JEE Main 2022 · 29 July · morning · Single correct · +4 / −1
Lithium nitrate and sodium nitrate, when heated separately, respectively, give :
- (a) LiNO₂ and NaNO₂
- (b) Li₂ O and Na₂ O
- (c) Li₂ O and NaNO₂
- (d) LiNO₂ and Na₂ O
Answer and solution
Answer (c) Li₂ O and NaNO₂
Solution
Chemistry ma’am · 3 steps
Lithium behaves like magnesium, not like its own group: its nitrate breaks all the way down to the oxide.
- Lithium nitrate. Li⁺ is tiny and strongly polarising, and Li₂O has a very high lattice energy. So LiNO₃ decomposes fully to the oxide, giving off NO₂ and O₂, just as Mg(NO₃)₂ does.
4LiNO₃ →(Δ) 2Li₂O + 4NO₂ + O₂
- Sodium nitrate. Na⁺ is larger and polarises the nitrate ion much less. On heating, NaNO₃ only loses oxygen and stops at the nitrite.
2NaNO₃ →(Δ) 2NaNO₂ + O₂
- So. Heating gives Li₂O from lithium nitrate and NaNO₂ from sodium nitrate, which is option (c).
The idea to keep. Lithium is the odd one out in Group 1 and copies magnesium (diagonal relationship). LiNO₃ gives the oxide; NaNO₃, KNO₃ and the heavier alkali nitrates stop at the nitrite.
Answer from the NTA final answer key. Solution by PrepWiser.