When lead nitrate [Pb(NO₃)₂] is heated, two key observations are: (1) yellow residue of lead monoxide (PbO) forms in the test tube; (2) brown fumes of nitrogen dioxide (NO₂) gas are released, along with oxygen gas. This is a thermal decomposition reaction and a classic example in NCERT Class 10 Chemistry.
When lead nitrate [Pb(NO₃)₂] is heated: yellow residue of PbO forms + brown fumes of NO₂.
Reaction: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂.
PbO = yellow solid (lead monoxide); NO₂ = reddish-brown gas (nitrogen dioxide).
Also observed: crackling sound (decrepitation) + O₂ gas (relights glowing splint).
Type: thermal decomposition reaction.
NCERT Class 10 Science Chapter 1 — Chemical Reactions and Equations.
Chemical Reaction: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
(Lead nitrate → Lead monoxide + Nitrogen dioxide + Oxygen)
Two Observations:
Yellow/orange-yellow residue is formed in the test tube. • This is Lead Monoxide (PbO) • PbO is a yellow solid • The white crystals of Pb(NO₃)₂ change to a yellow solid
Brown fumes are evolved (given off). • The brown gas is Nitrogen Dioxide (NO₂) • NO₂ is a reddish-brown, pungent gas • Also note: a crackling sound (decrepitation) is heard when heating begins
All Observations (Complete):
| Observation | Explanation |
|---|---|
| Yellow residue | PbO (Lead Monoxide) formed |
| Brown fumes | NO₂ (Nitrogen Dioxide) gas released |
| Crackling sound | Decrepitation (crystal structure breaking) |
| Oxygen gas | O₂ also released (colourless, relights glowing splint) |
Type of Reaction: • Thermal Decomposition Reaction: A single compound breaks down into two or more products on heating • 2Pb(NO₃)₂ → 2PbO + 4NO₂↑ + O₂↑
Test for Oxygen: • A glowing wooden splint held near the mouth of the tube relights → confirms O₂ production
Test for NO₂: • Brown colour and pungent smell • Turns moist starch iodide paper blue (NO₂ is an oxidising agent)
Safety Note: • NO₂ is a toxic gas; heating should be done in a fume hood • Wear eye protection
NCERT: Class 10 Science Chapter 1 — Chemical Reactions and Equations
When lead nitrate [Pb(NO₃)₂] is heated: (1) A yellow/orange-yellow residue of lead monoxide (PbO) forms. (2) Brown fumes of nitrogen dioxide (NO₂) are evolved. Additional observations: crackling sound (decrepitation) and oxygen gas released (which relights a glowing splint). Reaction: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂. It is a thermal decomposition reaction. (NCERT Class 10 Science, Chapter 1)
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