Question

Ammonium ions are detected with:
A) Nessler's reagent
B) Borsch reagent
C) Tollen's reagent
D) Fehling's solution

Answer 1

Hint:Mainly, Reagents are used to detect, measure or make other substances. Ammonium ions can be identified in a solution by adding dilute sodium hydroxide solution and gently heating. If ammonium ions are present, they will be converted to ammonia gas. Ammonia has a characteristic choking smell. It also turns damp red litmus paper or damp universal indicator paper blue.

Complete answer:
The ammonium cation is a positively charged polyatomic ion with the chemical formula \[\left( {N{H^ + }_4} \right).\;\] It is formed by the protonation of ammonia \[(N{H_3}).\;\] In given all reagents, Nessler's reagent is widely used in determination of ammonium compounds.
Nessler's reagent: It is an alkaline solution of Potassium tetraiodomercurate (II) \[\left( {{K_2}\left[ {Hg{I_4}} \right]} \right).\] It is prepared by combining potassium iodide \[\left( {KI} \right)\] and mercuric chloride \[\left( {HgC{l_2}} \right).\] It is made slightly alkaline by adding \[KOH{\text{ }}\,or\,{\text{ }}NaOH\]. An alkaline pale solution of \[({K_2}Hg{I_4})\] becomes deeper yellow in the presence of ammonia. At higher concentrations, a brown precipitate may form. On being reacted with gaseous ammonia it produces brown fumes and on being passed through a solution of ammonia, it gives a dirty brown precipitate.
The reaction involved is:
\[\] \[2{K_2}[Hg{I_4}] + 3KOH + N{H_3} \to \left[ {OH{g_2}.N{H_2}} \right]I + 7KI + 2{H_2}O\]
\[\left[ {OH{g_2}.N{H_2}} \right]I^-\] (iodide of Millon's base), the product formed is brown in colour and is used in tests for ammonium ion. It is a qualitative test for ammonia. It is an insoluble/ brown ppt.

Therefore, option (A) is correct

Note:
1. Exposure to high concentrations of ammonia in air causes immediate burning of the nose, throat and respiratory tract. Inhalation of lower concentrations can cause coughing, and nose and throat irritation.
2. Anhydrous ammonia is a liquid when compressed or cooled. It is stored under pressure to prevent vaporization so a large volume can be available for use.