2021 O Level Chem P1 Q20 — Qualitative Analysis / Tests for Gases Solution

Answer: A. Lithium first reacts with the water in the solution: 2Li + 2H₂O → 2LiOH + H₂, releasing hydrogen gas and making an alkaline solution of lithium hydroxide. This alkali then displaces ammonia from the ammonium salt: LiOH + NH₄Cl → LiCl + H₂O + NH₃.

So two gases are produced — hydrogen and ammonia. Ammonia is alkaline, so it turns moist red litmus blue (blue litmus stays blue → no change). Hydrogen burns with a squeaky ‘pop’ when a burning splint is applied. Neither gas relights a glowing splint — only oxygen does that.

Row A matches all four observations: red litmus turns blue, blue litmus no change, a ‘pop’ with a burning splint, and no change with a glowing splint.