Test Index

Salt Analysis

Section: Chemistry

Question : 15 of 38

Marks: +1, -0

A \xrightarrow{\;\text{ aqua-regia }\;} B \xrightarrow[\;\text{ (2) }\; \mathrm{AcOH}]{\;\text{ (1) }\; \mathrm{KNO}_2 [ \mathrm{NH}_4 \mathrm{OH} ] }

Solution:

Compound (A) in the given reaction sequence is likely to be CoS.

\mathrm{CoS} + \mathrm{HNO}_3 + 3 \mathrm{HCl} \longrightarrow \mathrm{Co}^{2+} \; + \mathrm{S} \downarrow + \mathrm{NOCl} \uparrow

\; + 2 \mathrm{Cl}^{-} + 2 \mathrm{H}_2\mathrm{O}

The above solution is neutralised with

\mathrm{NH}_4 \mathrm{OH}

To a neutral solution of

\mathrm{Co}^{2+}

, acetic acid and saturated solution of

\mathrm{KNO}_2

are added which results in the formation of yellow precipitate of

\mathrm{K}_3 [ \mathrm{Co} ( \mathrm{NO}_2 )_6 ]

\mathrm{Co}^{2+} + 7 \mathrm{NO}_2^{-} + 2 \mathrm{H}^{+} + 3 \mathrm{K}^{+} \longrightarrow \mathrm{K}_3 [ \mathrm{Co} ( \mathrm{NO}_2 )_6 ] + \mathrm{NO} \uparrow + \mathrm{H}_2\mathrm{O}

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