Why does sodium iodide react with concentrated sulfuric acid to give purple fumes and H₂S, unlike sodium chloride?

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Question

Why does sodium iodide react with concentrated sulfuric acid to give purple fumes and H₂S, unlike sodium chloride?

Accepted Answer

Iodide is a strong enough reducing agent to reduce H₂SO₄, and is oxidised to I₂ — Award 1 mark. HI forms first, but iodide reduces sulfur from +6 as far as −2 (H₂S), and is itself oxidised to iodine, seen as purple vapour.

Answer

Sulfuric acid is reduced only by chloride ions

Answer

Sodium iodide decomposes on its own when warmed

Answer

Iodide ions oxidise the sulfur in sulfuric acid to +8

Answer

Iodide is a strong enough reducing agent to reduce H₂SO₄, and is oxidised to I₂

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