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Question #44895

Difficulty: 8/10 | 🟢 Free

The Question

A 50.0 mL aqueous solution contains $0.02$ M $\ce{U(C2O4)2}$ and $0.03$ M $\ce{FeC2O4}$ dissolved in dilute $\ce{H2SO4}$ . This solution is titrated with $0.05$ M $\ce{KMnO4}$ .

At 298 K, a rapid titration captures only the instantaneous outer-sphere electron transfer reactions, requiring $V_1$ mL of $\ce{KMnO4}$ to reach the first persistent pale pink endpoint.

At 350 K, a prolonged titration ensures complete thermodynamic oxidation of all oxidizable species, requiring $V_2$ mL of $\ce{KMnO4}$ .

Given that the oxidations of $\ce{U^{4+}}$ to $\ce{UO2^{2+}}$ and $\ce{C2O4^{2-}}$ to $\ce{CO2}$ involve inner-sphere mechanisms and bond cleavages that are kinetically frozen during the rapid 298 K titration, calculate the value of $(V_2 - V_1)$ .

Options

A.
36.0 mL
B.
28.0 mL
C.
20.0 mL
D.
8.0 mL

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Actinoid Oxidation State Variety|KMnO₄ Redox pH Dependency|Variable Oxidation State Stability

Why This Question Is Tricky

Common Mistakes

This problem tests the critical distinction between thermodynamic feasibility and kinetic viability in redox titrations.

Students often blindly apply the n-factor to all oxidizable species present, ignoring mechanistic barriers.

The formation of the actinyl ion ( $\ce{UO2^{2+}}$ ) requires the creation of strong U=O bonds (inner-sphere oxygen transfer), which has a high activation energy and is kinetically sluggish at room temperature.

Similarly, oxalate oxidation requires C-C bond cleavage.

By explicitly stating the kinetic freeze, the problem forces the student to selectively apply stoichiometry based on the reaction mechanism at different temperatures, while also avoiding the stoichiometric trap of missing the oxalate ions contributed by the uranium salt.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	D and F Block Elements - Class 12
Concept	Actinoid Oxidation State Variety
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free