Why is it incorrect to identify the brown fumes evolved on heating lead nitrate as oxygen?
Answer and explanation
Correct answer: Oxygen is colourless; the brown fumes are nitrogen dioxide.
Thermal decomposition of lead nitrate produces lead(II) oxide, nitrogen dioxide, and oxygen: \(2\mathrm{Pb(NO_3)_2} \xrightarrow{\Delta} 2\mathrm{PbO} + 4\mathrm{NO_2} + \mathrm{O_2}\). \(\mathrm{NO_2}\) is a brown gas, whereas \(\mathrm{O_2}\) is colourless. Therefore, the visible brown fumes are nitrogen dioxide, not oxygen. Oxygen is confirmed by its ability to relight a glowing splint.
Frequently asked questions
What is the correct answer to this question?
Oxygen is colourless; the brown fumes are nitrogen dioxide.
Why is this the correct answer?
Thermal decomposition of lead nitrate produces lead(II) oxide, nitrogen dioxide, and oxygen: \(2\mathrm{Pb(NO_3)_2} \xrightarrow{\Delta} 2\mathrm{PbO} + 4\mathrm{NO_2} + \mathrm{O_2}\). \(\mathrm{NO_2}\) is a brown gas, whereas \(\mathrm{O_2}\) is colourless. Therefore, the visible brown fumes are nitrogen dioxide, not oxygen. Oxygen is confirmed by its ability to relight a glowing splint.
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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