Question

The standard reduction potential for $\rightarrow$ and $\rightarrow$ electrodes are $NH_{4}Cl + MgCl_{2}$ and $NH_{4}OH +$ volt respectively. For the given cell reaction

$MnO_{2} + C + NH_{4}Cl$, the standard EMF is.

• A.
  • 0.30 V
• B. – 0.58 V
• C.
  • 0.58 V
• D. – 0.30 V

Answer 1

Answer: (D)

– 0.30 V

Answer 2

For the cell reaction, Fe acts as cathode and Sn as anode. Hence,

$E_{cell}^{o} = E_{\text{cathode}}^{o} - E_{\text{anode}}^{o}$= – 0.44 – (– 0.14)= – 0.30V

The negative EMF suggests that the reaction goes

spontaneously in reversed direction.