SIMPLE DEMONSTRATION OF CATALYSIS HERMAN KAMMIN Grover ~ievelandHigh School, New York City
NO CHEMISTRY instructor can deny that a study of the phenomenon of catalysis is of vital importance in chemistry. In fact, catalysis is discussed from the start in many introductory high-school courses in conjunction with the decomposition of potassium chlorate in the preparation of oxygen. It seems that the tendency, however, is to be dogmatic, and probably unscientific, in introducing this vital topic. The instructor can draw very little from the pupils' past scientific knowledge to which to appeal. *In many cases the pupils are merely told that mangaaese dioxide acts as a catalytic agent in the decomposition of potassium chlorate. Occasionally, an instructor shows that the decomposition proceeds faster with the catalyst hut rarely does he show that the catalyst undergoes no change. Perhaps the diacnlty involved, and what may seem the waste of valuable time, may deter the average instructor from a full presentation of this basically important chemical concept. To he more brief, it seems that no worthwhile proof accompanies the oxygen experiment. However, that is not important, as long as the phenomenon of catalysis can he demonstrated A simple demonstration on catalysis can he performed with a fair degree of success by the use of hydrogen peroxide and manganese dioxide. To show that manganese dioxide causes the hydrogen peroxide to decompose is simply a matter of mixing the two in a testtube and testing the resulting gas with a glowing splint. No heat is required. To show that the manganese dioxide does not undergo any change in the reaction,
it is best to weigh out a small quantity, about five grams at least, on a piece of.filter paper. A very sensitive balance is not necessaty as no calculations will have to be made. It is simply a question as to whether the manganese dioxide has lost weight or not. Of course, the more manganese dioxide used, the less the chance of experimental error. The manganese dioxide is then placed in a thoroughly.cleansed evaporating dish or beaker, hut the filter paper, tvith its last traces of the black powder, is saved for future filtration and weighing. A small quantity of hydrogen peroxide is then added to the manganese dioxide in the dish. If the instructor wishes he can again show that the resulting bubbling is due to the evolution of oxygen. When the effwescence subsides, the resulting mixture of manga.nese dioxide and water is passed through the original piece of filter paper. Care, of course, must be taken not to lose any of the mixture. A wash bottle helps in removing the last traces of the mixture from the dish. Finally the filter paper and its contents are dried in the air or in a desiccator and re-weighed. To show that the manganese dioxide has undergone no change it is best to save it for future use. The advantages claimed for this experiment are as follows: 1. Its simplicity. The steps consist merely of weighing, filtering, drying, and re-weighing. No complicated set-ups or heating are necessary. 2. Its proof. A catalyst not only hastens a chemical change, hut undergoes no change in weight and can he used over again.
