Electrochemistry

What you'll learn

A friendly, NCERT-aligned walkthrough of Class 12 Electrochemistry: how galvanic cells turn reactions into electricity, standard electrode potentials and the SHE, calculating cell EMF, the Nernst equation with a worked numerical, conductance of solutions, and electrolysis with Faraday's laws.

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Electrochemistry — solved practice questions

8 Class 12 Chemistry questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   In a galvanic (voltaic) cell, oxidation takes place at the:

   • ACathode, which is the positive electrode
   • BAnode, which is the negative electrode
   • CCathode, which is the negative electrode
   • DSalt bridge
   Show answer & solution

   Correct answer: (B) Anode, which is the negative electrode

   In a galvanic cell, oxidation occurs at the anode, which is the negative electrode, while reduction occurs at the positive cathode.

2. Q2easy

   The standard hydrogen electrode (SHE) is assigned a standard electrode potential of:

   • A+1.00 V
   • B-1.00 V
   • C0.00 V
   • D+0.76 V
   Show answer & solution

   Correct answer: (C) 0.00 V

   By convention, the standard hydrogen electrode is the reference electrode and is assigned a standard potential of exactly 0.00 V at all temperatures.

3. Q3medium

   The SI unit of molar conductivity when concentration is expressed in mol m^-3 is:

   • AS cm^2 mol^-1
   • BS m^-1
   • Cohm cm
   • DS m^2 mol^-1
   Show answer & solution

   Correct answer: (D) S m^2 mol^-1

   Molar conductivity = conductivity / concentration. With conductivity in S m^-1 and concentration in mol m^-3, the SI unit is S m^2 mol^-1.

4. Q4medium

   For the cell reaction to be spontaneous under standard conditions, the standard cell potential (E0 cell) and standard Gibbs energy (Delta G0) must satisfy:

   • AE0 cell > 0 and Delta G0 > 0
   • BE0 cell > 0 and Delta G0 < 0
   • CE0 cell < 0 and Delta G0 < 0
   • DE0 cell = 0 and Delta G0 > 0
   Show answer & solution

   Correct answer: (B) E0 cell > 0 and Delta G0 < 0

   Delta G0 = -nFE0 cell. A spontaneous reaction requires Delta G0 < 0, which means E0 cell must be positive.

5. Q5medium

   According to the Nernst equation at 298 K, the potential of an electrode M(n+) + n e- -> M is given by E = E0 - (0.0591/n) log(1/[M^n+]). If [M^n+] increases, the electrode potential:

   • ADecreases
   • BIncreases
   • CRemains unchanged
   • DBecomes zero
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   Correct answer: (B) Increases

   As [M^n+] increases, log(1/[M^n+]) becomes more negative, so the subtracted term decreases, making E larger. A higher ion concentration favours reduction, raising the electrode potential.

6. Q6medium

   How many faradays of charge are required to deposit 1 mole of aluminium from molten Al2O3 (Al^3+ + 3e- -> Al)?

   • A1 F
   • B2 F
   • C3 F
   • D0.5 F
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   Correct answer: (C) 3 F

   Each Al^3+ ion needs 3 electrons, so depositing 1 mole of Al requires 3 moles of electrons, i.e. 3 faradays of charge.

7. Q7hard

   The conductivity of an electrolytic solution generally _____ with dilution, while the molar conductivity _____ with dilution.

   • Adecreases; increases
   • Bincreases; decreases
   • Cincreases; increases
   • Ddecreases; decreases
   Show answer & solution

   Correct answer: (A) decreases; increases

   On dilution, the number of ions per unit volume falls, so conductivity decreases. Molar conductivity increases because it accounts for all ions from a fixed amount of electrolyte, which become more mobile/dissociated.

8. Q8medium

   Kohlrausch's law of independent migration of ions is especially useful for calculating the limiting molar conductivity of:

   • AStrong electrolytes only
   • BNon-electrolytes
   • CMolten salts
   • DWeak electrolytes, which cannot be obtained by extrapolation
   Show answer & solution

   Correct answer: (D) Weak electrolytes, which cannot be obtained by extrapolation

   For weak electrolytes, molar conductivity does not reach a limiting value by simple extrapolation. Kohlrausch's law lets us calculate it by adding the limiting ionic conductivities of the constituent ions.

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