Nitrogen and its Compounds: Reactions of concentrated nitric (V) acid

4.0 Nitrogen and its Compounds

4.5.4 Reactions of concentrated nitric (V) acid

Watch the reactions of concentrated nitric (V) acid with sulphur, carbon, iron and phosphorus. Then answer Questions 4.5.4.

Questions 4.5.4

Complete equations 1 to 6 below.

1. S(s) + HNO₃(aq) → --- (aq) + --- + NO₂(g)
2. C(s) + HNO₃(aq) →
3. Fe(s) + HNO₃(aq) →
4. P(s) + HNO₃(aq) →
5. NH₃(g) + HNO₃(aq) →
6. HNO₃(aq) Heat→
7. Explain why, although concentrated nitric acid is colourless, it rapidly turns yellow on standing, as shown in the photograph that follows.




Figure 4.5.4: Colouration of nitric (V) acid



8. Suggest how the yellow colouration can be removed.
9. Complete the following general word equations for the reactions between concentrated nitric (V) acid and elements.
   1. Metal + Concentrated nitric (V) acid
   2. Non-metal + Concentrated nitric (V) acid
10. The retort flask and all parts of the set-up used in the laboratory preparation of nitric (V) acid, including the stopper, are made of glass. Give a reason for this.

Concentrated nitric (V) acid reacts as a powerful oxidizer (not as an acid) as it is itself reduced to nitrogen (IV) oxide (NO₂).

Example: 3Cu(s) + 8HNO₃(aq) → 3Cu(NO₃)₂(aq) + 4H₂O(l) + 2NO₂(g)