Electrochemistry is a high-scoring chapter because it directly connects thermodynamics (, , ) with measurable voltages (), and also explains practical processes like electroplating and electrolysis. Board and competitive exams repeatedly test Nernst equation usage, concentration effects, equilibrium in redox systems, and correct identification of cathode/anode species—so mastering these concepts is essential.
25
Minutes
20
Questions
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Marking
Q1. During electroplating from solution a current of is passed for . The cathodic half‑reaction is . Using and atomic mass of Cu , the mass of copper deposited is:
$0.36\ \mathrm{g}
Q2. For the reaction , given and at , the equilibrium constant for the reaction is closest to:
Q3. Calculate the emf at for the cell . Use and .
Q4. Assertion (A): A concentration cell made of identical electrodes with the same analytical concentration of in both compartments will always show zero emf even if an inert electrolyte (e.g. ) is added to one compartment.
Reason (R): Cell emf depends on ionic activities (effective concentrations); addition of an inert electrolyte can change activity coefficients and thereby can produce a non‑zero emf.
Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Assertion is false but Reason is true.
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
Assertion is true but Reason is false.
Q5. A galvanic cell at is set up as solution containing total silver plus . Ammonia forms the complex with . Using and , the emf of the cell (to two significant figures) is approximately:
Q6. A concentration cell is constructed as at . Calculate the emf of the cell.
Q7. At a galvanic cell is set up as . The measured emf is (the copper half-cell acts as the cathode). What is the pH of the hydrogen half-cell?
Q8. For the reaction , given and at , calculate the equilibrium constant for the reaction.
Q9. An electrolytic cell with inert Pt electrodes contains an aqueous solution initially of CuSO and HSO (assume complete dissociation so ). A current of is passed for minutes. Given and , identify the species reduced at the cathode and calculate the mass of copper deposited (assume 100% coulombic efficiency). Also state the gas evolved at the anode.
Copper is not reduced; of H is produced at cathode and O at anode
Cu is reduced and of Cu is deposited; O evolved at anode
No metal deposition; both H and O evolve in equal amounts
Cu is reduced; of Cu deposited at cathode and O evolved at the anode
Q10. Assertion (A): For a reversible electrochemical cell at constant pressure, if the standard entropy change of the cell reaction is positive, the cell emf increases with temperature.
Reason (R): From and , differentiating with respect to at constant pressure gives .
Both A and R are true and R correctly explains A.
Both A and R are true but R does not correctly explain A.
A is true but R is false.
A is false but R is true.
Q11. A galvanic cell at 298 K is: Zn(s) | Zn^{2+} (0.01 M) || Cu^{2+} (0.10 M) | Cu(s). Given and , calculate the cell potential using the Nernst equation at 298 K.
Q12. A concentration cell is made of hydrogen electrodes: Pt | H(1 atm) | H (10^{-3}\ \mathrm{M}) || H (10^{-6}\ \mathrm{M}) | H(1 atm) | Pt at 298 K. Using the Nernst relation for the hydrogen electrode (), what is the emf of the cell (in volts)?
Q13. At 298 K consider the cell Cu(s) | Cu^{2+} (0.010 M) || AgCl(s) | Ag(s) in a solution where . Given , and , calculate the emf of the cell (assume activities ≈ concentrations and use Nernst equation).
Q14. Assertion (A): For the reduction half-reaction , the reduction potential is much more sensitive to changes in pH than to equal-fold changes in at 298 K.
Reason (R): From the Nernst equation , a tenfold change in changes by , whereas a tenfold change in changes by only .
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is NOT the correct explanation of A.
A is true but R is false.
A is false but R is true.
Q15. During electrolysis of concentrated aqueous NaCl using inert electrodes at near-neutral pH, chlorine gas () is commonly evolved at the anode even though standard potentials are and . Which of the following best explains this observation?
Because is higher than , chloride oxidation is thermodynamically preferred.
Kinetic factors: oxygen evolution has a large overpotential on the anode surface while chloride oxidation is kinetically easier, so evolution occurs despite standard potentials.
High chloride concentration lowers the required potential for formation below that for oxygen evolution by the Nernst shift, so Cl is formed.
Chlorine has a lower standard reduction potential than oxygen, so it is more readily formed.
...and 5 more challenging questions available in the interactive simulator.