A simple calculation can show how small a fraction of water molecules
is dissociated. A concentration of 1.0 x 10-7 moles of
H+ per liter of water means that 1.0 x 10-7
moles of H2O has dissociated per 55.5 moles of water,
or one part in 0.56 x 10-9.
Approximately two water molecules out of every billion are dissociated
into H+ and OH- ions. The animation shows
what a tiny percentage that actually is...