O Levels Chemistry (5070)•5070/12/M/J/20
Explanation
Ammonia Gas Liberation from Ammonium Salts Steps:
- Ammonium nitrate (NH₄NO₃) dissociates in water to NH₄⁺ and NO₃⁻ ions.
- Strong bases like hydroxides react with NH₄⁺ to form ammonia gas upon warming.
- The reaction is NH₄⁺ + OH⁻ → NH₃↑ + H₂O.
- Potassium hydroxide (KOH) supplies OH⁻ ions for this decomposition.
Why B is correct:
- KOH, a strong base, reacts with NH₄NO₃ to liberate NH₃: NH₄NO₃ + KOH → KNO₃ + NH₃ + H₂O (on warming), per the standard ammonium salt-base reaction.
Why the others are wrong:
- A. Calcium nitrate: Neutral salt; no OH⁻ ions to decompose NH₄⁺.
- C. Sodium chloride: Inert neutral salt; no reaction with NH₄NO₃.
- D. Sulfuric acid: Strong acid; protonates NH₃ to form NH₄⁺, preventing liberation.
Final answer: B
Topic: The characteristic properties of acids and bases
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