In the following sequence of reactions the correct P, Q and R are respectively in dil. AcOHP [thiourea]solid… · ABC26IN1143

Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Reaction Mechanisms Substitution · Exam: CSIR NET JUNE 2019 · Marks: 2 · Difficulty: Medium

In the following sequence of reactions the correct P, Q and R are respectively
\[ \begin{array}{l} \underset{\text{in dil. AcOH}}{\mathrm{P}} \xrightarrow[\text{thiourea}]{\text{solid}} \mathrm{N_2}\uparrow + \text{Solution} \xrightarrow[\text{soln.}]{\text{dil. }\mathrm{FeCl_3}} \mathrm{Q}\ \text{(blood red)} \\ \mathrm{Q} \xrightarrow[\text{soln.}]{\text{dil. }\mathrm{HgCl_2}} \mathrm{R}\ \text{(colourless)} \end{array} \]
(a)$\mathrm{KNO_2}$, $\mathrm{CO_2}$, $[\mathrm{Fe(H_2O)_5S}]^{+}$, $\mathrm{HgS}$
(b)$\mathrm{KNO_2}$, $\mathrm{N_2}$, $[\mathrm{Fe(H_2O)_5(SCN)}]^{2+}$, $[\mathrm{Hg(SCN)_4}]^{2-}$
(c)$\mathrm{KNO_3}$, $\mathrm{N_2}$, $[\mathrm{Fe(H_2O)_5(CN)}]^{2+}$, $[\mathrm{Hg(OCN)_4}]^{2-}$
(d)$\mathrm{NaN_3}$, $\mathrm{N_2}$, $[\mathrm{Fe(H_2O)_5(N_3)}]^{2+}$, $[\mathrm{Hg(N_3)_4}]^{2-}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Nitrite oxidises thiourea, giving N₂ gas and SCN⁻. FeCl₃ then forms the blood-red [Fe(H₂O)₅(SCN)]²⁺, which HgCl₂ converts to colourless [Hg(SCN)₄]²⁻. P = KNO₂ (b).

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