Question

Give appropriate Re reasons for each of the following:-
Addition of chlorine to potassium iodide solution gives it a brown colour but excess of chlorine makes it colourless

Answer 1

$C{l}_2$ is a stronger oxidising agent than $I_2$, KI oxidises to $I_2$ which imparts brown colour to the solution.

$2KI\left(aq\right)+C{l}_2\left(g\right)\to 2KCl\left(aq\right)+I_2$(brown color)

but excess of chlorine , the I₂ so formed gets further oxidised to HIO₃ (colourless)

$5C{l}_2\left(g\right)+I_2+6H_{2}O\to 10HCl+2HI{O}_3$ (colorless)

Hence, Addition of $C{l}_2$ to $KI$ solution gives it a brown colour but excess of chlorine turns into colourless