Answer to Question #310686 in General Chemistry for kyjam

Question

How to perform a potency test or concentration test of iodine (i2) on a 1L lugol's solution of iodine.

Answer 1

Lugol's solution is an aqueous solution which contains iodine (I₂) and potassium iodide (KI) in a ratio of 1:2.

Lugol's iodine solution is used for Gram staining and can be used as an antiseptic and disinfectant for emergency disinfection of drinking water, and as a reagent for starch detection in routine laboratory and other medical tests.

In the standard Gram procedure the aniline dyes in the cell tissue of microorganisms form a red dye-iodine complex when exposed to iodine. In Gram-positive microorganisms the dye-iodine complex cannot subsequently be dissolved from the cells by decolorizing agents such as alcohol or acetone. The cells remain dark blue in color. In Gram-negative microorganisms the dye-iodine complex is dissolved and the cell turns red as a result of counterstaining.