Electrochemistry — Class 12 MCQs with Answers

Electrochemistry — important questions & MCQs with answers (Class 12 Chemistry)

14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 84 are timed and scored when you sign in.

1. Q1Easy

   In a galvanic cell, oxidation occurs at the:

   A.Cathode

   B.Electrolyte

   C.Salt bridge

   D.Anode✓ Correct

   Answer: D. Anode

   Explanation: The anode is where oxidation happens — electrons are lost there, e.g. Zn(s) → Zn²⁺(aq) + 2e⁻ — while the cathode is where reduction occurs; mixing the two up is the classic slip.

2. Q2Easy

   The SI unit of molar conductivity is:

   A.S cm⁻¹

   B.S m⁻¹

   C.S m² mol⁻¹✓ Correct

   D.Ω m

   Answer: C. S m² mol⁻¹

   Explanation: Molar conductivity Λm = κ/c, and dividing S m⁻¹ by mol m⁻³ leaves S m² mol⁻¹ — don't confuse it with κ's own unit, S m⁻¹, the tempting distractor here.

3. Q3Easy

   The Nernst equation at 298 K for a cell reaction (n electrons) is Ecell = E°cell − (0.0591/n) log Q. The factor 0.0591 comes from:

   A.RT/F at 298 K with ln to log conversion✓ Correct

   B.F/RT at 273 K

   C.Avogadro number

   D.Specific heat of water

   Answer: A. RT/F at 298 K with ln to log conversion

   Explanation: 0.0591 = 2.303RT/F at T = 298 K: multiplying RT/F (≈0.0257 V) by 2.303 converts the Nernst equation's natural log into a base-10 log, giving the familiar 0.059 V figure.

4. Q4Easy

   In a galvanic cell, the anode is the:

   A.Positive electrode

   B.Negative electrode✓ Correct

   C.Neutral electrode

   D.Cathode

   Answer: B. Negative electrode

   Explanation: In a galvanic cell the anode releases electrons into the external circuit, making it the negative terminal — the reverse of an electrolytic cell, where the anode is positive.

5. Q5Easy

   The SI unit of specific conductivity (κ) is:

   A.S m⁻¹✓ Correct

   B.Ω m

   C.S m²

   D.Ω⁻¹

   Answer: A. S m⁻¹

   Explanation: Specific conductivity κ has SI unit S m⁻¹, the reciprocal of resistivity (Ω m) — don't confuse it with molar conductivity Λm, whose unit carries an extra mol⁻¹.

6. Q6Easy

   At equilibrium, the cell EMF (Ecell) is:

   A.Equal to E°cell

   B.Maximum

   C.Zero✓ Correct

   D.Infinite

   Answer: C. Zero

   Explanation: At equilibrium the cell has stopped doing net work — Q equals K and the log term cancels, so Ecell falls to zero even though E°cell itself stays fixed at its non-zero value.

7. Q7Medium

   Standard emf of a cell is given by:

   A.E°_cathode − E°_anode✓ Correct

   B.E°_cathode + E°_anode

   C.E°_anode − E°_cathode

   D.E°_cathode × E°_anode

   Answer: A. E°_cathode − E°_anode

   Explanation: E°cell = E°cathode − E°anode, with both values taken as standard reduction potentials — subtracting the other way round silently flips the sign of every calculation that follows.

8. Q8Medium

   Kohlrausch's law of independent migration of ions allows calculation of:

   A.Boiling point

   B.Λ°_m of weak electrolytes✓ Correct

   C.Vapour pressure

   D.pH

   Answer: B. Λ°_m of weak electrolytes

   Explanation: Kohlrausch's law gives Λ°m as the sum of ionic contributions, so it lets you calculate the limiting molar conductivity of a weak electrolyte like CH₃COOH, which can't be measured directly by extrapolation.

