Question

How is $O_3$ estimated quantitatively?

Answer 1

When $O_3$ is treated with excess of $KI$ solution buffered with borate buffer $(pH=9.2)$

$I_2$ is liberated quantitatively, according to the following equation:

$2I_{\left(aq\right)}^{-}+H_2{O}_{\left(l\right)}+O_{3\left(g\right)}\to 2O{H}_{\left(aq\right)}^{-}+I_{2\left(s\right)}+O_{2\left(g\right)}$

The $I_2$ thus liberated is titrated against a standard solution of sodium thiosulphate using starch as an indicator.

$\underset{Sodiumthiosulphate}{2N{a}_2{S}_2{O}_3}+I_2\to \underset{SodiumTetrathionate}{N{a}_2{S}_4{O}_6}+2NaI$

Quantitative estimation of $O_3$ is thus carried out.