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The standard redox potentials for the re...

The standard redox potentials for the reactions,
`MN^(2+) + 2e^(-)to Mn and Mn^(3+) + e^(-) are `-1.18V and 1.51V respectively. What is the redox potential for the reaction `Mn^(3+)+ 3e^(-) to Mn`?

A

0.33 V

B

1.69 V

C

`– 0.28` V

D

`- 0.85 V`

Text Solution

Verified by Experts

The correct Answer is:
C
`Mn^(2+)+ 2e^(-) rarr Mn` ...(i)
`Delta G^(@)= -nFE^(@)= 2.36F`
`Mn^(3+) + e^(-) rarr Mn^(2+)` ...(ii)
`Delta G^(@)= -nFE^(@)= -1.51F`
Add eqns. (i) and (ii),
`Mn^(3+) + 3e^(-) rarr Mn`
`Delta G^(@)= 2.36F + (-1.5F) = 0.85F`
`Delta G^(@) = -nFE^(@)`
`0.85F= -3 xx F xx E^(@) rArr E^(@)= -0.28V`
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