H3o oh

x flr

where pKw is the negative logarithm of the dissociation constant for water, Kw. Kw is derived from consideration of the equilibrium

tH2O Lh2°J2

The concentration of molecular water is considered to be virtually constant for dilute aqueous solutions. Therefore

where one molecule of water is behaving as the weak acid or base and the other is behaving as the solvent. Then where the dissociation constant for water (the ionic product) now incorporates the term for molecular water and has the values given in Table 3.7.

Table 3.7 Ionic product for water

Temperature (0C)

Kw X 1014


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