Predict what would be observed (and why) from an aqueous mixture for each of the following (all substances are water soluble). a.) potassium carbonate and hydrochloric acid: The reaction will cause carbon dioxide bubbles b.) zinc chloride and silver nitrate: The reaction will cause a white precipitate c.) magnesium chloride and sodium hydroxide: The reaction will cause a white precipitate d.) ammonium nitrate and sodium hydroxide:
The correct answer and explanation is:
Correct Answer for (d):
The reaction will cause the evolution of ammonia gas.
Explanation (300 words):
When ammonium nitrate (NH₄NO₃) is mixed with sodium hydroxide (NaOH) in an aqueous solution, a chemical reaction occurs that produces ammonia gas (NH₃), water (H₂O), and sodium nitrate (NaNO₃).
The balanced chemical equation is:
NH₄NO₃ (aq) + NaOH (aq) → NH₃ (g) + H₂O (l) + NaNO₃ (aq)
Ammonium nitrate provides NH₄⁺ ions, while sodium hydroxide provides OH⁻ ions. The hydroxide ions deprotonate the ammonium ions, releasing ammonia gas (NH₃) and forming water. The remaining ions, Na⁺ and NO₃⁻, stay dissolved in the solution as sodium nitrate.
This reaction is a typical acid-base reaction, where NH₄⁺ acts as a weak acid and OH⁻ as a strong base. The evolution of a gas (ammonia) is an observable sign of the reaction. The ammonia gas has a sharp, pungent smell, which can be used to identify the gas. If the test is done near moist red litmus paper, the paper will turn blue, confirming the basic nature of the gas.
Unlike other combinations in the list (which may produce bubbles from CO₂ or precipitates from insoluble salts), this reaction’s key observation is ammonia gas release, not bubbling from carbonate or a visible solid. The lack of a visible precipitate or bubbling may make it less obvious, but the distinct smell of ammonia makes this reaction noticeable.
Therefore, when ammonium nitrate and sodium hydroxide are mixed in solution, the evolution of ammonia gas is the primary observable change due to a displacement reaction involving a weak acid and a strong base.