Question

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 $X + Y^{2+} \to X^{2+} + Y$ will be spontaneous when :

• A. $X = Ni, Y = Fe$
• B. $X = Ni, Y = Zn$
• C. $X= Fe, Y = Zn$
• D. $X= Zn, Y = Ni$

Answer 1

Answer: (D)

$X + Y^{2+} \to X^{2+} + Y$
For reaction to be spontaneous $Eº^{\circ}$ must be positive.
$E^{\circ}_{Zn / Zn^{+2}} + E^{\circ}_{Ni^{2+} / Ni }= 0.76 + \left(- 0.23\right) = + 0.53$ (positive)