Advices For Studying Organic Chemistry

2.14E SOLUBILITIES

1. Solubility
   
   
   1. The energy required to overcome lattice energies and intermolecular or
      interionic attractions for the dissolution of a solid in a liquid comes from the
      formation of new attractions between solute and solvent.
   
   
   2. The dissolution of an ionic substance: hydrating or solvating the ions.
   
   
   3. Water molecules, by virtue of their great polarity and their very small, compact
      shape, can very effectively surround the individual ions as they freed from the
      crystal surface.
   
   
   4. Because water is highly polar and is capable of forming strong H-bonds, the
      dipole-ion attractive forces are also large.
   
   
   
   

H

O

H

H

O

H

H

O

H

H

O

H

H

O

H

H

O

H

H

O

H

H

O

H

H

O

H

H

O

H

− +

+ − + −

− +

+ −

− +

+ −

δ−

δ− δ− δ−

δ−

δ−

δ− δ−

δ−

δ−

δ+

δ+ δ+ + δ+

δ+

δ+

δ+ − δ+

δ+

δ+

Dissolution

Figure 2.9 The dissolution of an ionic solid in water, showing the hydration of
positive and negative ions by the very polar water molecules. The ions
become surrounded by water molecules in all three dimensions, not
just the two shown here.

2. “Like dissolves like”
   
   
   1. Polar and ionic compounds tend to dissolve in polar solvents.
   
   
   2. Polar liquids are generally miscible with each other.
   
   
   3. Nonpolar solids are usually soluble in nonpolar solvents.