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Question #44126

Difficulty: 8/10 | 🟢 Free

The Question

An electrochemical cell contains 1.0 L1.0\text{ L} of an aqueous solution comprising 2.0 M \ceNaCl2.0\text{ M } \ce{NaCl} and 0.1 M \ceNa2SO40.1\text{ M } \ce{Na2SO4} at 298 K298\text{ K}. Electrolysis is performed using inert platinum electrodes by passing a constant current of 9.65 A9.65\text{ A} for 10,000 s10,000\text{ s}. The primary gas evolved at the anode is collected and completely reacted with an excess of hot, concentrated \ceNaOH(aq)\ce{NaOH}(aq).

Assuming 100%100\% current efficiency for the kinetically favored anodic process, identify the major chlorine-containing oxyanion formed in the final solution and calculate its amount.

(Given: 1 F=96500 C mol−11\text{ F} = 96500\text{ C mol}^{-1}; Standard oxidation potentials: E\ceCl−/\ceCl2∘=−1.36 VE^\circ_{\ce{Cl-}/\ce{Cl2}} = -1.36\text{ V}, E\ceH2O/\ceO2∘=−1.23 VE^\circ_{\ce{H2O}/\ce{O2}} = -1.23\text{ V}, E\ceSO42−/\ceS2O82−∘=−2.01 VE^\circ_{\ce{SO4^{2-}}/\ce{S2O8^{2-}}} = -2.01\text{ V})

Options

  • A.

    \ceClO3−,0.167 mol\ce{ClO3-}, 0.167 \text{ mol}

  • B.

    \ceClO−,0.500 mol\ce{ClO-}, 0.500 \text{ mol}

  • C.

    \ceClO3−,0.500 mol\ce{ClO3-}, 0.500 \text{ mol}

  • D.

    \ceClO3−,0 mol\ce{ClO3-}, 0 \text{ mol}

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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

Oxidation State Extremes|Electrolysis Product Prediction

Why This Question Is Tricky

Common Mistakes

This question tests the critical distinction between thermodynamic and kinetic control in electrochemistry, specifically the 'Overpotential Effect'.

Students often rely solely on Standard Oxidation Potentials, incorrectly predicting that water will oxidize to oxygen gas because its oxidation potential is less negative than that of chloride.

However, the kinetic barrier (overpotential) for oxygen evolution on platinum electrodes is exceptionally high, making chlorine evolution the favored pathway in concentrated brine.

Additionally, it traps students who confuse the disproportionation products of halogens in alkali; cold/dilute sodium hydroxide yields hypochlorite (oxidation state +1), whereas the specified hot/concentrated conditions yield chlorate (oxidation state +5), testing knowledge of oxidation state extremes and reaction stoichiometry.

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Question Information

SubjectChemistry
ChapterRedox Reactions - Class 11 Part 2
ConceptOxidation State Extremes
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree