K₂Cr₂O7+6Fe₃O4+31H₂SO4=K₂SO₄+Cr₂(SO₄)₃+9Fe₂(SO₄)₃+31H₂O1K₂Cr₂O7+xFe₃O4+yH₂SO4=1K₂SO₄+1Cr₂(SO₄)₃+(3x/2)Fe₂(SO₄)₃+yH₂OSO₄²-守恒:y=1+3+(3x/2)×3O守恒:7+4x=y解方程组得x=6, y=31,K₂Cr₂O7+6Fe₃O4+31H₂SO4=K₂SO₄+Cr₂(SO₄)₃+9Fe₂(SO₄)₃+31H₂O