equal to the concentration of OH - whereas in case of an aqueous solution of a substance which may behave as an acid (or) a base, the concentration of H O + will not be equal to [OH-] . We can understand this by considering the aqueous HCl as an example. In addition to the auto ionisation of water, the following equilibrium due to the dissociation of HCl can also exist. HCl+H2O H3O +Cl - In this case, in addition to the auto ionisation of water, HCl molecules also produces H O + ion by donating a proton to water and hence [H O ]>[OH - ] .
It means that the aqueous HCl solution is acidic. Similarly, in basic solution such as aqueous NH , NaOH etc….. [OH – ]>[H O + ]. Example .