# How do classify the behaviour of water as an acid?

May 25, 2017

Water is an $\text{amphoteric species}$ according to the $\text{Bronsted Lowry concept.}$

#### Explanation:

According to the $\text{Lewis concept}$, water is also amphoteric.

A Lewis acid is defined as an electron-pair acceptor; and a Lewis base in an electron pair donor. Water's dual classification can be appreciated from the autoprotolysis reaction of water:

$2 {H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + H {O}^{-}$

While this (carefully measured!) equilibrium lies strongly to the left, water has clearly acted as a Lewis base to give the $\text{hydronium ion}$, and as a Lewis acid to give the $\text{hydroxide ion}$.