H and Solubility

In a medium with a pH of less than 10.45, the solubility of Mg(OH)2 would increase. This follows from the fact that a lower pH indicates a higher [H ] and thus a lower [OH ], as we would expect from = [H ][OH ]. Consequently, [Mg ] rises to maintain the equilibrium condition, and more Mg(OH)2 dissolves. The dissolution process and the effect of extra H ions can be summarized as follows  

If the pH of the medium were higher than 10.45, [OH ] would be higher and the solubility of Mg(OH)2 would decrease because of the common ion (OH ) effect. 

The pH also influences the solubility of salts that contain a basic anion. For example, the solubility equilibrium for BaF2 is 

Because HF is a weak acid, its conjugate base, F , has an affinity for H.  

In an acidic medium, the high [H ] will shift the following equilibrium from left to right  

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