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Difficulty: MediumAmmonia and Trioxonitrate(V) Acid Preparation and Reactions

In laboratory chemistry, specific procedures and chemical tests are used to identify and handle ammonia (NH3NH_3) and trioxonitrate(V) acid (HNO3HNO_3). Match each laboratory procedure on the left with its corresponding chemical observation or outcome on the right.

  • Exposing ammonia gas to concentrated hydrochloric acid vaporObservation of dense white fumes of ammonium chloride (NH4ClNH_4Cl)
  • Performing the brown ring test on a trioxonitrate(V) salt solution using iron(II) tetraoxosulfate(VI) and concentrated H2SO4H_2SO_4Formation of a brown ring of iron(II) nitrosyl complex at the liquid junction
  • Passing moist ammonia gas through a drying tower containing quicklime (CaOCaO)Efficient drying of the alkaline gas without chemical reaction
  • Reacting concentrated trioxonitrate(V) acid with copper turningsEvolution of reddish-brown gas, nitrogen(IV) oxide (NO2NO_2)

Answer

Matching pairs: (1) Exposing ammonia to HCl vapor matches Observation of dense white fumes of ammonium chloride. (2) Performing the brown ring test matches Formation of a brown ring of iron(II) nitrosyl complex. (3) Passing moist ammonia through quicklime matches Efficient drying of the alkaline gas without chemical reaction. (4) Reacting concentrated trioxonitrate(V) acid with copper matches Evolution of reddish-brown gas, nitrogen(IV) oxide.
Each procedure pairs directly with its established chemical outcome: ammonia gas reacts with hydrogen chloride vapor to yield dense white ammonium chloride fumes; the brown ring test relies on forming a brown iron(II) nitrosyl complex; quicklime (CaOCaO) safely dries basic ammonia without chemical reaction; and concentrated trioxonitrate(V) acid oxidizes copper to release reddish-brown nitrogen(IV) oxide gas.

Step-by-Step Solution

1
Analyze the gas-phase reaction of ammonia with hydrogen chloride vapor.
NH3(g)+HCl(g)→NH4Cl(s)NH_3(g) + HCl(g) \rightarrow NH_4Cl(s), producing dense white fumes.
Ammonia gas is alkaline and reacts with acidic hydrogen chloride gas to produce fine solid particles of ammonium chloride.
2
Identify the chemical process involved in the brown ring test for trioxonitrate(V) ions.
Iron(II) ions reduce trioxonitrate(V) to nitrogen(II) oxide (NONO), which then combines with excess Fe2+Fe^{2+} ions to yield [Fe(H2O)5NO]2+[Fe(H_2O)_5NO]^{2+}.
Concentrated H2SO4H_2SO_4 forms a dense bottom layer, creating a distinct interface where the brown nitrosyl complex accumulates.
3
Select the appropriate desiccant for ammonia gas.
Unslaked lime / quicklime (CaOCaO) dries ammonia effectively.
Acidic drying agents like H2SO4H_2SO_4 or P4O10P_4O_{10} react with NH3NH_3, while anhydrous CaCl2CaCl_2 forms an addition complex (CaCl2⋅8NH3CaCl_2 \cdot 8NH_3); therefore, basic CaOCaO must be used.
4
Examine the reaction between concentrated trioxonitrate(V) acid and copper metal.
Cu(s)+4HNO3(aq)→Cu(NO3)2(aq)+2NO2(g)+2H2O(l)Cu(s) + 4HNO_3(aq) \rightarrow Cu(NO_3)_2(aq) + 2NO_2(g) + 2H_2O(l), evolving nitrogen(IV) oxide gas.
Concentrated HNO3HNO_3 is a powerful oxidizing agent, yielding reddish-brown NO2NO_2 gas upon reaction with copper.

Key Concept

Laboratory Preparation, Identification, and Reactions of Ammonia and Trioxonitrate(V) Acid
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Topics

Ammonia and Trioxonitrate(V) Acid Preparation and Reactions

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