Galvanic Cells

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

1. CSCA Chemistry December 2025 Past Paper
   Scientists developed a room-temperature Na-O₂ rechargeable battery. NaClO₄ is dissolved in an organic solvent as the electrolyte. Metallic sodium and Pt/C-loaded carbon cloth are used as electrode materials. The overall cell reaction is: O₂ + 2Na = Na₂O₂. Which statement is correct? ( )
   • A. During discharge, ClO₄- moves toward the positive electrode
   • B. During discharge, O₂ is released; during charge, O₂ is absorbed
   • C. During discharge, the negative electrode reaction is: Na+ + e- → Na
   • D. During charge, the positive electrode reaction is: Na₂O₂ - 2e- → 2Na+ + O₂
   Show answer & solution

   Answer: D

   Answer: D Discharge: Na is oxidized at the negative electrode, Na − e⁻ → Na⁺, and O₂ is reduced to form Na₂O₂. Charging reverses this: Na₂O₂ loses electrons at the positive electrode and releases O₂, so the positive electrode reaction is Na₂O₂ − 2e⁻ → 2Na⁺ + O₂.
   See it in the full CSCA Chemistry December 2025 Past Paper
2. CSCA Chemistry March 2026 Past Paper
   $\mathrm { Pb } + \mathrm { PbO } _ { 2 } + 2 \mathrm { H } _ { 2 } \mathrm { SO } _ { 4 } \rightleftharpoons 2 \mathrm { PbSO } _ { 4 } + 2 \mathrm { H } _ { 2 } \mathrm { O }$. Which is correct?
   • A．During discharge, $\mathrm { PbO } _ { 2 }$ undergoes reduction
   • B．During discharge, cathode reaction: $\mathrm { Pb } ^ { 2 + } + 2 \mathrm { e } ^ { - } \rightarrow \mathrm { Pb }$
   • C．During charging, anode connects to power source's negative terminal
   • D．During charging, $\left[ \mathrm { H } ^ { + } \right]$in solution increases
   Show answer & solution

   Answer: A

   Discharge: $\mathrm { PbO } _ { 2 }$ at cathode, $\mathrm { Pb } ( + 4 \rightarrow + 2 )$ gains electrons $=$ reduction $\checkmark$. $\mathrm { B }$ : anode is oxidation. C: anode connects to positive terminal. Answer: A.
   Take the full CSCA Chemistry March 2026 Past Paper — timed & graded