In the brown ring test for the nitrate ion, the brown colour is due to

In the brown ring test for the nitrate ion, the brown colour is due to

Options

(a) [Fe(H₂O)₅NO]²⁺
(b) [Fe(H₂O)₅NO]³⁺
(c) [Fe(H₂O)₆]⁺
(d) [Fe(H₂O)₅NO₂]²⁺

Correct Answer:

[Fe(H₂O)₅NO]²⁺

Explanation:

When an aqueous solution of the nitrate salt is treated with freashly prepared solution of ferrous sulphate and concentrated H₂SO₄, a brown ring is formed on account of the formation of complex [Fe(H₂O)₅NO]SO₄ at the junction of two liquids. NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃. 6FeSO₄ + 2HNO₃ + 3H₂SO₄ → 3Fe₂(SO₄)₃ + 4H₂O + 2NO. [Fe(H₂O)₆]SO₄.H₂O + NO → [Fe(H₂O)₅NO]SO₄ + 2H₂O(brown ring).

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