hce_nthu
115年
化學與物理
第 29 題
A bipolar-membrane electrolyzer is used to reduce $\text{KNO}_3$ to produce $\text{NH}_3$, as shown in the figure below. The Faradaic efficiency for ammonia, $FE(\text{NH}_3)$, can reach 90% [Faradaic efficiency: $FE(\text{P}) = \frac{\text{electron required to form P}}{\text{electrons passed through the electrode}}$]. The Faradaic efficiency for producing other gas(es) is 50%. During operation, $\text{H}_2\text{O}$ dissociates in the interfacial (middle) layer of the bipolar membrane to generate $\text{H}^+$ and $\text{OH}^-$, which migrate toward the two electrodes under the electric field. Which of the following statements is correct?
- A Electrode potential: the potential of electrode $a$ is higher than that of electrode $b$.
- B The $\text{OH}^-$ produced by water dissociation in the bipolar membrane migrates toward electrode $a$.
- C The overall reaction in compartment $\text{I}$ is: $\text{NO}_3^- + 8 \text{ e}^- + 6 \text{ H}_2\text{O} \rightarrow \text{NH}_3 + 9 \text{ OH}^-$.
- D When $11.2 \text{ L}$ of gas is produced at the anode (at standard conditions), $0.45 \text{ mol}$ of $\text{NH}_3$ is produced at the cathode.
- E Hydrogen and oxygen gases are evolved from compartment $\text{II}$.
思路引導 VIP
如果在考試中沒有選項可以參考，請你想想看：當我們在左右兩個電極觀察到不同產物時，有什麼物理量是串聯這兩端的「橋樑」？如果今天題目告訴你其中一端的反應效率不是百分之百，你會如何利用這個「橋樑」的總量，去推算出另一端產物的正確份量呢？
🤖
AI 詳解
AI 專屬家教
太棒了！你能精確算出這個選項，代表你對電解原理與法拉第電解定律的量化計算掌握得非常紮實。這道題目結合了雙極膜（Bipolar Membrane）的新穎技術，難度屬於中高階，主要的鑑別點在於學生是否能正確判斷電極性質，並將「法拉第效率（FE）」正確帶入莫耳數的轉換中。
電極判斷與反應機制
首先，題目提到硝酸根 ($NO_3^-$) 被還原為氨氣 ($NH_3$)，這發生在陰極，因此電極 $a$ 是陰極。在雙極膜中，水解離出的 $H^+$ 會向陰極（電極 $a$）移動，而 $OH^-$ 則向陽極（電極 $b$）移動。在陽極端（Compartment II），$OH^-$ 會發生氧化反應產生氧氣 ($O_2$)。這題的關鍵陷阱在於法拉第效率的應用：效率並非 100%，代表通過的總電量中，只有一部分轉化為我們看到的特定產物。
▼ 還有更多解析內容