Galvanic Cells

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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
   ดูคำตอบและวิธีทำ

   คำตอบ: 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.
   ดูในชุดข้อสอบเต็ม 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
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   คำตอบ: 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.
   ทำข้อสอบเต็มชุด CSCA Chemistry March 2026 Past Paper — จับเวลาและให้คะแนน