Questions-block / thermal stability
Which one of the following is the correct order of thermal stabilities of metal carbonates?
- (a) BaCO₃ > CaCO₃ > MgCO₃ > BeCO₃
- (b) BaCO₃ > MgCO₃ > CaCO₃ > BeCO₃
- (c) CaCO₃ > BaCO₃ > MgCO₃ > BeCO₃
- (d) BaCO₃ > BeCO₃ > MgCO₃ > CaCO₃
Answer: (a) BaCO₃ > CaCO₃ > MgCO₃ > BeCO₃
Larger cation → less polarisation of CO₃²⁻ → more stable carbonate. Down group 2 stability rises: BaCO₃ > SrCO₃ > CaCO₃ > MgCO₃ > BeCO₃ → (a). BeCO₃ is so unstable it is kept under CO₂.