Nitrogen and its Compounds: Nitrogen (IV) oxide

4.0 Nitrogen and its Compounds

4.3.3 Nitrogen (IV) oxide

Nitrogen (IV) oxide is prepared by reacting copper metal with concentrated nitric (V) acid.

Figure 4.3.3(a): Laboratory preparation of nitrogen (IV) oxide

Questions 4.3.3

1. Write the chemical formula of nitrogen (IV) oxide.
2. Write an equation for the reaction between concentrated nitric (V) acid and copper metal to produce nitrogen (IV) oxide (Hint: The other products are similar to those accompanying nitrogen (II) oxide).
3. How can nitrogen (IV) oxide gas be produced from copper metal and dilute nitric (V)? Hint: Air is required.)
   
   

   Figure 4.3.3(b): Illustrations of some properties of nitrogen (IV) oxide, NO₂

   
   
4. State any three physical properties of nitrogen (IV) oxide.
5. Identify any three chemical properties of nitrogen (IV) oxide.
6. Write equations for the reactions of nitrogen (IV) oxide with each of the following substances. (a) heated copper metal (b) heated magnesium metal (c) burning phosphorus (d) water
7. Explain (a) why nitrogen (IV) oxide cannot be collected over water (b) how nitrogen (IV) oxide can be dried and collected (c) how nitrogen (IV) gas can be condensed and collected.
8. Describe how you would chemically distinguish nitrogen (IV) oxide from nitrogen (II) oxide.
9. 2.12 g of copper metal was reacted with excess concentrated nitric (V) acid. Determine the volume at s.t.p of the nitrogen (IV) oxide produced (Cu = 63.5; molar gas at s.t.p is 22.4 dm³).

NB: Reactions of nitrogen oxides with hot and burning elements is due to the fact that heat energy, especially from elements that burn at high temperatures, decomposes nitrogen oxides into free oxygen and nitrogen. The free oxygen then combines with the elements to form oxides while nitrogen, being unreactive, is released in the uncombined elemental state.

NB: For the reaction between magnesium metal and oxides of nitrogen, magnesium nitride solid is produced alongside magnesium oxide. Accordingly, less nitrogen is collected.

Questions 4.3.4

Nitrogen (IV) oxide reacts with water to form nitric (III) acid (HNO₂) and nitric (V) acid (HNO₃).

1. Write a balanced chemical equation for the reaction.
2. In the presence of air, nitric (III) acid is oxidized to nitric (V) acid as the only product. Write an equation for this reaction.

NB: These reactions are used in the last steps of industrial manufacture of nitric (V) acid.