Question

The colour of the precipitate formed when Cobalt ($II$) solution reacts with $K{NO}_2$ in acetic acid medium is:

• A. Pale Blue.
• B. Yellow.
• C. Green.
• D. Reddish Brown.

Answer 1

Answer: (B)

Yellow.

$K{NO}_2+{CH}_{3}COOH\to {CH}_{3}COOK+H{NO}_{2}Co{Cl}_2+2K{NO}_2\to Co{\left({NO}_2\right)}_2+2KClCo{\left({NO}_2\right)}_2+2H{NO}_2\to Co{\left({NO}_2\right)}_3+NO+H_{2}OCo{\left({NO}_2\right)}_3+3K{NO}_2+K_3\left[Co{\left({NO}_2\right)}_6\right]$

$K_3\left[Co{\left({NO}_2\right)}_6\right]$ Potassium cobaltinitrite, IUPAC name potassium hexanitritocobaltate(III),The compound finds some use as a yellow pigment.