Hydrogen ion and pH value

Combined hydrogen can form a hydrogen ion only if its compounds are dissolved in media able to solvate protons. The energy required for breaking the bond is provided by the solvation process  

The bare proton H never exists in condensed phases, it always occurs in the form of solvates (e.g. H30, R2OH ). The compounds which provide hydrogen ions in appropriate solutions or liquids, such as water, are called acids. 

Hydrogen ion in water is more correctly called the hydroxonium ion H30. Although we usually write H and talk about a hydrogen ion , we always assume that this ion is hydrated (H30 ) similarly as in the case of ions such as Fe , where it is known that hydrated particles [Fe(H20)e] are present in aqueous solutions. 

The dissociation equilibrium of water is characterized by the dissociation constant  

In diluted solutions the water activity can be considered to be constant (ohjO = const, 7H2O ) these can be combined into the constant K termed the ionic product of water 

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