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OJEE Electrochemistry — practice questions — page 3

Explore 111 free Electrochemistry questions in OJEE Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Electrochemistry questions and exercises with answers

Showing questions 61–90 of 111.

Why is the cell potential temperature-dependent?Read the answer and worked solution →For Hg²⁺/Hg (E° = +0.79 V) and Cu²⁺/Cu (E° = +0.34 V), the spontaneous reaction is:Read the answer and worked solution →Conductivity of a 0.01 M NaCl solution is 0.0014 S/cm. Molar conductivity Λ_m:Read the answer and worked solution →Lead-acid battery during DISCHARGE: PbO2 + Pb + 2H2SO4 → 2PbSO4 + 2H2O. The role of PbO2 is:Read the answer and worked solution →Corrosion of iron involves which type of reaction?Read the answer and worked solution →In electroplating silver onto a spoon, the cathode is:Read the answer and worked solution →Electrochemistry deals with:Read the answer and worked solution →In a galvanic (voltaic) cell, oxidation occurs at:Read the answer and worked solution →Standard electrode potential of standard hydrogen electrode (SHE) is:Read the answer and worked solution →In Daniell cell (Zn | Zn²⁺ || Cu²⁺ | Cu), electron flow in external circuit:Read the answer and worked solution →Faraday's first law of electrolysis: amount of substance liberated at electrode is proportional to:Read the answer and worked solution →Conductance is the:Read the answer and worked solution →Nernst equation for cell potential (at 25°C):Read the answer and worked solution →For Daniell cell, cell reaction Zn + Cu²⁺ → Zn²⁺ + Cu. Cell EMF:Read the answer and worked solution →Faraday constant F is:Read the answer and worked solution →Standard Gibbs free energy and cell EMF relation:Read the answer and worked solution →Relation between equilibrium constant K and E°:Read the answer and worked solution →How many coulombs are needed to deposit 1 mole of Cu from CuSO₄ (Cu²⁺ + 2e⁻ → Cu)?Read the answer and worked solution →Time to deposit 1.27 g of Cu from CuSO₄ solution at 2 A current (Cu atomic mass = 63.5):Read the answer and worked solution →Equilibrium constant for cell with E° = 0.118 V, n = 2, at 25°C:Read the answer and worked solution →Specific conductance κ has units:Read the answer and worked solution →Hydrogen-Oxygen fuel cell produces:Read the answer and worked solution →Lead acid battery (used in cars) overall reaction:Read the answer and worked solution →Standard reduction potential ranking. Which is the strongest oxidizing agent?Read the answer and worked solution →Resistance of a conductivity cell filled with 0.1 M KCl is 100 Ω. Specific conductivity κ of solution (cell constant = 1.5 cm⁻¹):Read the answer and worked solution →For a cell reaction reversed in direction, E° becomes:Read the answer and worked solution →Galvanic cell or electrolytic cell?Read the answer and worked solution →Complete the standard cell potential relationRead the answer and worked solution →Order these electrodes by standard potential, lowest firstRead the answer and worked solution →Match each electrode to the potential your syllabus givesRead the answer and worked solution →

Worked practice questions

Why is the cell potential temperature-dependent?

  1. Both ΔG and the Nernst RT/nF term are T-dependent
  2. E does not depend on T
  3. Only for non-redox cells
  4. Only when K = 1
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Correct answer: A. Both ΔG and the Nernst RT/nF term are T-dependent

E° = -ΔG°/(nF), and ΔG° = ΔH° - TΔS°. So E° varies with T according to ΔS°. Also Nernst correction term has RT/F. Hence cells have specific 'standard temperature' (typically 25°C).

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For Hg²⁺/Hg (E° = +0.79 V) and Cu²⁺/Cu (E° = +0.34 V), the spontaneous reaction is:

  1. Hg + Cu²⁺ → Hg²⁺ + Cu
  2. Neither
  3. Both
  4. Cu + Hg²⁺ → Cu²⁺ + Hg
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Correct answer: D. Cu + Hg²⁺ → Cu²⁺ + Hg

Larger E° is the stronger oxidizer at the cathode. Hg²⁺ (E° = +0.79) > Cu²⁺ (+0.34), so Hg²⁺ is the oxidizer. Cu (lower E°) gets oxidized. **Net:** Cu + Hg²⁺ → Cu²⁺ + Hg. E°_cell = 0.79 - 0.34 = +0.45 V (positive, spontaneous).

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Conductivity of a 0.01 M NaCl solution is 0.0014 S/cm. Molar conductivity Λ_m:

  1. 140 S·cm²/mol
  2. 14 S·cm²/mol
  3. 1400 S·cm²/mol
  4. 1.4 S·cm²/mol
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Correct answer: A. 140 S·cm²/mol

Λ_m = κ × 1000 / c (with c in mol/L). = 0.0014 × 1000 / 0.01 = 140 S·cm²/mol. (Or in SI: κ/c with appropriate unit conversion.)

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