Question

The standard electrode potentials of $Zn$ and $Ni$ respectively are $-0.76$ V and $-0.25$ V. Then the standard emf of the spontaneous cell by coupling these under standard conditions is:

• A. + 1.01 V
• B. - 0.51 V
• C. + 0.82 V
• D. + 0.25 V
• E. + 0.51 V

Answer 1

The correct option is E + 0.51 V

The standard electrode potential of $Zn\left(E_{anode}^o\right)=-0.76V$

The standard electrode potential of $Ni\left(E_{cathode}^o\right)=-0.25$

For spontaneous reaction $E_{cell}$ should be positive.

So, the reaction should be:

$Zn\left(s\right)+N{i}^{2+}\left(aq\right)⟶Z{n}^{2+}\left(aq\right)+Ni\left(s\right)$

$E_{cell}^o=E_{\left(cathode\right)}^o-E_{\left(anode\right)}^o$

$=-0.25-(-0.76)=+0.51V$