When we heat lead nitrate [Pb(N03)2] in a boiling tube, we observe the emission of brown fumes. Which one of the following is the brown gas?

examrobotsa's picture

Submitted by examrobotsa on

Q: (CDS-I/2021)
When we heat lead nitrate [Pb(N03)2] in a boiling tube, we observe the emission of brown fumes.
Which one of the following is the brown gas?

question_subject: 

Science

question_exam: 

CDS-I

stats: 

0,15,17,3,8,6,15

keywords: 

{'brown fumes': [0, 0, 0, 1], 'n03': [0, 0, 0, 1], 'n02': [0, 0, 0, 1], 'emission': [0, 0, 4, 5], 'gas': [9, 1, 9, 27], 'n202': [0, 0, 0, 1], 'tube': [1, 1, 0, 2]}

When lead nitrate (Pb(NO3)2) is heated in a boiling tube, the emission of brown fumes is observed. One of the options provided as the brown gas is NO2 (nitrogen dioxide), which is the correct answer.

To understand why NO2 is the correct answer, we need to look at the chemical reaction that occurs when lead nitrate is heated. Lead nitrate decomposes upon heating to form lead oxide (PbO), nitrogen dioxide (NO2), and oxygen gas (O2).

The chemical equation for this reaction is:

2Pb(NO3)2(s) [REPLACEMENT] 2PbO(s) + 4NO2(g) + O2(g)

From this equation, it is clear that the brown gas observed is NO2. Nitrogen dioxide is a brown gas with a pungent odor.

Option 1, NO (nitric oxide), is not the brown gas observed. Nitric oxide is a colorless gas.

Options 2 and 3, N2O2 (dinitrogen tetroxide) and NO3 (nitrate), are not the brown gas observed either. N2O2 is a colorless gas, and NO3 refers to the nitrate ion, not

Practice this on app