JEE Main · 2019 · 12 Apr 2019 · Shift 1 · s-Block Elements

The correct sequence of thermal stability of the following carbonates is :

(A) $BaCO_{3} < SrCO_{3} < CaCO_{3} < MgCO_{3}$
(B) $BaCO_{3} < CaCO_{3} < SrCO_{3} < MgCO_{3}$
(C) $MgCO_{3} < CaCO_{3} < SrCO_{3} < BaCO_{3}$ ✓ Correct
(D) $MgCO_{3} < SrCO_{3} < CaCO_{3} < BaCO_{3}$

Answer: (C)

Solution

Thermal stability of the group-2 carbonates rises as the cation grows. A small, highly polarising cation distorts the carbonate ion and helps it break down, while a large cation polarises it little and leaves it intact. Since the cation size increases

Mg X^{2 +} < Ca X^{2 +} < Sr X^{2 +} < Ba X^{2 +}

, the stability order is

MgCO X_{3} < CaCO X_{3} < SrCO X_{3} < BaCO X_{3}

JEE Main · 2019 · 12 Apr 2019 · Shift 1 · Single correct option

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