Question

On addition of $conc.H_{2}S{O}_4$ to a chloride salt, colourless fumes are evolved but in case of iodide salt, violet fumes come out. This is because :

• A. $H_{2}S{O}_4$ reduces HI to $I_2$
• B. $HI$ is of violet colour
• C. $HI$ gets oxidised to $I_2$
• D. $HI$ changes to $HI{O}_3$

Answer 1

Answer: (C)

$HI$ gets oxidised to $I_2$

Hydrogen iodide is a stronger reducing agent than sulphuric acid so it reduces $H_{2}S{O}_4$ to $S{O}_2$ and $HI$ to $I_2$.

Chloride salts when treated with sulphuric acid to give colourless gas due to formation of $HCl$ gas.

$NaCl+H_{2}S{O}_4⟶HCl+{Na}_{2}S{O}_4$

Due to the formation of iodine (I_2) gas, the violet fumes are evolved during the reaction.

$2NaI+H_{2}S{O}_4\to N{a}_{2}S{O}_4+2HI\stackrel{H_{2}S{O}_4}{⟶}2H_{2}O+S{O}_2+I_2$

Hence, option $C$ is correct.