Question

`Cu^(+)` ion is not stable in aqueous solution because of disproportionation reaction. `E^(@)` value for disproportionation of `Cu^(+)` is (Given `E_(Cu^(2+)//Cu^(+))^(@)=0.15,E_(Cr^(2+)//Cu)^(@)=0.34V`)
A. `-0.49V`
B. `0.49V`
C. `-0.38V`
D. `0.38V`

Answer 1

Correct Answer - D
The required reaction `(Cu^(++)+Cuto2Cu^(+))` can be obtained by using the following reactions.
`Cu^(++)+e^(-)toCu^(+),E_(Cu^(++)//Cu^(+))^(o)=0.15V` . . .(i)
`Cu^(++)+2e^(-)toCu,E_(Cu^(++)//Cu)^(o)=0.34V` . . (ii)
Multiplying eq. (i) by 2 we get
`2Cu^(++)+2e^(-)to2Cu^(+)` . . . (iii)
`DeltaG_(1)=-nFE=-2xxFxx0.15`
`Cu^(++)+2e^(-)toCu` . . . (iv)
Subtract the eq. (iv) from (iii)
`Cu^(++)+Cuto2Cu^(+)`
`DeltaG_(3)=-nFE=-1xxFxxE^(o)`
Also `DeltaG_(3)=DeltaG_(1)-DeltaG_(2)`
`-1FE^(o)=(-2Fxx0.15)-(-2Fxx0.34)`
`E^(o)=-0.38`
this is the value of the reaction
`Cu^(++)+Cuto2Cu^(+)`
but the given reaction is just reverse of it
`thereforeE_(cell)` for given reaction =+0.38V.