question_answer

Nesslefs reagent is used to detect

A)  \[P{{O}_{4}}^{3-}\]                        

B)  \[MN{{O}_{4}}^{-}\]

C)  \[N{{H}_{4}}^{+}\]                         

D)  \[Cr{{O}_{4}}^{2-}\]

Correct Answer: C

Solution :

                 Nesslers reagent is prepared by the reaction of mercuric chloride in the excess of KI. \[HgC{{l}_{2}}+2KI\xrightarrow{{}}\underset{scarlet\text{ }ppt.}{\mathop{Hg{{l}_{2}}}}\,\,\,+2KCl\] \[Hg{{I}_{2}}+2KI\xrightarrow{{}}\underset{\begin{smallmatrix}  potassium\text{ }tetraiodo \\  mercurate\left( II \right)  \\  colourless\text{ }complex \end{smallmatrix}}{\mathop{{{K}_{2}}[Hg{{I}_{4}}]}}\,\] Alkaline solution of \[{{K}_{2}}\,[Hg{{I}_{4}}]\] is called Nesslers reagent. It is used to test \[N{{H}_{3}}\] or \[NH_{4}^{+}\] ions which give brown precipitate or colouration with ammonia due to the formation of the iodide of Millons base\[H{{g}_{2}}NI.{{H}_{2}}O\]. It has the structure                 (brown ppt.)