Hòa tan Fe3O4 vào dung dịch H2SO4 (loãng, dư), thu được dung dịch X

- Dung dịch X chứa Fe²⁺, Fe³⁺, H⁺ dư, SO₄^2-.

\(2KMn{O_4} + 10FeS{O_4} + 8{H_2}S{O_4} \to 5F{e_2}{(S{O_4})_3} + {K_2}S{O_4} + 2MnS{O_4} + 4{H_2}O\)

\(\begin{array}{l} 2F{e^{2 + }} + C{l_2} \to 2F{e^{3 + }} + 2C{l^ - }\\ {H^ + } + O{H^ - } \to {H_2}O\\ F{e^{2 + }} + 2O{H^ - } \to Fe{(OH)_2}\\ F{e^{2 + }} + 3O{H^ - } \to Fe{(OH)_3} \end{array}\)

\(2{H^ + } + CO_3^{2 - } \to C{O_2} + {H_2}{\rm{O}};\;F{e^{3 + }} + CO_3^{2 - } + 2{H_2}O \to Fe{(OH)_3} + C{O_2} + {H^ + }\;;\;F{e^{2 + }} + CO_3^{2 - } \to FeC{O_3}\)

\(\begin{array}{l} Cu + 2F{e^{3 + }} \to C{u^{2 + }} + 2F{e^{2 + }}\\ 3F{e^{2 + }} + 4{H^ + } + N{O_3}^ - \to 3F{e^{3 + }} + NO + 2{H_2}O \end{array}\)