Chemistry - Electrochemistry Question with Solution | TestHub
Standard electrode potential data are useful for understanding the suitability of an oxidant in a redox titration. Some half cell reactions and their standard potentials are given below:
MnO₄⁻(aq) + 8H⁺(aq) + 5e⁻ → Mn²⁺(aq) + 4H₂O(l);
Cr₂O₇²⁻(aq) + 14H⁺(aq) + 6e⁻ → 2Cr³⁺(aq) + 7H₂O(l);
Fe³⁺(aq) + e⁻ → Fe²⁺(aq);
Cl₂(g) + 2e⁻ → 2Cl⁻(aq);
Identify the correct statements regarding the quantitative estimation of aqueous Fe(NO₃)₂ :
Options:(select one or more)
Answer:
Solution:
In (A) MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
2Cl⁻ → Cl₂ + 2e⁻
MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
Fe²⁺ → Fe³⁺ + e⁻
The above calculations clearly show that MnO₄⁻ can oxidize both HCl and Fe²⁺. Hence, HCl should not be used as a medium for quantitative estimations.
In (B) Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O
2Cl⁻ → Cl₂ + 2e⁻
Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O
Fe²⁺ → Fe³⁺ + e⁻
Since Cr₂O₇²⁻ is not reduced by HCl, HCl can be used as a medium for K₂Cr₂O₇ to oxidize Fe²⁺.
Since in (b), (c), and (d) the acid (medium) is not oxidized, it can be used quantitatively to oxidize Fe²⁺.
