Acidity of Cations in Aqueous Solution

Many positive ions exhibit acidic behavior in solution. For example, Fe in water forms an acidic solution, with yellow or brown iron species formed by reactions such as 

In less acidic (or more basic) solutions, hydroxide or oxide bridges between metal atoms form, the high positive charge promotes more hydrogen ion dissociation, and a large aggregate of hydrated metal hydroxide precipitates. A possible first step in this process is 

At the highly charged extreme, the free metal cation is no longer a detectable species. Instead, ions such as permanganate (MnOq ), chromate (Cr04 ), uranyl (UO2 ), dioxovanadium (VOi ), and vanadyl (VO ) are formed, with oxidation 

In concentrated acid, the dichromate ion is formed by loss of water  

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