When we heat lead nitrate [Pb(NO₃)₂] in a boiling tube, we observe the

When we heat lead nitrate [Pb(NO₃)₂] in a boiling tube, we observe the emission of brown fumes. Which one of the following is the brown gas ?

[amp_mcq option1=”NO” option2=”N₂O₂” option3=”NO₃” option4=”NO₂” correct=”option4″]

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UPSC CDS-1 – 2021

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When lead nitrate [Pb(NO₃)₂] is heated, it undergoes thermal decomposition, producing lead(II) oxide (PbO), oxygen gas (O₂), and nitrogen dioxide gas (NO₂). The brown fumes observed are due to nitrogen dioxide (NO₂).

– The balanced chemical equation for the decomposition of lead nitrate is: 2Pb(NO₃)₂(s) → 2PbO(s) + 4NO₂(g) + O₂(g).
– Nitrogen dioxide (NO₂) is a toxic, reddish-brown gas.

– Nitrogen monoxide (NO) is a colourless gas.
– N₂O₂ is a dimer of NO, and while related to nitrogen oxides, it is not the species responsible for the prominent brown fumes in this decomposition.
– NO₃ is a highly reactive radical and not the stable product gas observed as brown fumes.

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