Question

In the given electrochemical cell, $Ag(s) | AgCl(s) | FeCl₂(aq), FeCl₃(aq) | Pt(s)$ at 298 K, the cell potential (E___cell) will increase when:
A. Concentration of Fe²⁺ is increased.
B. Concentration of Fe³⁺ is decreased.
C. Concentration of Fe²⁺ is decreased.
D. Concentration of Fe³⁺ is increased.
E. Concentration of Cl⁻ is increased.
Choose the correct answer from the options given below :

• A. A and E Only
• B. B Only
• C. C, D and E Only
• D. A and B Only

Hint:

Think of the Nernst Equation like Le Chatelier's Principle: to push the voltage higher, you need more reactants or fewer products.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The Nernst Equation relates cell potential to the concentrations of reactants and products. To increase \(E_{cell}\), we must decrease the reaction quotient \(Q\).
Step 2: Key Formula or Approach:
1. Anode reaction: \(Ag(s) + Cl^-(aq) \rightarrow AgCl(s) + e^-\).
2. Cathode reaction: \(Fe^{3+}(aq) + e^- \rightarrow Fe^{2+}(aq)\).
3. Net Reaction: \(Ag(s) + Cl^-(aq) + Fe^{3+}(aq) \rightarrow AgCl(s) + Fe^{2+}(aq)\).
4. Nernst Equation: \(E_{cell} = E^\circ_{cell} - \frac{0.059}{1} \log \frac{[Fe^{2+}]}{[Cl^-][Fe^{3+}]}\).
Step 3: Detailed Explanation:
From the expression \(Q = \frac{[Fe^{2+}]}{[Cl^-][Fe^{3+}]}\), to increase \(E_{cell}\), \(Q\) must decrease.
- Decreasing \([Fe^{2+}]\) will decrease \(Q\) (Statement C).
- Increasing \([Fe^{3+}]\) will decrease \(Q\) (Statement D).
- Increasing \([Cl^-]\) will decrease \(Q\) (Statement E).
Step 4: Final Answer:
The correct options are C, D, and E Only.