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CVEN 4424 Environmental Organic Chemistry

CVEN 4424 Environmental Organic Chemistry . Lecture 6 – Aqueous Solubility. Announcements. Reading Chapter 5, Aqueous solubility Problem sets PS 2 due today PS 3 out today, due next Thursday Office hours Tuesday, 12:30-2, my office Wednesday, 11-12 am, ECES 131

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CVEN 4424 Environmental Organic Chemistry

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  1. CVEN 4424Environmental Organic Chemistry Lecture 6 – Aqueous Solubility

  2. Announcements • Reading • Chapter 5, Aqueous solubility • Problem sets • PS 2 due today • PS 3 out today, due next Thursday • Office hours • Tuesday, 12:30-2, my office • Wednesday, 11-12 am, ECES 131 • Wednesday, 3-5 pm, ECES 131 (TA Brett)

  3. Aqueous Solubility  • Another phase change • vapor pressure: • pure solid  gas (ideal) • pure liquid  gas (ideal) • aqueous solubility • pure solid  “liquid” in water (mixed, non-ideal) • pure liquid  liquid in water (mixed, non-ideal) • pure gas  “liquid” in water (mixed, non-ideal) • solubility (Cwsat) at specified T and p

  4. Aqueous Solubility

  5. Aqueous Solubility w L Solubility of an organic liquid

  6. Aqueous Solubility w L • Solubility of an organic liquid • assumptions about organic phase • xL 1 (essentially no water in organic phase) • L = 1 (pure liquid; ideal interactions)

  7. Aqueous Solubility w L • Solubility of an organic liquid • assumptions about organic phase • xL 1 (essentially no water in organic phase) • L = 1 (pure liquid; ideal interactions)

  8. Aqueous Solubility ideal mixing non-ideal interactions • Solubility of an organic liquid • already liquid; does not have to melt • ideal mixing, RTlnxw • wSideal increases; change in molar volume • non-ideal interactions, RTlnw • enthalpy cost, wHE, and entropy cost, wSE • proportional to solute size  cavity in water

  9. solid fusH fusS Aqueous Solubility water liquid wHE wSE wSideal

  10. Aqueous Solubility fusG: melting costs - need more heat, fusH - further increase in entropy, fusS • Solubility of an organic solid • pure solid  pure liquid (melting) • pure liquid  water (dissolution)

  11. Aqueous Solubility What is the solubility of a Twinkie?(an organic solid?)

  12. gas -vapH -vapS Aqueous Solubility solid fusH fusS water liquid wHE wSE wSideal

  13. Aqueous Solubility condG: condensation “income” - removing heat, condH - decreasing entropy, condS • Solubility of an organic gas • pure gas  pure liquid (condensation) • pure liquid  water (dissolution) • p = 1 bar

  14. Aqueous Solubility Excess enthalpy of solubility wH2 (+) wH1(+) wH3(-) wH4(-) wHcav wHice

  15. fusH(+) Aqueous Solubility Excess enthalpy of solubility wH2 (+) wH1(+) wH3(-) wH4(-) wHcav wHice

  16. fusH(+) -vapH(-) Aqueous Solubility Excess enthalpy of solubility wH2 (+) wH1(+) wH3(-) wH4(-) wHcav wHice

  17. Aqueous Solubility * at saturation or dilute condition

  18. Aqueous Solubility fusS(+) Excess entropy of solubility wScav(-) wSideal(+) wSice(-) -vapS(-)

  19. Aqueous Solubility * at saturation or dilute condition

  20. gas -vapH -vapS Aqueous Solubility solid fusH fusS water liquid wHE wSE wSideal

  21. Aqueous Solubility • Rank the following compounds by aqueous solubility from highest to lowest.benzene ethylbenzenetoluene p-xyleneA. ethylbenzene > p-xylene > toluene > benzeneB. benzene > toluene > ethylbenzene > p-xyleneC. benzene > toluene > p-xylene  ethylbenzene

  22. Aqueous Solubility • Rank the following compounds by aqueous solubility from highest to lowest.benzene ethylbenzenetoluene p-xyleneA. ethylbenzene > p-xylene > toluene > benzeneB. benzene > toluene > ethylbenzene > p-xyleneC. benzene > toluene > p-xylene  ethylbenzene Cwsat 0.022 M 0.0060 M 0.0016 M 0.0017 M

  23. Aqueous Solubility * at saturation or dilute condition

  24. Aqueous Solubility • At equilibrium (wG = 0)

  25. Aqueous Solubility • At equilibrium (wG = 0)

  26. Aqueous Solubility • At equilibrium (wG = 0)

  27. Aqueous Solubility • Activity coefficient • for low solubility compounds: • for high solubility compounds • solubility defined two ways: • “low solubility” as w > 100 • “high solubility” as volume fraction >0.01

