Why is it incorrect to identify the brown fumes observed on heating lead nitrate as oxygen?
Answer and explanation
Correct answer: The brown fumes are nitrogen dioxide, whereas oxygen is colourless.
Thermal decomposition of lead nitrate produces brown nitrogen dioxide gas as well as colourless oxygen:
\(2\mathrm{Pb(NO_3)_2} \xrightarrow{\Delta} 2\mathrm{PbO}+4\mathrm{NO_2}+\mathrm{O_2}\).
Therefore, the visible brown fumes are \(\mathrm{NO_2}\), not oxygen. Oxygen is indeed formed in the reaction, but it is colourless and cannot be identified as brown fumes.
Frequently asked questions
What is the correct answer to this question?
The brown fumes are nitrogen dioxide, whereas oxygen is colourless.
Why is this the correct answer?
Thermal decomposition of lead nitrate produces brown nitrogen dioxide gas as well as colourless oxygen:
\(2\mathrm{Pb(NO_3)_2} \xrightarrow{\Delta} 2\mathrm{PbO}+4\mathrm{NO_2}+\mathrm{O_2}\).
Therefore, the visible brown fumes are \(\mathrm{NO_2}\), not oxygen. Oxygen is indeed formed in the reaction, but it is colourless and cannot be identified as brown fumes.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Chemical Reactions and Equations.
