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CH 11: Properties of Solutions

CH 11: Properties of Solutions. Describing Solutions – concentration units Energetics of solution formation Factors impacting solubility – P and T Colligative Properties of solutions BP elevation FP depression Osmotic pressure Vapor Pressure. Terms. Solution – homogeneous mixture

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CH 11: Properties of Solutions

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  1. CH 11: Properties of Solutions • Describing Solutions – concentration units • Energetics of solution formation • Factors impacting solubility – P and T • Colligative Properties of solutions • BP elevation • FP depression • Osmotic pressure • Vapor Pressure

  2. Terms • Solution – homogeneous mixture • Solvent – generally the larger component of the solution • Determines the physical state of the solution • Solute – generally the smaller component of the solution • Solute is dispersed in the solvent

  3. Solution Composition • Concentrated solution – relatively large amount of solute • Dilute solution – relatively small amount of solute

  4. Solution Composition • Unsaturated solution –solution with less than the maximum amount of solute that will normally dissolve at a given temperature • Saturated solution - solution with maximum amount of solute that will normally dissolve at a given temperature

  5. Solution Composition • Super-saturated solution - solution with more than the maximum amount of solute that will normally dissolve at a given temperature

  6. Concentration Units Molarity (M) = moles solute/Liters solution Molality (m) = moles solute/kg solvent Mass % = Mass solute/mass solution x100% Mole fraction (cA) = moles A/total moles

  7. Normality Normality (N) = # gram equivalent wt./L solution • Gew = mass of an acid or base that produces 1 mole of H+ or OH -1 Normality = Molarity x (# H+ or OH -1 /mol) • 1 M HCl = 1 N HCl • 1 M H2SO4 = 2 N H2SO4 For acid base titrations: (NAcid) (VAcid) = (NBase) (VBase)

  8. Practice! • Start by writing definitions for the concentration units M = m = Mass % = Mole fraction =

  9. Starting with Molarity Solution: • 3.75 M H2SO4 solution with a density of 1.23 g/mL Calculate: • Mass % • Molality • mole fraction of H2SO4

  10. Starting with Masses Solution: • A solution is made by combining 66.0 grams of acetone (C3H6 O) with 146.0 grams of water. • Solution has a density of 0.926 g/mL Calculate: • Molarity – need volume of solution • Mass % • Molality • Mole fraction of acetone

  11. Starting with Mass % Solution: • 35.4 % H3PO4 • Density of 1.20 g/mL Calculate: • Molarity • Molality • Mole fraction of H3PO4

  12. Starting with Molality Solution: • 2.50 m HClsolution • Density of 1.15 g/mL Calculate: • Molarity – need _______ • Mass % • Mole fraction of HCl

  13. Solution Formation Formation of a solution involves 3 steps • Separate the solute particles • expand the solute • Separate the solvent particles • Expand the solvent • Form the solution • Solute and solvent interact

  14. Solution Formation • Each step of solution formation involves energy and has a DH. DH1 = energy needed to separate the solute DH2 = energy needed to separate the solvent DH3 = energy released when solution forms

  15. Solution Formation DHsolution = DH1 +DH2 +DH3 Solutions form when the DHsolution is a small value – see page 504

  16. Factors Impacting Solubility • Structure – like dissolves like • #44 on page 533

  17. Factors Impacting Solubility • Pressure • Pressure has little impact on the solubility of liquids and solids • Pressure has a significant impact on the solubility of gases in a liquid • The higher the pressure of gaseous solute above a liquid the higher the concentration of the gas in the solution

  18. Henry’s Law • Henry’s Law: C = kP C = Concentration of dissolved gas k = solution specific constant P = partial P of the solute gas above the solution • What does Henry’s Law mean? • No calculations required. Page 506

  19. Temperature and Solubility • Temperature has variable effects on the amount of solid that will dissolve in an aqueous solution! • See figure 11.6 page 508 • Solutes will dissolve more rapidly at higher temperatures

  20. Temperature and Solubility • The solubility of a gas in water decreases as temperature increases. • See figure 11.7 on page 508 • Thermal pollution – read the story on page 510 when you get a chance

  21. Vapor Pressure of Solutions • See Raoult’s Law on page 510 • Psolution= csolvent P0solvent

  22. Colligative Properties • Colligative properties • properties of a solution that depend upon the amount of dissolved solute, not the identity of the solute. • Freezing point depression • Boiling point elevation • Osmotic Pressure • Note: I will be weaving section 11.7 and the van’t Hoff factor (i) into my consideration of these properties and not consider it separately.

  23. Colligative Properties • FP = Kf m i • BP = Kb m i See page 517 for needed constants

  24. Calculating the bp or fp of a solution • Calculating the molar mass of a solute from fp or bp data

  25. Osmotic Pressure • Osmotic Pressure (P) is often used to determine the molar mass of large biological molecules P = MRTi

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