  28. Aqueous Solubility high activity coefficient low solubility  wsat Cwsat low activity coefficient high solubility 

  29. water Aqueous Solubility gas liquid • Relate w to other properties • from pure liquid to vapor • described by pL* • from vapor to water • size of cavity • molar volume of solute • solute-water interactions • van der Waals • hydrogen bonding

  30. Aqueous Solubility vdW forces size H-bond descriptor for H-acceptor (Table 4.3) vapor pressure of solute as a liquid (bar) molar volume of solute as a liquid H-bond descriptor for H-donor (Table 4.3) dipolarity/ polarizability descriptor (Table 5.5) refractive index of solute Relate w to other properties (Eqn. 5-22)

  31. Aqueous Solubility • Temperature dependence • liquid • small DwHE • small temperature effect • solid • small DwHE, large DfusH • large temperature effect • gas • small DwHE, large DcondH • large temperature effect

  32. Aqueous Solubility • Gas • Cwsatincreaseswith decreasing temperature • Liquid • not much  • Solid • Cwsat decreaseswith decreasing temperature

  33. Aqueous Solubility • Liquid • slope iswHE/R over T range of interest • slope very small • slope not constant • wHE is very small, sometimes +, sometimes –(see Table 5.3)

  34. Aqueous Solubility • Solid • slope is wH/R = (fusH +wHE)/R • Usually,fusH > wHE

  35. Aqueous Solubility • Gas • slope is wH/R = (-vapH + wHE)/R • Usually, -vapH > wHE

  36. Aqueous Solubility Na+ • Salt in water • “electrostriction” • water forms hydration shells around ions • less water available for compound to dissolve into • “Salting out” • decreases solubility of nonpolar organic compounds

  37. Aqueous Solubility • Setschenow equation • Setschenow constant KS • compound-specific (increases with decreasing Cwsat) • salt-specific (increases with increasing ion hydration) • total molar salt concentration [salt]t • single salt or mixture of salts (e.g., seawater) (Eqn. 5-27)

  38. Aqueous Solubility • Example: pyrene “salting out” of seawater • Cwsat (25C) = 10-6.16 M • KS = 0.30 (Table 5.7 for seawater) • [salt]T  0.5 M • {[cations (M)] + [anions (M)]}/2

  39. Aqueous Solubility • Example: pyrene • seawater reduces solubility by about 29%

  40. Aqueous Solubility pyrene in pure water pyrene in 20% methanol solution • Co-solvents in water • high solubility organic compounds • replace water in cavity around nonpolar organic compound • Increase solubility • more favorable interactions with nonpolar organic compound

  41. Aqueous Solubility (Eqn. 5-33) • Estimate solubility in co-solvent mixture • il activity coefficient in co-solvent/water mix • iw activity coefficient in pure water • ic “co-solvency power” (depends on fv) • fractional volume of co-solvent in water fv

  42. Aqueous Solubility • Example (see Illustrative Example 5.5) • What is the solubility of naphthalene in a 20% acetone/water solution at 298 K? • activity coefficient of naphthalene (solid)

  43. Aqueous Solubility • Example • activity coefficient of naphthalene (solid) • Cwsat = 10-3.60 M • Vw = 0.018 L mol-1 • vapor pressure ratio

  44. Aqueous Solubility • Example • activity coefficient of naphthalene (solid) • vapor pressure ratio •  = 0 (no SP3, no SP2, 1 RING) •  = 4 (2 planes of rotational symmetry) • Tm = 80.2 C = 353.4 K

  45. Aqueous Solubility • Example • activity coefficient of naphthalene (solid) • ic = 6.5 (Table 5.8) • fv = 0.2

  46. Aqueous Solubility • Example • solubility: naphthalene in 20% acetone/water

  47. Aqueous Solubility • Organic liquid mixtures • petroleum – gasoline, oil, kerosene • coal tar • PCBs – Arochlor

  48. Aqueous Solubility • Organic liquid mixtures • org mix  1 to 5 • xorg mix • need average mw of organic liquid mixture • e.g., coal tar150 g mol-1 • no melting costs • compound is already in liquid phase in organic mixture

  49. Aqueous Solubility Organic liquid mixtures example: What concentration of benzene should we find in water in equilibrium with gasoline containing benzene at a concentration of 1 vol%?

  50. Aqueous Solubility Benzene in water in equilibrium with gasoline containing 1 vol% benzene? Need estimates for and

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