Answer to Question #206046 in General Chemistry for Fiona Yvonne Balia

Question

Balance the following redox reactions by the oxidation state change method.

K₂Cr₂O₇+FeSO₄+H₂SO₄→K₂SO₄+Cr₂(SO₄)₃+Fe₂(SO₄)+H₂O

Answer 1

Writing oxidation numbers of all the atoms.

K₂= +2

​Cr₂ = +6

​O₇ = -2

​​Fe = +2

S = +6

O₄ = -2

​H2 = +1

​S = +6

O₄ = -2

​Cr_{2 = +3}

​S = +6

Change in Oxidation number has occurred in chromium and iron.

K₂Cr₂O₇ (+6)→Cr₂ (SO4) (+3)

FeSO₄ (+2) --> Fe₂(SO4) (+3)

Decrease in Ox. no. of Cr per molecule =(2×6−2×3)=6 units

Increase in Ox. no. of Fe per molecule =1 unit

Hence, eq. (ii) should be multiplied by 6

K₂Cr₂O₇ + 6FeSO₄→Cr2(SO₄)3​+3Fe₂(SO₄)3

To balance hydrogen and oxygen, 7H2

​O should be added on RHS. Hence, balanced equation is,

K₂Cr₂O₇​+6FeSO₄​+7H₂​SO₄ --> Cr₂​(SO₄​)3

​+3Fe₂​(SO₄))3​ +K₂SO₄​+7H₂O.