A-LevelChemistryEquilibriaMay/June 2016Paper 1 Q151 Mark
Ammonia gas, NH₃, and hydrogen sulfide gas, H₂S, react together to form the salt ammonium sulfide, (NH₄)₂S. Ammonium sulfide dissolves in water to produce an orange alkaline solution. (NH₄)₂S(aq) ⇌ NH₃(aq) + NH₄SH(aq) The addition of NaOH(aq) to this solution produces a gas, X. The addition of HCl(aq) to a separate portion of this solution produces a gas, Y. What are the identities of X and Y? X Y H₂S H₂S H₂S NH₃ NH₃ H₂S NH₃ NH₃
AH₂S H₂S
BH₂S NH₃
CNH₃ H₂S
DNH₃ NH₃
✓ Correct Answer
The correct answer is C: NH₃ H₂S
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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