Question

On addition of conc.sulphuricacid to chloride salt, colourless fumes are evolved but in case of iodine salt,violet fumes come out.this is because

Answer 1

Answer on Question #44486 – Chemistry – Inorganic Chemistry

Question

On addition of concentrated sulphuric acid to chloride salt, colourless fumes are evolved but in case of iodine salt, violet fumes come out. This is because...

Answer

Concentrated sulphuric acid is a strong oxidant, and chlorine and iodine in oxidation state -1 entering into the composition of corresponding salts are reducers.

In case of chloride salt the red-ox reaction is as follows

$$\begin{array}{c c c c} - 1 & + 6 & 0 & + 4 \end{array}$$ $$2 \mathrm{NaCl} + 2 \mathrm{H_2SO_4} \longrightarrow \mathrm{Cl_2\uparrow} + \mathrm{SO_2\uparrow} + \mathrm{Na_2SO_4} + 2 \mathrm{H_2O}$$

Two gasses, namely $\mathrm{Cl_2}$ and $\mathrm{SO_4}$ are evolved as a result of the red-ox reaction. $\mathrm{SO_4}$ is colourless and $\mathrm{Cl_2}$ is pale green. That is why the fumes evolved looks colourless.

In case of iodine salt the red-ox reaction is as follows

$$\begin{array}{c c c c} - 1 & + 6 & 0 & + 4 \end{array}$$ $$2 \mathrm{NaI} + 2 \mathrm{H_2SO_4} \longrightarrow \mathrm{I_2\uparrow} + \mathrm{SO_2\uparrow} + \mathrm{Na_2SO_4} + 2 \mathrm{H_2O}$$

Under ambient conditions $\mathrm{I_2}$ is a solid, but at the elevated temperature it is a violet gas. In given reaction $\mathrm{I_2}$ is evolved as a violet gas. That is why the violet fumes come out.

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