Question

On heating which of the following releases ${CO_2}$ most easily ?

• A. ${MgCO3 }$
• B. ${CaCO3 }$
• C. ${K2CO3 }$
• D. ${Na2CO3 }$

Answer 1

The Correct Option is A

To determine which compound releases ${CO_2}$ most easily upon heating, we need to consider the thermal stability of the carbonates given in the options. The thermal stability of carbonates decreases down the group in the periodic table. Therefore, alkaline earth metal carbonates like ${MgCO_3}$ and ${CaCO_3}$ are generally less stable than alkali metal carbonates like ${K_2CO_3}$ and ${Na_2CO_3}$.

Here's the step-by-step reasoning:

1. Decomposition Reaction:
   Carbonates decompose upon heating to release ${CO_2}$ gas:
   • ${MgCO_3 \rightarrow MgO + CO_2}$
   • ${CaCO_3 \rightarrow CaO + CO_2}$
   • Alkali metal carbonates such as ${K_2CO_3}$ and ${Na_2CO_3}$ do not decompose easily on heating to release ${CO_2}$ under normal conditions.
2. Analysis of Stability:
   Among the alkaline earth metal carbonates, ${MgCO_3}$ is less stable compared to ${CaCO_3}$ because magnesium is lighter and has a smaller ionic radius compared to calcium. As a result, ${MgCO_3}$ decomposes at a lower temperature.
3. Conclusion:
   Given that alkali metal carbonates are typically very stable and do not decompose easily, and that ${MgCO_3}$ decomposes more readily than ${CaCO_3}$, the compound that releases ${CO_2}$ most easily upon heating is ${MgCO_3}$.

Therefore, the correct answer is ${MgCO_3}$.