JEE Advanced 2016 · Paper 2 · Chemistry Q21

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ChemistrySingle correct+3 / -1Question 21 of 54

In the following reaction sequence in aqueous solution, the species X, Y and Z, respectively, are
$\ce{S2O3^{2-}}\xrightarrow{\ce{Ag+}}\underset{\text{clear solution}}{\mathbf X}\xrightarrow{\ce{Ag+}}\underset{\text{white precipitate}}{\mathbf Y}\xrightarrow{\text{with time}}\underset{\text{black precipitate}}{\mathbf Z}$

\ce{[Ag(S2O3)2]^{3-}}

\ce{Ag2S2O3}

\ce{Ag2S}

\ce{[Ag(S2O3)3]^{5-}}

\ce{Ag2SO3}

\ce{Ag2S}

\ce{[Ag(SO3)2]^{3-}}

\ce{Ag2S2O3}

, Ag

\ce{[Ag(SO3)3]^{3-}}

\ce{Ag2SO4}

, Ag

Answer and worked solution

Official answer: A

X. Ag⁺ added to excess thiosulphate dissolves as the complex $\ce{[Ag(S2O3)2]^{3-}}$ , a clear solution.

Y. With more Ag⁺, white $\ce{Ag2S2O3}$ precipitates.

Z. On standing, it hydrolyses to black $\ce{Ag2S}$ :
$\ce{Ag2S2O3 + H2O -> Ag2S + H2SO4}.$

(A)

Topics:Anion analysis Stability and applications

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JEE Advanced 2016 · Paper 2, Chemistry question 21