Identify both the reducing agent and the number of electrons transferred in the following reaction.

3 PbO(s) + 2 NH3(aq) ⇌ 3 Pb(s) + N2(g) + 3 H2O(l)

Question

Identify both the reducing agent and the number of electrons transferred in the following reaction.

3 PbO(s) +  2 NH3(aq) ⇌ 3 Pb(s) + N2(g)  +  3 H2O(l)

BlackTom AI · Accepted Answer

To tackle this redox question, I will first restate the reaction and list the options, then evaluate each choice one by one.
Option 1: 'PbO is the reducing agent and 2 electrons have been transferred.' In this reaction, PbO goes from Pb(II) in PbO to Pb(0) in Pb(s), which is a gain of electrons (reduction) for lead. Therefore PbO is not the reducing agent; it is the oxidizing agent. This makes the claim about PbO as the reducing agent incorrect, and the reported 2 electrons transferred does not match the actual electron transfer if any is considered here.
Option 2: 'PbO is the reducing agent and 6 electrons have been transferred.' For PbO to be the reducing agent, PbO would have to be oxidized (lose electrons). However, PbO is reduced to Pb(s) in the reaction, meaning it accepts electrons rather than donates them. Thus the assertion that PbO is the reducing agent is false. The 6-electron transfer count is tied to the oxidation state changes of nitrogen in NH3 to N2, not to PbO; but since the reducing agent is misidentified, this whole option is incorrect.
Option 3: 'NH3 is the reducing agent and 2 electrons have been transferred.' Here, NH3 acts as the reducing agent by donating electrons to the oxidized species (PbO). However, the electron transfer count of 2 electrons is inconsistent with the change in oxidation state of nitrogen from −3 in NH3 to 0 in N2, which involves 6 electrons per N2 formed (two NH3 molecules collectively transfer 6 electrons). Therefore this option is incorrect both in identifying NH3 as the reducing agent in isolation and in the electron-count.
Option 4: 'NH3 is the reducing agent and 6 electrons have been transferred.' This option correctly identifies NH3 as the reducing agent, since nitrogen is oxidized from −3 in NH3 to 0 in N2, meaning NH3 donates electrons to the oxidized PbO. The overall process involves the transfer of 6 electrons (two NH3 molecules each losing 3 electrons, totaling 6) to reduce PbO to Pb. This matches the stoichiometry of the reaction and the typical electron accounting for N2 formation from NH3.
Option 5: 'I am unsure and need to study this concept to prepare for the exam.' While honesty is fine, this option does not provide a chemical reasoning or conclusion about the redox process, so it is not a correct answer.
Summarizing the reasoning across all options, the incorrect choices fail because they misidentify which species is oxidized/reduced or miscount the electron transfer. The correct understanding is that NH3 is the reducing agent, and 6 electrons are transferred in the overall reaction due to the oxidation of nitrogen from −3 in NH3 to 0 in N2.

CHEM 1220 SP2025 (18215) CHEM 1220 Practice Exam #4 v2 (17.4 - 17.6, 19, 20.1 - 20.5)- Requires Respondus LockDown Browser

Identify both the reducing agent and the number of electrons transferred in the following reaction. 3 PbO(s) + 2 NH3(aq) ⇌ 3 Pb(s) + N2(g) + 3 H2O(l)

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