Chemistry(CH3COOH)

In CH3COOH, the functional group is -COOH. It can be ionized to
-COO(^ -) + H(^+).
For -COO(^-), we usually say that C is double bonded to an O, and single bonded to another O(^ -). However, in reality, the two bondings are in reasonance. That means the double bond and the negative charge will "shift" between the two O atoms.
O=C-O(^ -) <-------> O(^ -)-C=O.
Therefore, the negative charge is shared by the two O atoms, and hence stablizing the ion. This makes ionization must more probable.

On the other hand, in CH3CH2OH, the functional group is -OH. In fact there will be a very small amount of ethanol molecules ionized
CH3CH2OH <--------> CH3CH2O(^ -) + H(^+)
However, since in this case, there are no other atoms to share the negative charge on the O atom, the ion is very unstable, and hence the equilibrium is very much on the left hand side. Therefore, practically speaking, CH3CH2OH is not able to ionize.

2008-01-26 14:57:17 補充：
Since practically none of ethanol molecules is ionized, ethanol does not increase nor decrease the amount of H+ ions and OH- ions in the solution. Hence it is neutral.

The dissociation of ethanoic acid and ethanol is depends on the stability of cprrespond ing conjugate base. The conjugate baes of ethanoic acid (i.e. ethanoate ions) is more stable due to resonance effect, the negatively charge in ethanoate ions can delocalize, so the conjugate base can formed more stable. While the conjugate base of ethanol is less stable because the negatively charge in conjugate base cannot spread around as no resonance effect, so ethanol dissolved in water to form unstable conjugate ion.

Since the solubility increses as the stability of conjugate ion increases, hence ethanoic acid can easily ionize in water while ethanol cannot.

Why the ethanoic acid have resonance effect while ethanol does not have?
Carboxyl group has multiple bond, so the resonance effect can be occured.