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Karl Telemann

What are the products formed when dilute nitric acid is electrolyzed using graphite electrodes?

Declan Hackett  Follow

When dilute nitric acid is electrolyzed, oxygen gas is formed at the anode and hydrogen gas is formed at the cathode.

The ionization of HNO₃ gives H⁺ and NO₃⁻ ions, while the ionization of water gives H⁺ and OH⁻ ions.

At the anode:
OH⁻ and NO₃⁻ ions migrate to the anode. OH⁻ ion is preferentially discharged to give O₂ gas because OH⁻ ion is lower than NO₃⁻ ion in the electrochemical series.
4OH⁻(aq) → 2H₂O(ℓ) + O₂(g) + 4e⁻
OR: 2H₂O(ℓ) → 4H⁺(aq) + O₂(g) + 4e⁻

At the cathode:
H⁺ ion migrates to the cathode. H⁺ ion is then discharged to give H₂ gas.
2H⁺(aq) + 2e⁻ → H₂(ℓ)
OR: 2H₂O(ℓ) + 2e⁻ → H₂(g) + 2OH⁻(aq)

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