Is water neutral in nature or amphoteric in nature? I understand it as an neutral compound in complex compounds, but I've been told that it is amphoteric, too.

  • $\begingroup$ Both. Having a pH of 7 it's by definition 'neutral'. But as a polar molecule and its ability to spontaneously dissociate into H and OH ions, water is often called the 'Universal Solvent' and can therefore be considered amphoteric. $\endgroup$ – docscience May 8 '15 at 14:07

$\ce{H2O}$ is a both a neutral molecule and an amphoteric molecule — the two are not mutually exclusive terms. An amphoteric molecule is simply one that can act as either an acid or a base, while a neutral molecule is one in which the total number of protons is equal to the number of electrons, such that there is zero net charge. Water can act as a Brønsted acid (i.e., an $\ce{H+}$ donor), as per the following reaction:

$\ce{H2O + NH2- -> OH- + NH3}$

However it can also act as a Brønsted base (i.e., an $\ce{H+}$ acceptor):

$\ce{H2O + HCl -> H3O+ + Cl-}$

When proton transfer is involved, as in the Brønsted definition of acids and bases, the more precise term is amphiprotic. However, water can also act as both a Lewis acid (an electron pair acceptor) and Lewis base (an electron pair donor). Notably, as a Lewis base, it is not limited merely to proton abstraction, but can act as a nucleophile with any number of electrophilic molecules.


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