Question

The thermal stability of alkaline earth metal carbonates-$MgC{{O}_{3}},CaC{{O}_{3}},SrC{{O}_{3}}$ and $BaC{{O}_{3}}$ follows the order:
(A) $BaC{{O}_{3}}>SrC{{O}_{3}}>CaC{{O}_{3}}>MgC{{O}_{3}}$
(B) $CaC{{O}_{3}}>SrC{{O}_{3}}>MgC{{O}_{3}}>BaC{{O}_{3}}$
(C) $MgC{{O}_{3}}>CaC{{O}_{3}}>SrC{{O}_{3}}>BaC{{O}_{3}}$
(D) $BaC{{O}_{3}}>SrC{{O}_{3}}>MgC{{O}_{3}}>CaC{{O}_{3}}$

Answer 1

Hint: Thermal stability of alkaline earth metal carbonates increases with cationic size. All carbonates undergo thermal decomposition to form the metal oxide and carbon dioxide. Thermal stability of alkaline earth metal carbonates increases on moving down the group.

Complete step by step solution:
-Ionic size of alkaline earth metals increase in order Mg, Ca, Sr, Ba. Barium has the largest ionic radius.
-Smaller the size of cation, higher is charge density as alkaline earth metals have a charge as +2.
-More the charge density, the greater effect it has on carbonate ions.
-As the size of alkaline earth metal ions increases across the group, the effect of ions on carbonate ions decreases.
-So more heat must be supplied in order to remove carbon dioxide to leave metal oxide.
-On heating alkaline earth metal carbonates undergo thermal decomposition to form a metal oxide and carbon dioxide.
-More heat supplied, carbonates become more thermally stable.
-As Barium has the largest ionic radius, it has the least effect on carbonate ion, so more heat is supplied to remove carbon dioxide to produce Barium Oxide.
-Thermal stability of alkaline earth metal carbonates increases on moving down the group.

Hence, the thermal stability of alkaline earth metal carbonates-$MgC{{O}_{3}},CaC{{O}_{3}},SrC{{O}_{3}}$ and \[BaC{{O}_{3}}\]follows the order:
(A) $BaC{{O}_{3}}>SrC{{O}_{3}}>CaC{{O}_{3}}>MgC{{O}_{3}}$

Note: Alkaline earth metals belong to group 2 of the periodic table and are s block elements. These elements have two electrons in s orbital of the valence shell. The electropositive character of alkaline earth metal increases on moving down the group. Thermal stability of alkaline earth metal carbonates increases on moving down the group