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The standard reduction potentials for Zn...

The standard reduction potentials for `Zn^(2+)//Zn, Ni^(2+)//Ni, and Fe^(2+)//Fe` are -0.76, -0.23 and -0.44 V respectively. The reaction `X + y^(2+) rarr + Y` will be spontaneous when :

A

`x=Zn,y=Ni`

B

`x=Ni,y=Fe`

C

`x=Mn,y=Zn`

D

`x=Fe,y=Zn`.

Text Solution

Verified by Experts

The correct Answer is:
A
The reaction `x+y^(2+)rarrx^(2+)+y` will be spontaneous if `E_("cell")^(@)` is +ve
(A) `Zn+Ni^(2+)rarrZn^(2+)+Ni`
`E_("cell")^(@)=E_(cu^(2+)//Ni)^(@)=E_(Zn^(+2)//Zn)^(@)`
`=-0.23-(-0.76)V=0.53V`
(B) `Ni+Fe^(2+)rarrNi^(2+)+Fe`
`E_("cell")^(@)=E_(Fe^(2+)..Fe)^(@)-E_(Ni^(2+)//Ni)^(@)=-0.44-(-.23)V`
=-0.21V
(C) `Ni+Zn^(2+)rarrNi^(2+)+Zn`
`E_("cell")^(@)+Zn ^(2+)rarrNi^(2+)+Zn`
`E_("cell")^(@)=0.53V` from (A)
(D) `Fe+Zn^(2+)rarrFe^(2+)+Zn`
`E_("cell")^(@)=E_(Zn^(2+)//Zn)^(@)-E_(Fe^(2+)//Fe)^(@)`
`=-0.76-(-0.44)=-0.32V`
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