On addition of conc. $H_2SO_4$ to a chloride salt, colourless fumes are evolved but in the case of iodide salt, violet fumes come out. This is because.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → HI gets oxidized to $I_2$.
When concentrated (H_2SO_4\) is added to a chloride salt (like NaCl), it reacts to release HCl gas, which is colorless. However, when concentrated H₂SO₄ is added to an iodide salt (like NaI), violet fumes of I₂ are evolved.
Reason:
HI (hydrogen iodide) is a stronger reducing agent than HCl (hydrogen chloride).
H₂SO₄ is a strong oxidizing agent, and it oxidizes HI to I₂ (iodine), which is violet in color. The chemical reaction is:
\(2HI + H_2SO_4 \longrightarrow I_2 (violet fumes) + SO_2 + 2H_2O\)
This reaction occurs because HI can be easily oxidized to I₂, unlike HCl, which does not undergo oxidation under the same conditions
Other Options:
HI is of violet color: This is incorrect. HI is colorless; it is the iodine (I₂) produced from the oxidation of HI that is violet.
H₂SO₄ reduces HI to I₂: This is incorrect terminology. H₂SO₄ oxidizes HI to I₂, not reduces it.
HI changes to HIO₃: This is incorrect. The product of the reaction is iodine gas (I₂), not HIO₃ (iodic acid).
Thus, the correct answer is that HI gets oxidized to I₂, producing the violet fumes.