Cho Fe3O4 vào dung dịch H2SO4 loãng dư thu được dung dịch X. Hãy cho biết trong các hoá chất sau: KMnO4, Cl2, NaOH, Na2CO3, CuSO4, Cu, KNO3 thì dung dịch X tác dụng được với bao nhiêu chất? A. 4. B. 5. C. 6. D. 7.
Đáp án đúng: D 7. $\begin{array}{l}\text{F}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}}\text{+4}{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\xrightarrow{{}}\text{FeS}{{\text{O}}_{\text{4}}}\text{+F}{{\text{e}}_{\text{2}}}{{\text{(S}{{\text{O}}_{\text{4}}}\text{)}}_{\text{3}}}\text{+4}{{\text{H}}_{\text{2}}}\text{O}\\\text{5F}{{\text{e}}^{\text{2+}}}\text{+MnO}_{\text{4}}^{\text{-}}\text{+8}{{\text{H}}^{\text{+}}}\xrightarrow{{}}\text{5F}{{\text{e}}^{\text{3+}}}\text{+M}{{\text{n}}^{\text{2+}}}\text{+4}{{\text{H}}_{\text{2}}}\text{O}\\\text{2F}{{\text{e}}^{\text{2+}}}\text{+C}{{\text{l}}_{\text{2}}}\xrightarrow{{}}\text{2F}{{\text{e}}^{\text{3+}}}\text{+2C}{{\text{l}}^{\text{-}}}\\\text{F}{{\text{e}}^{\text{2+}}}\text{,}\,\text{F}{{\text{e}}^{\text{3+}}}\text{,}\,{{\text{H}}^{\text{+}}}\text{+O}{{\text{H}}^{\text{-}}}\xrightarrow{{}}{{\text{H}}_{\text{2}}}\text{O,}\,\text{Fe(OH}{{\text{)}}_{\text{2}}}\text{,}\,\text{Fe(OH}{{\text{)}}_{\text{3}}}\\\text{F}{{\text{e}}^{\text{3+}}}\text{,}\,{{\text{H}}^{\text{+}}}\text{+CO}_{\text{3}}^{\text{2-}}\xrightarrow{{}}\text{Fe(OH}{{\text{)}}_{\text{3}}}\text{+}{{\text{H}}_{\text{2}}}\text{O+C}{{\text{O}}_{\text{2}}}\\\text{Cu+2F}{{\text{e}}^{\text{3+}}}\xrightarrow{{}}\text{C}{{\text{u}}^{\text{2+}}}\text{+2F}{{\text{e}}^{\text{2+}}}\\\text{3F}{{\text{e}}^{\text{2+}}}\text{+4}{{\text{H}}^{\text{+}}}\text{+NO}_{\text{3}}^{\text{-}}\xrightarrow{{}}\text{3F}{{\text{e}}^{\text{3+}}}\text{+NO+2}{{\text{H}}_{\text{2}}}\text{O}\end{array}$