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THE STABILITY OF SOLUTIONS FOR THE IODINE CLOCK REACTION GEORGE 8. RAUPPMAN u d CHARLES R. HALL Fresno State College, Fresno, California
INORDER to avoid the instability which has prevented the advance preparation of large quantities of solutions for the "iodine clock" demonstration, Conway' proposed the addition of alcohol to the acidified sulfite solution in order t o inhibit oxidation. The present authors felt that the escape of volatile sulfur dioxide from acidified sulfite solutions might also contribute to instability. Therefore, it would seem desirable t o keep the sulfuric acid separate from the sulfite solution. To test this view, three series of solutions were prepared: (1) the two solutions suggested by Alyea2; (2) the same two solutions with the acid in the potassium iodate rather than in the sulfite solution; (3) three solutions, one containing potassium iodate, the second containing the acid, and the third containing starch and sodium CONWAY, W. J., J. CHEM.EDUC., 6, 398 (1940) ALYEA,H. N., J. CBEM.Eooc., 32.9 (1955).
VOLUME 35, NO. 10, NOVEMBER, 1958
acid sulfite. After standing for about one year in tightly closed containers, the first series of solutions required several seconds t o completely turn blue after the characteristic induction period had elapsed, while color changes for the second and t h i d series were still instantaneous. To simulate the further passage of time and t o facilitate the escape of sulfur dioxide, the three series of solutions were exposed t o the air in open beakers. After six hours, only the t h i d series of solutions still showed a sharp color change. After 24 hours, only the third solution showed any color change a t all. As for appearance, the starch solution of the first series had turned cloudy after one year, while the starch solutions of the second and t h i d series remained clear. Fungi (Phycmyces nilens) were found in the sulfuric acid solution of the third series, but were not detrimental t o the reaction.
