CBSE Class 11-science Answered

H₂S + KMnO₄ + H₂SO₄ → S+ MnSO₄ + KHSO₄ + H₂O Balance by oxidation number method step by step explain please

Asked by govtsecschoolnayaganv051 | 18 Aug, 2018, 17:08: PM

Expert Answer

Step 1

The skeleton equation is:

H₂S + KMnO₄ + H₂SO₄ → S+ MnSO₄ + KHSO₄ + H₂O

Step 2

(a) The oxidation number of various atoms involved in the reaction.

$space subscript plus 1 space minus 2 space space space space space plus 1 space plus 7 space minus 2 space space space space space space space plus 1 space plus 6 space minus 2 space space space space space space space space 0 space space space space space space plus 2 space plus 6 space minus 2 space space space space space space space plus 1 space plus 1 space plus 6 space minus 2 space space space space space space space plus 1 space minus 2 end subscript space space straight H subscript 2 straight S space plus space space space space KMnO subscript 4 space end subscript plus space space space straight H subscript 2 SO subscript 4 space rightwards arrow space straight S space plus space space space space MnSO subscript 4 space plus space space space space space KHSO subscript 4 space space space space space space plus space straight H subscript 2 straight O space$

(b) Identify and write out all the redox couple in reaction.

$bold Oxidation bold colon space space space space space space 2 stack straight H subscript 2 straight S with plus 1 space minus 2 on top space space plus space KMnO subscript 4 space end subscript plus space straight H subscript 2 straight S space rightwards arrow space straight S with 0 on top space space plus space stack KHSO subscript 4 with plus 1 plus 1 plus 6 minus 2 on top space plus space MnSO subscript 4 space plus space 10 space straight e to the power of minus space bold Reduction bold colon space space stack KMnO subscript 4 with plus 1 plus 7 minus 2 on top space plus space 2 space straight H subscript 2 SO subscript 4 space end subscript plus space 5 space straight e to the power of minus space rightwards arrow space stack MnSO subscript 4 with plus 2 space plus 6 minus 2 on top space plus space KHSO subscript 4$

Step 3

Balance the atoms in each half reaction

a) Balance all other atoms except hydrogen an oxygen

$bold Oxidation bold colon space space space space space space 2 stack straight H subscript 2 straight S with plus 1 space minus 2 on top space plus space KMnO subscript 4 space plus space straight H subscript 2 straight S space rightwards arrow space straight S with 0 on top space space plus space stack KHSO subscript 4 with plus 1 plus 1 plus 6 minus 2 on top plus space MnSO subscript 4 space plus space 10 space straight e to the power of minus to the power of blank end exponent bold Reduction bold colon space space stack KMnO subscript 4 with plus 1 plus 7 minus 2 on top space plus 2 straight H subscript 2 SO subscript 4 space plus space 5 space straight e to the power of minus space rightwards arrow space stack MnSO subscript 4 with plus 2 space plus 6 minus 2 on top space plus space KHSO subscript 4$

b) Balance the charge:

$bold Oxidation bold colon space space space space space space 2 stack straight H subscript 2 straight S with plus 1 space minus 2 on top space plus space KMnO subscript 4 space plus space straight H subscript 2 straight S space rightwards arrow space straight S with 0 on top space space plus space stack KHSO subscript 4 with plus 1 plus 1 plus 6 minus 2 on top plus space MnSO subscript 4 space plus space 10 space straight e to the power of minus space plus space 10 straight H to the power of plus bold Reduction bold colon space space stack KMnO subscript 4 with plus 1 plus 7 minus 2 on top space plus 2 straight H subscript 2 SO subscript 4 space plus space 5 space straight e to the power of minus space plus space 5 straight H to the power of plus space rightwards arrow space stack MnSO subscript 4 with plus 2 space plus 6 minus 2 on top space plus space KHSO subscript 4$

c) Balance the oxygen atoms

Step 4: Make electron gain equivalent to electron lost.

$bold Oxidation bold colon space space space space space space 2 stack straight H subscript 2 straight S with plus 1 space minus 2 on top space plus space KMnO subscript 4 space plus space straight H subscript 2 straight S space plus space 4 straight H subscript 2 straight O rightwards arrow space straight S with 0 on top space space plus space stack KHSO subscript 4 with plus 1 plus 1 plus 6 minus 2 on top plus space MnSO subscript 4 space plus space 10 space straight e to the power of minus space plus space 10 straight H to the power of plus space space space space..... space Multiply space by space 1 bold Reduction bold colon space space stack KMnO subscript 4 with plus 1 plus 7 minus 2 on top space plus 2 straight H subscript 2 SO subscript 4 space plus space 5 space straight e to the power of minus space plus space 5 straight H to the power of plus space rightwards arrow space stack MnSO subscript 4 with plus 2 space plus 6 minus 2 on top space plus space KHSO subscript 4 space plus space 4 straight H subscript 2 straight O space space space space space space space space space space space space space space space space space space space space space space space space.......... Multiply space by space 2 We space get comma bold Oxidation bold colon space space space space space space 2 stack straight H subscript 2 straight S with plus 1 space minus 2 on top space plus space KMnO subscript 4 space plus space straight H subscript 2 straight S space plus space 4 straight H subscript 2 straight O rightwards arrow space straight S with 0 on top space space plus space stack KHSO subscript 4 with plus 1 plus 1 plus 6 minus 2 on top plus space MnSO subscript 4 space plus space 10 space straight e to the power of minus space plus space 10 straight H to the power of plus space space bold Reduction bold colon space space stack 2 KMnO subscript 4 with plus 1 plus 7 minus 2 on top space plus 4 space straight H subscript 2 SO subscript 4 space plus space 10 space straight e to the power of minus space plus 10 space straight H to the power of plus space rightwards arrow space stack 2 space MnSO subscript 4 with plus 2 space plus 6 minus 2 on top space plus 2 space KHSO subscript 4 space plus space 8 space straight H subscript 2 straight O$

Step 5: Add the half-reactions together.

$space space 2 stack straight H subscript 2 straight S with plus 1 space minus 2 on top space plus space stack 3 space KMnO subscript 4 with plus 1 plus 7 minus 2 on top space plus 4 space straight H subscript 2 SO subscript 4 plus straight H subscript 2 straight S space plus 10 space straight e to the power of minus space plus 10 space straight H to the power of plus space rightwards arrow space straight S with 0 on top space plus space space stack 3 space MnSO subscript 4 space with plus 2 space plus 6 minus 2 on top plus space 3 space KHSO subscript 4 space plus space 8 space straight H subscript 2 straight O space plus space 10 space straight e to the power of minus space plus space 10 straight H to the power of plus space space$

Step 6 : Simplify the equation:

$space space 3 stack straight H subscript 2 straight S with plus 1 space minus 2 on top space plus space stack 3 space KMnO subscript 4 with plus 1 plus 7 minus 2 on top space plus 4 space straight H subscript 2 SO subscript 4 space rightwards arrow space straight S with 0 on top space plus space space stack 3 space MnSO subscript 4 space with plus 2 space plus 6 minus 2 on top plus space 3 space KHSO subscript 4 space plus space 4 space straight H subscript 2 straight O space$