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Question #44079

Difficulty: 8/10 | 🟢 Free

The Question

A localized corrosion cell forms on a structural iron beam exposed to an aerated aqueous solution of 0.1 M AlCl30.1\text{ M } AlCl_3 at 298 K298\text{ K}. The anodic process involves the oxidation of Fe(s)Fe(s) to Fe2+(aq)Fe^{2+}(aq), while the cathodic process is the reduction of O2(g)O_2(g) to OH−(aq)OH^-(aq). Given the standard reduction potentials: EFe2+/Fe∘=−0.44 VE^\circ_{Fe^{2+}/Fe} = -0.44\text{ V} and EO2/OH−∘=+0.40 VE^\circ_{O_2/OH^-} = +0.40\text{ V}. The first hydrolysis constant (KhK_h) of [Al(H2O)6]3+[Al(H_2O)_6]^{3+} is 1.0×10−51.0 \times 10^{-5}. Assume the partial pressure of O2(g)O_2(g) is 1 bar1\text{ bar}, the local concentration of Fe2+Fe^{2+} is 1.0×10−2 M1.0 \times 10^{-2}\text{ M}, and Kw=1.0×10−14K_w = 1.0 \times 10^{-14}. Calculate the operating cell potential (EcellE_{cell}) of this corrosion cell. (Take 2.303RTF=0.06 V\frac{2.303 RT}{F} = 0.06\text{ V} at 298 K298\text{ K}).

Options

  • A.

    1.56 V

  • B.

    1.32 V

  • C.

    1.08 V

  • D.

    1.44 V

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

Ionic Product of Water (Kw)|Nernstian Redox Equilibrium|Stock Notation Logic|Corrosion as Electrochemical Process

Why This Question Is Tricky

Common Mistakes

This problem tests the integration of ionic equilibrium (salt hydrolysis) with Nernstian redox thermodynamics.

Students frequently fall into the trap of assuming standard conditions ([OH−]=1 M[OH^-] = 1\text{ M}) or neutral water (pH = 7) for corrosion cells.

The hidden variable is the local [OH−][OH^-] concentration, which is drastically suppressed by the acidic hydrolysis of the Al3+Al^{3+} ions.

Failing to couple KwK_w and KhK_h to the cathodic half-reaction leads to a massive stoichiometric error in the Nernst equation due to the 4th power dependence on [OH−][OH^-].

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterEquilibrium - Class 11 Part 1
ConceptIonic Product of Water (Kw)
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree