Experiment No. 5 Limit test for Arsenic
Limit test for Arsenic Principle: Limit test of Arsenic is based on the reaction of arsenic gas with hydrogen ion to form yellow stain on mercuric chloride paper in presence of reducing agents like potassium iodide. It is also called as Gutzeit test and requires special apparatus. Arsenic, present as arsenic acid in the sample is reduced to arsenious acid by reducing agents like potassium iodide, stannous acid, zinc, hydrochloric acid, etc. Arsenious acid is further reduced to arsine (gas) by hydrogen and reacts with mercuric chloride paper to give a yellow stain. H 3 AsO 4 + H 2 SnO 2 → H 3 AsO 3 + H 2 SnO 3 Arsenic acid Arsenious acid H 3 AsO 3 + 3H 2 → AsH 3 + 3H 2 O Arsenious acid Arsine The depth of yellow stain on mercuric chloride paper will depend upon the quality of arsenic present in the sample. Procedure: Test solution: The ...