JUNE, 1951
A METHOD OF PREPARING OXYGEN F. T. GROVES Central High School, Piqua, Ohio
SEVERAL years ago I became dissatisfied with the usual method of preparing oxygen in the laboratory, that of heating a mixture of potassium chlorate and manganese dioxide. That there is some danger in performing this experiment is evident from the fact that there have been, in recent years several reports of injuries to students from explosions. I once had a student who mixed potassium chlorate and manganese dioxide, as directed, and also included sulfur and charcoal which was to be used in testing the gas produced. Fortunately the student was not injured by the resulting explosion. My principal objection t o the above method, however, is that few students can control the heating of the mixture in the test tube sufficiently well to avoid producing a white cloud in the collecting bottles. In spite of the fact that their observation of the air about them shows oxygen to be invisible and colorless some students identify the white cloud in the bottles as oxygen. For these reasons I have for several years used the method described below. The ordinary hydrogen generator is used. A teaspoonful of manganese dioxide is placed in the generator bottle with about 20 ml. of water and the bottle is rotated to mix the contents. Superoxol, 30 per cent hydrogen peroxide, is diluted to 6 per cent with water. The hydrogen peroxide is poured, as needed, into the
thistle tube. The reaction is easily controlled, and the gas produced is colorless. Unless a student is careless and allows much gas to escape when changing bottles, 50 ml. of the 6 per cent solution should easily produce four 250-ml. bottles of oxygen. The action of manganese dioxide as a catalyst is just as well demonstrated by this experiment as with the conventional method. I t is somewhat more expensive than the conventional method. The use of potassium chlorate and manganese dioxide is later demonstrated by the following method. Two tubes are clamped so that the bottoms of the two can he heated equally by a burner flame. One tube is supplied with a small quantity of potassium chlorate and the other tube with a mixture of the chlorate and manganese dioxide. Testing with a glowing splint shows which produces oxygen first. A tube of manganese dioxide alone is then heated and tested in a like manner to show that no oxygen can be obtained from that chemical by the heat of a Bunsen burner flame. The above demonstration serves also as an excellent project for an ambitious student. Ask the student to find out how many of the oxides found on the laboratory shelves will serve as a catalyst for the decomposition of potassium chlorate. The results mn.y surprise even the teacher.
