Which of the following is not given by $\mathrm{SO}_2$ ?

1. It converts acidified iodates to iodine.
2. It decolourises acidified $\mathrm{KMnO}_4$ solution.
3. It reacts with acidified potassium dichromate to form green coloured solution.
4. It reacts with green coloured ferrous sulphate to form yellowish brown ferric sulphate.

Solution

(i) $\mathrm{SO}_2$ (Sulphur dioxide) reacts with potassium iodate to form sulphuric acid, potassium sulphate and iodine gas. $ 5 \mathrm{SO}_2+2 \mathrm{KIO}_3+4 \mathrm{H}_2 \mathrm{O} \longrightarrow 4 \mathrm{H}_2 \mathrm{SO}_4+\mathrm{K}_2 \mathrm{SO}_4+\mathrm{I}_2 $ (ii) $5 \mathrm{SO}_2+2 \mathrm{KMnO}_4+2 \mathrm{H}_2 \mathrm{O} \longrightarrow$ $ \mathrm{K}_2 \mathrm{SO}_4+2 \mathrm{H}_2 \mathrm{SO}_4+2 \mathrm{MnSO}_4 $ $\mathrm{SO}_2$ decolourise $\mathrm{KMnO}_4$ by converting it to $\mathrm{Mn}^{2+}$
(iv) $\mathrm{SO}_2$ reduces ferric salts into ferrous salt changing colour from yellow to light green. $ \underset{\text { Yellow }}{\mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3}+\mathrm{SO}_2+2 \mathrm{H}_2 \mathrm{O} \longrightarrow \underset{\text { Green }}{2 \mathrm{FeSO}_4}+2 \mathrm{H}_2 \mathrm{SO}_4 $

Asked in: AP EAMCET 2021 (24 Aug Shift 1)

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