Ionic Product of Water:

Water containing a certain proportion of hydrogen and hydroxyl ions, therefore conductometric methods may be used to determine the ionic product of water. Ionisation of water is given by following equation:

H₂O  ⇔   H⁺ + OH ^-

An equilibrium constant within terms of activity can be written as

K_w = a_H+ a_OH- /aH₂O

but, since, for pure water,  a _H2O= 1, thus

K_w    = a_H+  a_{OH -} ≈ [H ⁺ ] [OH ^- ]

where K_w is called the ionic product of water. K_w can be determined from conductivity measurements as follows.

If the concentration of ionized water is c, after that

c_{H +}  = c_OH-   = c