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Sodium Iodide

In the reaction of sodium iodide with sulfuric acid, the sulfuric acid acts as an acid and donates a proton to the halide.Misty fumes of HI are observed. NaI + H2SO4 → NaHSO4 + HI
A redox reaction also occurs:The iodide ions are strong enough reducing agents to reduce the concentrated sulphuric acid to sulfur dioxide, sulfur and hydrogen sulfide.The iodide ions are oxidised to iodine.Overall:2HI + H2SO4 → 2H2O + SO2 + I26HI + H2SO4 → 4H2O + S + 3I28HI + H2SO4 → 4H2O + H2S + 4I2You get a mixture of products: misty fumes of HI, colourless sulfur dioxide gas, yellow solid sulfur, hydrogen sulfide gas (smell of bad eggs) and iodine (a black solid or purple vapour).

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Specification: Edexcel Chemistry (8CH0), AS-level, Topic 4B: The elements of Group 7 (halogens). Topic: Group 7.

Key terms in this lesson

reducing agent
A substance that donates electrons to another species, causing it to be reduced, while it is itself oxidised.

More in Group 7

All 14 lessons in Group 7 · All Edexcel AS-level Chemistry topics