How can water be a lewis base?

1 Answer
Mar 11, 2014

Water can be a Lewis acid AND base.

Water (#H_2O#) is amphoteric, meaning that it can "self ionize".
#H_2O# + #H_2O# = #H_3O^+# + #OH^-#

One of the water molecules acts as a Lewis acid (#H_3O^+#) and one acts as a Lewis base (#OH^-#)

The Lewis definition of a base (lewis base) is that it donates an electron pair, while a Lewis acid accepts it. When water is ionized, the #OH^-# may donate electrons to another acid besides the #H_3O^+# ion, therefore reacting with it.