1522
JOURNAL OF CHEMICAL EDUCATION
AUGUST,1931
AN EXPERIMENT ILLUSTRATING THE LAW OF MASS ACTION
Chloramine-T in aqueous solution is in a state of equilibrium represented by the following equations.
+
=
+
CHsCsH4S02NaNC1 H 2 0 CHsCsH4SOnNHa NaOCl NaOCl H.0 NaOH HOCl
+
=
+
(1)
(2)
Due to the formation of hypochlorite in its aqueous solution, chloramine-T liberates free iodine from a neutral solution of potassium iodide.
As a result the solution becomes strongly alkaline since the reactions represented by equations (1) and (2) progress toward the right as a consequence of the decomposition of hypochlorite. Since free iodine is soluble in the presence of excess hydroxyl ion, most of the iodine is left in solution.
If the concentration of hidroxyl ion could be repressed, most of the iodine would precipitate. This effect is accomplished by means of ammonium acetate which removes hydroxyl ion from the field of reaction due to the formation of ammonium hydroxide. The procedure for this experiment is as follows: Dissolve a small crystal of potassium iodide in 25 cc. of water. Add about ten drops of a 5% solution of chloramine-T. The solution will remain colorless or acquire a faint yellowish tinge. Now add several grams of ammonium acetate. The solution takes on a cherry color. This experiment illustrates the effect of removing or diminishing one of the reactants (hydroxyl ion) from a system in equilibrium. [See equation (4).I
