H2S + KMnO4 + H2SO4 → S+ MnSO4 + KHSO4 + H2
Balance by oxidation number method step by step explain please

Asked by govtsecschoolnayaganv051 | 18th Aug, 2018, 05:08: PM

Expert Answer:

Step 1

The skeleton equation is:

H2S + KMnO4 + H2SO4 → S+ MnSO4 + KHSO4 + H2

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

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

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

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

Answered by Ramandeep | 23rd Aug, 2018, 10:19: AM