When lead nitrate is heated strongly, brown fumes are produced along with a solid residue and oxygen gas. (i) Name the brown gas evolved. (ii) What type of decomposition reaction is this?
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
(i) The brown gas evolved is nitrogen dioxide (NO₂).
(ii) This is a thermal decomposition reaction, as the decomposition is caused by heat.
The reaction is:
$$2\text{Pb(NO}_3)_2(s) \xrightarrow{\text{Heat}} 2\text{PbO}(s) + 4\text{NO}_2(g) + \text{O}_2(g)$$
Source: Chapter 1, Section 1.2.2 Decomposition Reaction (Activity 1.6)
---
Explanation
- (i) is straightforward — the textbook explicitly states "These fumes are of nitrogen dioxide (NO₂)." Write the name and formula for full credit.
- (ii) The key term examiners look for is thermal decomposition (not just "decomposition"), because the energy source is heat. Writing the balanced equation earns the second mark and demonstrates understanding of the reaction type.