When lead nitrate is heated, a brown gas evolves and a solid residue remains. Which explanation is correct?
Answer and explanation
Correct answer: The brown gas is nitrogen dioxide, the solid residue is lead oxide, and oxygen is also evolved.
Lead nitrate undergoes thermal decomposition on heating:
\[
2\mathrm{Pb(NO_3)_2} \xrightarrow{\Delta} 2\mathrm{PbO} + 4\mathrm{NO_2} + \mathrm{O_2}
\]
\(\mathrm{NO_2}\) is the brown gas, and \(\mathrm{PbO}\) is the solid residue. Although \(\mathrm{O_2}\) is also formed, it is colourless, so it cannot be the brown gas.
Frequently asked questions
What is the correct answer to this question?
The brown gas is nitrogen dioxide, the solid residue is lead oxide, and oxygen is also evolved.
Why is this the correct answer?
Lead nitrate undergoes thermal decomposition on heating:
\[
2\mathrm{Pb(NO_3)_2} \xrightarrow{\Delta} 2\mathrm{PbO} + 4\mathrm{NO_2} + \mathrm{O_2}
\]
\(\mathrm{NO_2}\) is the brown gas, and \(\mathrm{PbO}\) is the solid residue. Although \(\mathrm{O_2}\) is also formed, it is colourless, so it cannot be the brown gas.
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.
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