27/11/2014
Chemical changes will change IMFs, solubility, extraction strategy. Consider this data.
molecule
structure
IMFs
ionic, some dipole,
H‐bonding?
sodium benzoate
solubility
H2 O
CHCl3
63 g/L
zero
sodium benzoate
benzoic acid
H 2O
CHCl3
a) yes b) no
sodium
benzoate
benzoic acid
structure
ionic, some dipole,
H‐bonding?
solubility
H2 O
CHCl3
63 g/L
zero
H 2O
H‐bonding,
some dipole, 3.4 g/L 185 g/L
large dispersion
CHCl3
a) H2O b) CHCl3
No. H2O: highly polar, H‐bonding. CHCl3: weakly polar, no H‐bonding. H2O and CHCl3 are immiscible.
molecule
IMFs
Add sodium benzoate. Is the sodium benzoate in the H2O or the CHCl3?
Add CHCl3 (d = 1.5 g/cm3) to H2O (d = 1.0 g/cm3).
Do the H2O and CHCl3 mix together?
1
structure
benzoate
H‐bonding,
some dipole, 3.4 g/L 185 g/L
large dispersion
benzoic acid
molecule
IMFs
ionic, some dipole,
H‐bonding?
2
Ionic salt has strong attractive forces with highly polar and H‐bonding H2O, so higher solubility with H2O.
solubility
H2 O
CHCl3
63 g/L
zero
H‐bonding,
some dipole, 3.4 g/L 185 g/L
large dispersion
H2O HCl NaCl
benzoate
CHCl3
benzoic acid
Add HCl(aq), a far stronger acid than benzoic acid: HCl + RCO2–Na+ Î NaCl + RCO2H.
In what form and where is the product? a) benzoate in H2O b) benzoate in CH3Cl
c) benzoic acid in H2O d) benzoic acid in CH3Cl 3
Product is neutral, with large dispersion forces, and so less attractive to H2O. It has higher solubility in CH3Cl.
1