Question:
Which one of the carbonates is unstable in air and is kept in $CO_{2}$ atmosphere to avoid decomposition?
Which one of the carbonates is unstable in air and is kept in $CO_{2}$ atmosphere to avoid decomposition?
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Smallest cation ($Be^{2+}$) leads to highest polarizing power, causing the lowest thermal stability among group 2 carbonates.
Updated On: Jun 3, 2026
- $MgCO_{3}$
- $CaCO_{3}$
- $BaCO_{3}$
- $BeCO_{3}$
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The Correct Option is D
Solution and Explanation
Step 1: Concept
The thermal stability of alkaline earth metal carbonates increases down the group as the size of the metal cation increases, reducing its polarizing power.
Step 2: Meaning
A highly polarizing small cation distorts the large oxygen electron cloud of the carbonate ion ($CO_{3}^{2-}$), making it break down into its corresponding oxide and carbon dioxide gas easily.
Step 3: Analysis
$Be^{2+}$ is the smallest cation in Group 2 and exerts a high polarizing action on the carbonate group. Because of this, $BeCO_{3}$ is highly unstable and decomposes even at room temperature. To prevent this reverse reaction and maintain it, it must be stored in a $CO_{2}$-rich atmosphere.
Step 4: Conclusion
Therefore, $BeCO_{3}$ is the specific carbonate that requires a $CO_{2}$ atmosphere to prevent spontaneous decomposition.
Final Answer: (D)
The thermal stability of alkaline earth metal carbonates increases down the group as the size of the metal cation increases, reducing its polarizing power.
Step 2: Meaning
A highly polarizing small cation distorts the large oxygen electron cloud of the carbonate ion ($CO_{3}^{2-}$), making it break down into its corresponding oxide and carbon dioxide gas easily.
Step 3: Analysis
$Be^{2+}$ is the smallest cation in Group 2 and exerts a high polarizing action on the carbonate group. Because of this, $BeCO_{3}$ is highly unstable and decomposes even at room temperature. To prevent this reverse reaction and maintain it, it must be stored in a $CO_{2}$-rich atmosphere.
Step 4: Conclusion
Therefore, $BeCO_{3}$ is the specific carbonate that requires a $CO_{2}$ atmosphere to prevent spontaneous decomposition.
Final Answer: (D)
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