Question

Which of the following 3d transition metal has the positive standard electrode potential (\(E^\circ\))?

• A. Ni
• B. Cu
• C. V
• D. Mn

Hint:

The reactivity series helps here: Metals below Hydrogen in the activity series have positive reduction potentials. Copper is the only metal from the 3d series commonly found below Hydrogen.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Standard electrode potential (\(E^\circ\)) of a metal measures its tendency to be reduced. For most 3d transition metals, \(E^\circ(M^{2+}/M)\) values are negative because they are more reactive than hydrogen.

Step 2: Detailed Explanation:
1. The standard electrode potential is determined by three factors: enthalpy of atomization, ionization enthalpy, and hydration enthalpy.
2. For most transition metals, the high negative hydration enthalpy compensates for the energy required to atomize and ionize the metal.
3. Copper (Cu): It has an uniquely positive \(E^\circ(Cu^{2+}/Cu) = +0.34 \text{ V}\). This is because the high sum of its first and second ionization enthalpies is not balanced by its hydration enthalpy.
4. Consequently, Copper does not displace hydrogen gas from dilute acids.

Step 3: Final Answer:
Copper (Cu) is the 3d transition metal with a positive standard electrode potential.