Question:
When lithium nitrate and calcium nitrate are heated in separate test tubes, which of the following observations would be identical for both?
When lithium nitrate and calcium nitrate are heated in separate test tubes, which of the following observations would be identical for both?
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Remember:
\[
LiNO_3
\]
behaves abnormally among alkali metal nitrates and decomposes like alkaline earth metal nitrates.
Updated On: Jun 17, 2026
- Evolution of colorless, non-flammable gas
- Evolution of brown fumes and gas that supports combustion
- The formation of a metal that reacts vigorously with water
- Gases are not liberated
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The Correct Option is B
Solution and Explanation
Concept:
Thermal decomposition of nitrates depends upon the nature of the metal cation.
Different nitrates decompose differently:
• Alkali metal nitrates generally form nitrites and oxygen
• Lithium nitrate behaves abnormally
• Alkaline earth metal nitrates form metal oxides, nitrogen dioxide and oxygen
The decomposition products help identify experimental observations.
Step 1: Write thermal decomposition of lithium nitrate. Lithium nitrate behaves differently from other alkali metal nitrates. On heating: \[ 4LiNO_3 \rightarrow 2Li_2O + 4NO_2 + O_2 \] Observations:
• Brown fumes of \(NO_2\)
• Oxygen gas released
• Oxygen supports combustion
Step 2: Write thermal decomposition of calcium nitrate. On heating: \[ 2Ca(NO_3)_2 \rightarrow 2CaO + 4NO_2 + O_2 \] Again the products are:
• Brown fumes of nitrogen dioxide
• Oxygen gas
Step 3: Analyse the gases evolved. Nitrogen dioxide: \[ NO_2 \] is a brown coloured gas. Oxygen: \[ O_2 \] supports combustion. Thus both nitrates show:
• Brown fumes
• Gas supporting combustion
Step 4: Eliminate incorrect options. Option (A):
• Incorrect because brown fumes are evolved
Option (C):
• No free metal is produced
Option (D):
• Incorrect because gases are evolved
Step 5: Write the final answer. Thus identical observation is: \[ \boxed{\text{Evolution of brown fumes and gas that supports combustion}} \] Therefore, the correct option is: \[ \boxed{(B)} \]
• Alkali metal nitrates generally form nitrites and oxygen
• Lithium nitrate behaves abnormally
• Alkaline earth metal nitrates form metal oxides, nitrogen dioxide and oxygen
The decomposition products help identify experimental observations.
Step 1: Write thermal decomposition of lithium nitrate. Lithium nitrate behaves differently from other alkali metal nitrates. On heating: \[ 4LiNO_3 \rightarrow 2Li_2O + 4NO_2 + O_2 \] Observations:
• Brown fumes of \(NO_2\)
• Oxygen gas released
• Oxygen supports combustion
Step 2: Write thermal decomposition of calcium nitrate. On heating: \[ 2Ca(NO_3)_2 \rightarrow 2CaO + 4NO_2 + O_2 \] Again the products are:
• Brown fumes of nitrogen dioxide
• Oxygen gas
Step 3: Analyse the gases evolved. Nitrogen dioxide: \[ NO_2 \] is a brown coloured gas. Oxygen: \[ O_2 \] supports combustion. Thus both nitrates show:
• Brown fumes
• Gas supporting combustion
Step 4: Eliminate incorrect options. Option (A):
• Incorrect because brown fumes are evolved
Option (C):
• No free metal is produced
Option (D):
• Incorrect because gases are evolved
Step 5: Write the final answer. Thus identical observation is: \[ \boxed{\text{Evolution of brown fumes and gas that supports combustion}} \] Therefore, the correct option is: \[ \boxed{(B)} \]
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