James M. Gaidis Contributed by Eugene G. Rochow Harvard College Cambridge, Mossochusetts
The Catalyzed Decomposition of Potassium Chlorate
Since the turn of the century, fewer thau a half-dozen articles have been published on the thermal decomposition of chlorates or perchlorates, and there have been none since Tian and Svilarich ( 1 ) examined the catalyzed decomposition of perchlorates in 1930.' Otto and 1:ry (2, 3) first showed that the thermal decomposition of potassium perchlorate catalyzed by l:e203 was unimolecular. A year later, they found that the no11-catalyzed decomposition of potassium chlorate also was unimolecular (at least approximately), when decomposing thus: To adjust for the disproportionation 4KCIOJ
-
3KC10r
+ KC1
and the concomitant decomposition KCIOi
KC1
+ 201
they introduced elaborate corrections, but in half of their trials, these last two reactions consumed 85% of the original chlorate, leaving only a small fraction to undergo the reaction as first written. The most
'After this paper was submitted, a note on the nature of the perchlorate decomposition was submitted by 0. Bostrup, K. Demandt, and K. 0. Hansen as one of the Textbook Errors of Turn JOIJRNAL and appenred 39,573 (1062). CONTRIBUTOR'S NOTE: I t is a time-honored custom in many collcges to allow undergraduates of marked research ability to pursue their own interests quite outside of (and in addition t o ) the regular course curriculum. Traditionally, some professor spots a st.udent of execptional ability and encourages him by providing laboratory space, supwvision, tutelage, unlimited discussion, access to books, or whatever else the student nteds to develop his scholarly bent. Sometimes an able student who is too quiet or self-effacing to make any claim to such personal attention, or even to be noticed, will simply find i t impossible to keep away from the graduate research laboratories, and will eventually be taken in as a n informal apprentice. This is in the tradition of the ancient European university, a tradition transplanted t o our country long ago. Many of our outstanding chemists went through such an experience, and for them i t made all the difference between remaining an ordinary student :md becoming an exceptionally inquisitive scholar. By its very nature, such encouragement of undergraduate rosearch (especially among freshmen and sophomores) cannot he organized or evaluated on a competitive basis. It remains a personal relationship which depends upon personal interests and personal characteristics: i t has nothing to do with credits or with coverage of a subject. Nevertheless, it does take a great deal of a proiessor'rr time (no matter how gladly given), and i t does compete with d l theworthycourses in the student's schedule. As today's curricula become more crowded, there is danger that such independent and informal study might be squeezed out, to the great loss of future scholarship. In order to encourage the practice of early individual study without interfering with its personal and informal nature, the
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Journal of Chemical Education
elaborate corrections could hardly he expected to remove all the error involved. I n 1820 Dohereiner first used mauganese dioxide as a catalyst for the chlorate decomposition, and shortly afterward it was realized that its use was accompanied by the evolution of minute quantities of a strongly-oxidizing gas along with the oxygen. Oxides more acidic than manganese dioxide gave larger quantities of the strongly-oxidizing gas. In 1855 C. F. Schonbein claimed that. the gas is ozone, as did Brunk (4) in 189'3, but Leeds (j),McLeod (6),and Sodeau (7) all have claimed that the gas is chlorine. The present study was undertaken because the author had not found in his textbooks any adequate explanation of how or why manganese dioxide acts as a catalyst in the decomposition of potassium chlorate. Moreover, almost everyone who has used the reaction has ignored the presence and the nature of the stronglyoxidizing gas. I n view of the uses to which oxygen from potassium chlorate is put, such an impurity would not he negligible. Most previous workers have used 10 to 20y0 of catalyst, but preliminary experiments in the present work showed considerable advantage in using only 0 2 % of Mn02. With this limited amount of catalyst the temperature may be increased enough to fuse the potassium chlorate, resulting in a homogeneous faculty of Harvard College began three years ago to grant up to one-fourth of the first-year's credit for "ungraded independent study." The practice has been limited to those students xhn, in the opinion of the Office of Advanced Standing and a professor who has agreed to direct the work, would advance faster toward intellect?lal maturity in this way than by staying within the regular course framework. The permission does not carry with it waiver of any required courses or subjects: it simply moves a research elective down into the freshman (and inevitahlv the sophomore) year for those who are well enough prepared or sufiieientlv eifted to benefit from it. As for the "indcnendcnt
freshman and sophomore research reports I have rec~ived during the past three years, most of which, I believe, contain significant research results. This particular report is presented ( I ) as an example of what can come out of underclass research, quite apart from any benefit to the student, and (2) because the subject ia ot interest to many tcachers of secondary-school and college chemistry. It represents part of two year's w r k on the part of Mr. Geidis, for which he received one semester-course credit under the program. The project was not assigned, but (as usual) was the student's own choice. All the equipment was designed and built by Mr. Gaidis, and he alone drew the conclusions, wrote the paper, and drew the diagrams. I have rearranged the order, the references, and the diagrams to comply hut have not altered with t,he editorial practices D ~ T I I I SJOURXAL, his thoughts. EUGENEG. ROCHOW
colored liquid, yet without causing an excessive rate of oxygen evolution. Liquid-phase reactions, of course, offer the advantage of greater reproducibility in kinetic measurements. Some conclusions could also be drawn from the color of the liquid. (Only four writers previously have described a purple melt, for example. For the rest the color was hidden, nndoubt,edly by an excessive amount of catalyst.) Kinetic measurements were made a t different temperatures, and the evolved gases were examined. Experiments Performed
The apparatus was not complicated. Known mixtures of I
