electrolyte Solutions 考慮電解質的依數性質 0.1 m NaCl solution 0.1 m Na+ ions & 0.1 m Cl- ions Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles. 0.1 m NaCl solution 0.2 m ions in solution i should be 1 nonelectrolytes 2 NaCl CaCl2 3

35. Boiling-Point Elevation DTb = iKbm Freezing-Point Depression DTf = i Kfm p = iMRT Osmotic Pressure (p) Colligative Properties of Electrolyte Solutions

36. Colloids (膠體) Between homogenous solution and Nonhomogenous solution. A colloid is a dispersion of particles of one substance throughout a dispersing medium made of another Substance.

37. How to identify the solution and colloid? One way to distinguish a solution from A colloid is be the Tyndall effect. When a beam of light passes through A colloid, it is scattered by the dispersed Phase.

38. Hydrophilic and Hydrophobic Colloids • Hydrophilic: water-loving • Hydrophobic: water-fearing

39. E.g: 河流道出海口形成淤泥的現象

40. Along hydrocarbon tail that is nonpolar.

42. HW CH13 13.17 Calculate the molalities of these aqueous solutions: (a) 1.22 M sugar (C12H22O11) solution (density of solution = 1.12 g/mL), (b) 0.87 M NaOH solution (density of solution = 1.04 g/mL), (c) 5.24 M NaHCO3 solution (density of solution = 1.19 g/mL). 13.49 The vapor pressure of benzene is 100.0 mmHg at 26.1°C. Calculate the vapor pressure of a solution containing 24.6 g of camphor (C10H16O) dissolved in 98.5 g of benzene. (Camphor is a low-volatility solid.) 13.75 The osmotic pressure of 0.010 M solutions of CaCl2 and urea at 25°C are 0.605 atm and 0.245 atm, respectively. Calculate the van't Hoff factor for the CaCl2 solution.