Question

The order of negative standard potential values of \(\text{Li}\), \(\text{Na}\), \(\text{K}\) is

• A. \(\text{Li} > \text{Na} > \text{K}\)
• B. \(\text{K} > \text{Na} > \text{Li}\)
• C. \(\text{Na} > \text{K} > \text{Li}\)
• D. \(\text{Li} > \text{K} > \text{Na}\)

Hint:

Lithium represents an anomaly in group 1; despite having the highest ionization energy, its tiny ionic size creates a massive hydration enthalpy, crowning it as the strongest reducing agent in aqueous solutions across the periodic table.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
We need to arrange the elements Lithium (Li), Sodium (Na), and Potassium (K) based on their "negative standard potential values" (which refers to the magnitude of their standard reduction potentials, i.e., \(-E^\circ\)).
Step 2: Detailed Explanation:
The standard reduction potentials (\(E^\circ\)) for these alkali metal cations are known experimentally as:

• \(E^\circ_{\text{Li}^+/\text{Li}} = -3.05 \text{ V}\)
• \(E^\circ_{\text{K}^+/\text{K}} = -2.93 \text{ V}\)
• \(E^\circ_{\text{Na}^+/\text{Na}} = -2.71 \text{ V}\)

Lithium has the most negative reduction potential in the entire electrochemical series due to its remarkably high hydration enthalpy, which powerfully outweighs its relatively high ionization enthalpy when placed in an aqueous solution. Potassium is more reactive than Sodium, reflecting its lower ionization energy and translating to a more negative reduction potential than Na.
The question asks for the order of their negative standard potential values. Taking the negative of their \(E^\circ\) yields positive magnitudes:

• \(-E^\circ_{\text{Li}} = 3.05 \text{ V}\)
• \(-E^\circ_{\text{K}} = 2.93 \text{ V}\)
• \(-E^\circ_{\text{Na}} = 2.71 \text{ V}\)

Arranging these magnitudes in descending order, we clearly see: \[ 3.05>2.93>2.71 \] This perfectly corresponds to the elemental order: \(\text{Li}>\text{K}>\text{Na}\).
Step 3: Final Answer:
The correct order is \(\text{Li}>\text{K}>\text{Na}\).