The hydrogen ion formed from the ionization of pure water is highly reactive in nature which further reacts with the other molecules of pure water and forms hydronium ion (H3O+)
The Law of mass action for the self-ionization reaction of pure water at chemical equilibrium, the value of dissociation constant K is relationship between the concentration of reactants and product, for this ionization of pure water reaction; equation of dissociation constant K written as:
Here the dissociation of the pure water occurs in a very small extent; hence the concentration of un-dissociated water molecules, [H20], is considered as constant. Thus, the product [H20] gives another constant which is denoted as Kw and equation of Kw shown as:
Here, the constant (Kw), is termed as ionic product of water.
Concentrations H+ and OH- ions in pure water of product at a specific temperature is normally known as ionic product of water. The value of Kw (ionic product of water) rises with the rise of temperature, i.e., the concentration of H+ and OH- ions rises with temperature rises. Some constant values of KW at different temperature are shown in below table:
|Temperature (°C)||Value of Kw|
|0||0.11 x 10-14|
|10||0.31 x 10-14|
|25||1.00 x 10-14|
|100||7.50 x 10-14|
This interprets that at 25°C temperature; in 1 litre solution of pure water only 10-7 moles of water is present in the ionic form out of total moles of pure water (i.e. approximately 55.5 moles).
Similarly addition of the base leads to the rise in the concentration of the hydroxyl OH- ion or in other terminology it decreases the concentration of the hydrogen H+ion or hydroxonium H3O+ ion
In Neutral solution, the concentration of the H+ ion and OH- ion are equivalent to each other hence the value of the hydrogen ion and hydroxyl ion are the same.
|Concentration of [H+] ion||Nature of Water|
|Concentration of [OH-] ion||Nature of Water|