Question

On passing excess of ammonia, Nessler's reagent solution changes its colour to _______.

• A. reddish brown
• B. blue
• C. greenish yellow
• D. pale red

Answer 1

The correct option is A reddish brown

Nessler's reagent $K_2\left[Hg{I}_4\right]$ when dropped into solvated ammonia results in the formation of a reddish brown precipitate known as 'Iodide of Millon's Base' and has a chemical formula $H_{2}NHgOHgI$. This reaction can be represented as:

$2K_2\left[Hg{I}_4\right]\left(aq\right)+N{H}_{4}OH\left(aq\right)+3KOH\left(aq\right)\to H_{2}NHgOHgI\left(s\right)+7KI\left(aq\right)+3H_{2}O\left(l\right)$