Chemistry - Electrochemistry Question with Solution | TestHub

Question Explanation: Determine non-true facts about standard potential.

Concept: Electrochemical Series and Cell Conventions.

Solution:

1. If $E_{M^{n+}/M}^{\circ }$ is negative (i.e., $<0$), M is a stronger reducing agent than H₂. The spontaneous reaction will be the oxidation of M and the reduction of H⁺ :$M^{}+n{H}^{+}\to M^{n+}+\frac{n}{2}{H}_2$ H⁺ is reduced to H₂ by M . (True)

2. If $E_{M^{a+}/M}^{\circ }$ is positive (i.e., $>0$ V), Mⁿ⁺ is a stronger oxidizing agent than H⁺. The reverse reaction is spontaneous: the oxidation of H₂ and the reduction of Mⁿ⁺ :

$M^{n+}+\frac{n}{2}{H}_2\to M+n{H}^{+}$. $M^{n+}$ is reduced to M by H₂. (True)

3. M will act as the negative electrode to produce a spontaneous cell reaction. This is only true when M is more active than H₂ (i.e., $E^{\circ }<0$). Without specifying E⁰, the statement is not universally true for all $M_{}$. (Not True)

4. Active metals (like Zn, Na, Mg) have negative $E_{}^{\circ }$ (less easily reduced), and their ions are weak oxidants, making them not easily reducible by H₂ (a weak reductant). Noble metals (like Cu, Ag, Au) have positive $E_{}^{\circ }$ and their ions are strong oxidants, making them easily reducible by H₂. The statement incorrectly reverses the reducibility of active and noble metal compounds by H₂. (Not True)

Final Answer: The correct options are (C) and (D).