9. Q9Medium

   The Nernst equation at 298 K for a cell reaction is:

   A.E = E° × log Q

   B.E = E° + (0.059/n) log Q

   C.E = E° − (n/0.059) log Q

   D.E = E° − (0.059/n) log Q✓ Correct

   Answer: D. E = E° − (0.059/n) log Q

   Explanation: The Nernst equation is E = E° − (0.059/n) log Q at 298 K, derived from E = E° − (RT/nF) ln Q; note the minus sign and that n sits in the denominator, not multiplying log Q.

10. Q10Medium

    Given E°(Ag⁺/Ag) = +0.80 V and E°(Cu²⁺/Cu) = +0.34 V. The E°cell for Cu|Cu²⁺||Ag⁺|Ag is:

    A.−0.46 V

    B.+1.14 V

    C.+0.46 V✓ Correct

    D.+0.80 V

    Answer: C. +0.46 V

    Explanation: E°cell = E°cathode − E°anode = 0.80 − 0.34 = +0.46 V for Cu|Cu²⁺||Ag⁺|Ag, since Ag⁺/Ag (cathode) is reduced and Cu is oxidised at the anode — reversing the subtraction gives the wrong-signed −0.46 V.

11. Q11Medium

    The molar conductivity of 0.05 M solution of a salt is 100 S cm² mol⁻¹. Its specific conductivity (κ) is:

    A.5 × 10⁻³ S cm⁻¹✓ Correct

    B.5 × 10⁻² S cm⁻¹

    C.2 × 10⁻³ S cm⁻¹

    D.500 S cm⁻¹

    Answer: A. 5 × 10⁻³ S cm⁻¹

    Explanation: κ = Λm × c / 1000 = 100 × 0.05 / 1000 = 5 × 10⁻³ S cm⁻¹ — the 1000 factor converts the concentration from mol L⁻¹ to mol cm⁻³ inside this relation.

12. Q12Hard

    How many faradays are required to deposit 1 mol of Al from molten Al₂O₃?

    A.1

    B.2

    C.6

    D.3✓ Correct

    Answer: D. 3

    Explanation: Al³⁺ + 3e⁻ → Al needs 3 mol of electrons per mole of Al deposited, so depositing 1 mol Al takes 3 faradays — don't default to the 2 F that many divalent-ion problems use.

13. Q13Hard

    Conductivity of saturated AgCl solution at 298 K is 1.382 × 10⁻⁶ S cm⁻¹ (water κ negligible). Given Λ°m(AgCl) = 138.2 S cm² mol⁻¹, the solubility (mol L⁻¹) of AgCl is:

    A.1.0 × 10⁻⁶

    B.1.0 × 10⁻⁴

    C.1.0 × 10⁻⁵✓ Correct

    D.1.0 × 10⁻³

    Answer: C. 1.0 × 10⁻⁵

    Explanation: c = 1000κ/Λ°m = 1000 × 1.382 × 10⁻⁶ / 138.2 = 1.0 × 10⁻⁵ mol L⁻¹ — for a sparingly soluble salt like AgCl this dissolved-ion concentration equals the molar solubility directly, since it fully dissociates.

14. Q14Hard

    For Mg|Mg²⁺(0.001 M)||Cu²⁺(0.0001 M)|Cu, E°cell = 2.71 V at 298 K. Ecell is:

    A.2.6805 V✓ Correct

    B.2.7396 V

    C.2.7100 V

    D.2.7691 V

    Answer: A. 2.6805 V

    Explanation: Ecell = 2.71 − (0.0591/2) log(0.001/0.0001) = 2.71 − 0.02955 × log(10) = 2.71 − 0.02955 = 2.6805 V, since Mg²⁺ (anode) is 10× more concentrated than Cu²⁺ (cathode) here.

Electrochemistry — FAQs

More Class 12 Chemistry chapters

• 01Solutions
• 03Chemical Kinetics
• 04The d- and f-Block Elements
• 05Coordination Compounds
• 06Haloalkanes and Haloarenes
• 07Alcohols, Phenols and Ethers

Class 12 — other subjects

• Class 12 Biology chapters
• Class 12 Computer Science chapters
• Class 12 English chapters
• Class 12 Mathematics chapters
• Class 12 Physics chapters