JEE Main 2023 · 12 April · morning · Single correct · +4 / −1
In the given reaction cycle
CaCl₂ + Na₂CO₃ @>>> X @. + Y ; @AAA @VVV @. ; @<Z<< @.
X, Y and Z respectively are :
- (a) X, Y, Z; CaCO₃, NaCl, KCl
- (b) X, Y, Z; CaO, NaCl+CO₂, NaCl
- (c) X, Y, Z; CaCO₃, NaCl, HCl
- (d) X, Y, Z; CaO, NaCl+CO₂, KCI
Answer and solution
Answer (c) X, Y, Z; CaCO₃, NaCl, HCl
Solution
Chemistry ma’am · 4 steps
Mixing the salts precipitates CaCO₃, and only an acid like HCl turns it back into CaCl₂.
- Forward reaction. CaCl₂ and Na₂CO₃ swap partners in a double displacement. Calcium carbonate is insoluble, so it comes out as a white precipitate and sodium chloride stays in solution.
CaCl₂ + Na₂CO₃ → CaCO₃ v + 2NaCl
- Identify X and Y. So X is CaCO₃ and Y is NaCl. No CaO or CO₂ forms here. That would need strong heating of CaCO₃, not just mixing two solutions.
- Close the cycle. Z must convert CaCO₃ back into CaCl₂. A carbonate reacts with an acid: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ ↑. Neutral salts like NaCl or KCl cannot dissolve CaCO₃.
- So. X is CaCO₃, Y is NaCl and Z is HCl, which is option (c).
The idea to keep. In a reaction cycle, the reagent that closes the loop must actually react. An insoluble carbonate returns to the soluble chloride only with an acid such as HCl, which releases CO₂.
Answer from the NTA final answer key. Solution by PrepWiser.