Question

Which of the following metal carbonates decomposes on heating ?

• A. $L{i}_{2}C{O}_3$
• B. $N{a}_{2}C{O}_3$
• C. $K_{2}C{O}_3$
• D. $MgC{O}_3$

Answer 1

Answer: (A), (D)

$MgC{O}_3$
$L{i}_{2}C{O}_3$

Lithium carbonate and magnesium carbonate are thermally unstable. They decompose on heating. Properties of Li are similar to Mg because of diagonal relationship.

Li2​CO3​ → Li2​O + CO2​

MgCO3​ → MgO + CO2​

Li2​CO3​ and MgCO3​ are salts of weak acid CO2​ with weak bases LiOH and Mg(OH)2​. On the other hand, NaOH and KOH are much stronger bases and can hold the CO2​ easily. Thus, sodium carbonate and potassium carbonate are thermally stable. They do not decompose on heating.

Thus, options A and D are correct.