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JEE Main 202524 JanuaryEvening Shift
Exam
JEE Main
Year
2025
Date
24 January
Shift
Evening Shift
Subject
Chemistry
Chapter
d and f Block Elements

JEE Main 2025 · 24 January · Evening Shift · Chemistry · d and f Block Elements

Find the compound ' A ' from the following reaction sequences. A...

Find the compound ' A ' from the following reaction sequences. A→ aqua-regia B→ (2) AcOH (1) KNO2∣NH4OH\mathrm{A} \xrightarrow{\text{ aqua-regia }} \mathrm{B} \xrightarrow[\text{ (2) } \mathrm{AcOH}]{\text{ (1) } \mathrm{KNO}_2 \mid \mathrm{NH}_4 \mathrm{OH}} yellow ppt \text{ yellow ppt }

Options

  1. ACoS
  2. BZnS
  3. CNiS
  4. DMnS

Correct answer

A. CoS

Step-by-step solution

Compound (A)(A) in the given reaction sequence is likely to be CoS. CoS+HNO3+3HCl→Co2++S↓+NOCl↑+2Cl−+2H2O\begin{aligned} \mathrm{CoS}+\mathrm{HNO}_3+3 \mathrm{HCl} \rightarrow \mathrm{Co}^{2+} & +\mathrm{S} \downarrow+\mathrm{NOCl} \uparrow \\ & +2 \mathrm{Cl}^{-}+2 \mathrm{H}_2 \mathrm{O}\end{aligned} The above solution is neutralised with NH4OH\mathrm{NH}_4 \mathrm{OH}. To a neutral solution of Co2+\mathrm{Co}^{2+}, acetic acid and saturated solution of KNO2\mathrm{KNO}_2 are added which results in the formation of yellow precipitate of K3[Co(NO2)6]Co2++7NO2−+2H++3 K+→K3[Co(NO2)6]+NO↑+H2O\mathrm{K}_3\left[\mathrm{Co}\left(\mathrm{NO}_2\right)_6\right] \mathrm{Co}^{2+}+7 \mathrm{NO}_2^{-}+2 \mathrm{H}^{+}+3 \mathrm{~K}^{+} \rightarrow \mathrm{K}_3\left[\mathrm{Co}\left(\mathrm{NO}_2\right)_6\right]+\mathrm{NO} \uparrow+\mathrm{H}_2 \mathrm{O}
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