Question

Identify the formula of compound (B) formed in the following reactions:
(i) Lanthanoids (Ln) burn in oxygen forming compound (A).
(ii) Compound (A) reacts with excess \(\mathrm{CO_2}\) to form compound (B).

• A. \(\mathrm{LnO_2}\)
• B. \(\mathrm{Ln_2CO_3}\)
• C. \(\mathrm{Ln_3(CO_3)_2}\)
• D. \(\mathrm{Ln_2(CO_3)_3}\)

Hint:

Lanthanoids predominantly form +3 oxidation state compounds such as oxides \(\mathrm{Ln_2O_3}\) and carbonates \(\mathrm{Ln_2(CO_3)_3}\).

Answer 1

The Correct Option is D

Step 1: Reaction of lanthanoids with oxygen.
Lanthanoids generally exhibit a +3 oxidation state and burn in oxygen to form their oxides: \[ 4\mathrm{Ln} + 3\mathrm{O_2} \rightarrow 2\mathrm{Ln_2O_3} \]

Step 2: Reaction of oxide with carbon dioxide.
Basic metal oxides react with excess \(\mathrm{CO_2}\) to form metal carbonates.

Step 3: Formation of carbonate.
\[ \mathrm{Ln_2O_3} + 3\mathrm{CO_2} \rightarrow \mathrm{Ln_2(CO_3)_3} \]

Step 4: Conclusion.
Thus, compound (B) formed is \(\mathrm{Ln_2(CO_3)_3}\).