Potassium tetraiodomercurate(II)
Potassium tetraiodomercurate is an inorganic compound with the chemical formula. It consists of potassium cations and tetraiodomercurate anions. It is the active agent in Nessler's reagent, used for detection of ammonia.
Preparation
The compound crystallizes from a heated solution of mercuric iodide, potassium iodide, and precisely 2% water in acetone. Attempted synthesis in concentrated aqueous solution will give the pale orange monohydrate instead.Applications
is a precursor to analogous copper and silver salts .Nessler's reagent
Nessler's reagent, named after Julius Neßler, is a 0.09 mol/L solution of potassium tetraiodomercurate in 2.5 mol/L potassium hydroxide. This pale solution becomes deeper yellow in the presence of ammonia. At higher concentrations, a brown precipitate derivative of Millon's base may form. The sensitivity as a spot test is about 0.3 μg [Ammonia|] in 2 μL.The brown precipitate is not fully characterized and may vary from to.