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I was solving a question:
Which of the following liberate $\ce{O2}$ upon hydrolysis?
- $\ce{Pb3O4}$
- $\ce{KO2}$
- $\ce{Na2O2}$
- $\ce{Li2O2}$
The answer is no doubt $\ce{KO2}$ but if I am not wrong $\ce{Pb3O4}$ is insoluble so it doesn't undergo hydrolysis right and I would like to know the reason why $\ce{Pb3O4}$ is insoluble?
Most of metallic oxides are insoluble, as breaking of covalent bonds or the ionic lattice is not thermodynamicaly favorable.
Soluble exceptions mostly belong to electro-positive metal oxides ( together with peroxides and superoxides) from the first two groups of the periodic table, forming more or less soluble hydroxides. So it is not true dissolution.
Other exceptions are some oxides in high oxidation metal states, forming independent molecules, getting hydrated as acid anhydrides, like $\ce{Mn2O7, CrO3}$.
