How does water react to form ions?

1 Answer
anor277
Dec 29, 2015

Water undergoes autoprotolysis. The reaction is given in the next section.

Explanation:

#H_2O rightleftharpoons H^(+) + HO^-#.

Alternatively:

#2H_2O rightleftharpoons H_3O^(+) + OH^-#

Reaction (ii) is a bit more common these days. What we conceive to be the acidium ion, #H^+ or H_3O^+#, is actually a cluster of water atoms (4-5) with an extra proton, i.e. #H_9O_4^+#.

In any case the equilibrium is known for standard conditions (#1# #atm#, #298K#), and the ion product, #K_w# #=# #[H_3O^+][HO^-]# #=# #10^(-14)#.

Under non-standard conditions (i.e. > #298K#), would you expect #K_w# to increase or decrease? Why?

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