Q5 / 69 · JEE Advanced 2008 (Paper 1) · Chemistry
$$
\text { Aqueous solution of } \mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3 \text { on reaction with } \mathrm{Cl}_2 \text { gives }
$$
- A$\mathrm{Na}_2 \mathrm{~S}_4 \mathrm{O}_6$
- Correct answerB$\mathrm{NaHSO}_4$
- C$\mathrm{NaCl}$
- D$\mathrm{NaOH}$
Solution
Sodium thiosulphate, $\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3$ gets oxidised by chlorine water.
$$
\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3+4 \mathrm{Cl}_2+5 \mathrm{H}_2 \mathrm{O} \longrightarrow 2 \mathrm{NaHSO}_4+8 \mathrm{HCl}
$$
$\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3$ gets oxidised by $\mathrm{FeCl}_3$ into $\mathrm{Na}_2 \mathrm{~S}_4 \mathrm{O}_6$
$$
2 \mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3+2 \mathrm{FeCl}_3 \longrightarrow \mathrm{Na}_2 \mathrm{~S}_4 \mathrm{O}_6+2 \mathrm{FeCl}_2+2 \mathrm{NaCl}
$$
Further, $\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3$ decomposes on treatment with dilute acids
$$
\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3+2 \mathrm{HCl} \longrightarrow 2 \mathrm{NaCl}+\mathrm{SO}_2+\mathrm{S}+\mathrm{H}_2 \mathrm{O}
$$
Hence, the correct answer is option: 'B'.