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在九年义务教育课程标准教材《化学》和以前各种版本的初中化学教材中都列有一个典型的“二氧化碳熄灭蜡烛火焰”的实验。用于说明二氧化碳不支持燃烧,而且它的密度比空气大,所以在大烧杯内,下层的蜡烛火焰先熄灭,上层的火焰后熄灭,如图1所示。有的中学老师为了培养学生的创新思维,重新设计了一个倒置的烧杯实验,结果发现蜡烛火焰从上至下依次熄灭。从而得出结论:在倒置的烧杯中,由于蜡烛燃烧产生的二氧化碳是热的,其密度减小,使二氧化碳气流上升,并且从上至下逐渐充满烧杯,致使蜡烛火焰从上至下依次熄灭。这个实验及其结论流传很广,在学生中考练习题
In the nine-year compulsory education curriculum standard textbook “Chemistry” and the previous versions of junior high school chemistry textbook, there is a typical “carbon dioxide extinguished candle flame” experiment. Used to illustrate that carbon dioxide does not support combustion, and its density is greater than that of air. Therefore, in the large beaker, the flame of the lower candle is extinguished first and the flame of the upper layer is extinguished, as shown in Figure 1. In order to cultivate students’ innovative thinking, some middle school teachers redesigned an inverted beaker experiment and found that the candle flame went out from top to bottom. It follows that in an inverted beaker, the carbon dioxide produced as a result of the burning of the candle is hot, its density decreases, the carbon dioxide flow rises, and the beaker is gradually filled from top to bottom, causing the candle flames to extinguish in turn from top to bottom. The experiment and its conclusions are widely circulated and students practice exams