How does copper react with the following? Give balanced equations:(i) Dilute nitric acid.(ii) Concentrated nitric acid.

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Points to Remember:

  • Copper’s reactivity with nitric acid depends on the concentration of the acid.
  • Different products are formed depending on the concentration of nitric acid.
  • Balanced chemical equations must be provided for each reaction.

Introduction:

Copper (Cu), a transition metal, exhibits variable oxidation states, making its reactions with acids complex. Nitric acid (HNO₃) is a strong oxidizing agent, and its reaction with copper produces different products depending on its concentration. Dilute nitric acid acts as a typical acid, while concentrated nitric acid acts as an oxidizing agent, leading to different reaction pathways. Understanding these reactions is crucial in various chemical processes and industrial applications.

Body:

(i) Reaction of Copper with Dilute Nitric Acid:

  • Mechanism: In dilute nitric acid, copper is oxidized to copper(II) ions (Cu²⁺), while nitric acid is reduced to nitrogen monoxide (NO), a colorless gas that quickly turns brown in air due to oxidation to nitrogen dioxide (NO₂). The reaction is relatively slow.

  • Balanced Equation:

3Cu(s) + 8HNO₃(aq) → 3Cu(NO₃)₂(aq) + 2NO(g) + 4H₂O(l)

(ii) Reaction of Copper with Concentrated Nitric Acid:

  • Mechanism: Concentrated nitric acid is a stronger oxidizing agent than dilute nitric acid. Copper is still oxidized to copper(II) ions, but nitric acid is reduced to nitrogen dioxide (NO₂), a brown, toxic gas. The reaction is vigorous and exothermic.

  • Balanced Equation:

Cu(s) + 4HNO₃(conc.) → Cu(NO₃)₂(aq) + 2NO₂(g) + 2H₂O(l)

Comparison Table:

| Feature | Dilute Nitric Acid | Concentrated Nitric Acid |
|—————–|—————————————————|—————————————————-|
| Oxidizing Agent | HNO₃ (weaker oxidizing agent) | HNO₃ (stronger oxidizing agent) |
| Copper Product | Cu(NO₃)₂ (Copper(II) nitrate) | Cu(NO₃)₂ (Copper(II) nitrate) |
| Nitric Acid Product | NO (Nitrogen monoxide) – turns brown in air as NO₂ | NO₂ (Nitrogen dioxide) |
| Reaction Rate | Relatively slow | Vigorous and exothermic |
| Gas Produced | Colorless NO (turns brown) | Brown NO₂ |

Conclusion:

Copper reacts differently with dilute and concentrated nitric acid due to the varying oxidizing power of the acid. Dilute nitric acid produces nitrogen monoxide (NO), while concentrated nitric acid produces nitrogen dioxide (NO₂). Both reactions yield copper(II) nitrate. Understanding these reactions is essential in various chemical applications, including the purification of copper and the synthesis of copper compounds. Further research into optimizing reaction conditions for specific applications, such as minimizing the production of harmful nitrogen oxides, is crucial for environmental sustainability and industrial safety. The balanced equations provided offer a clear representation of the stoichiometry involved in these important chemical reactions.

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