Is Oil Miscible in Water?Oil:Nonpolar(London Forces)Water:Polar(Hydrogen Bonding)Oil/Water: Nonpolar/Polar(Dipole-Induced Dipole)So: ∆H1+ ∆H2= large (+)∆H3= very small (-)∆Hsol’n= Large (+)(>0)üThus: oil and water are NOT miscible3Miscible Is Methyl Alcoholin Water?Methyl Alcohol:Polar(Hydrogen Bonding)Water:Polar(Hydrogen Bonding)Alcohol/Water: Polar/Polar(Hydrogen Bonding)So: ∆H1+ ∆H2= large (+)∆H3= large(-)∆Hsol’n= small (+/-)? Why ismethyl alcohol miscible in water?42
Will NaCl Dissolve In Water?NaCl(s):Strong Ionic BondNaCl(s) →Na+(g) + Cl-(g) ∆H1= 786 kJ/molHH2O and NaCl/H2O:Ion-Dipole/H-Bonding2O(l) + Na+(g) + Cl-(g) →Na+(aq) + Cl-(aq)∆Hhyd= ∆H2+ ∆H3= -783 kJ/molSo: ∆Hsol’n= 786+ (-783) = +3 kJ/mol? So whydoes NaCl dissolve in water?5Enter: Entropy•“Nature favors disorder”•be favoredProcesses which increase disorder(spontaneous)tend to NaCl (s) →Na+(aq) + Cl-(aq) increased disorder•Since ∆Hsolnis very small, process is said to be:Entropically-Driven63
Structure andSolubilityØIf solute and solvent are very different: IM Forcesnot solubleVitamin AØIf solute and solvent are similar:IM ForcessolubleØ“Like dissolves like”Vitamin C74
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