在初中化学课堂教学中,当演示某些气体的性质时,如演示氧气的化学性质,要做氧气分别与碳、硫、磷、铁、石蜡反应这5个演示实验,如果边制取氧气边进行实验,则会浪费许多时间。化学教师一般在课前事先制取氧气并收集在集气瓶中,瓶口加盖涂有凡 In junior high school chemistry class teaching, when demonstrating the nature of certain gases, such as demonstration of the chemical properties of oxygen, oxygen should be done with carbon, sulfur, phosphorus, iron, paraffin reaction of the five demonstration experiments, To experiment, you waste a lot of time. Chemistry teachers generally pre-class preparation of oxygen and collected in the gas collection bottle, bottle cap stamped with Van