Can H2O act as a lewis acid, lewis base, or both?

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Can H2O act as a lewis acid, lewis base, or both?

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Answer 1 · 2015-12-27T13:09:43

Water can act as both a Lewis acid and a Lewis base.

Explanation:

Water is amphoteric: this means that it can act both as an acid and as a base. The reason for this is that water is self-ionising. Observe the following equation:

$2 H_{2} O ⇌ H_{3} O^{+} + {OH}^{-}$ $color(red)(2)"H"_2"O" rightleftharpoons "H"_3"O"^+ + "OH"^-$

Source: Wikipedia

This reaction is reversible, because the hydronium ion ( $H_{3} O^{+}$ $"H"_3"O"^+$ ) is a strong acid and the hydroxide ion ( ${OH}^{-}$ $"OH"^-$ ) is a strong base, they will react together in the opposite direction to form water. These reactions occur according to the ionisation constant of water, $P_{w}$ $"P"_w$ , which is $1.0 \cdot 10^{- 14}$ $1.0 * 10^(-14)$ at room temperature.

As mentioned above, since the hydronium and hydroxide ions are quite strong acids and bases, respectively, the self-ionisation of water allows it to function both as a Lewis acid and as a Lewis base via protonation.

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Can H2O act as a lewis acid, lewis base, or both?

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