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初中化学要求在课堂上使用托盘天平对比称量250毫升空气与250毫升二氧化碳,让学生观察天平指针的偏转,从而得出“二氧化碳是一种比空气重的气体……”的结论。事实上因250毫升二氧化碳的质量约是 0.49克,250毫升空气的质量约是0.32克,差值仅为0.17克。托盘天平只能称到0.1克,因而对0.17克的微小质量差,很难比较出来。为了提高实验效果,我自制一个简易天平,进行上述实验,效果非常明显。 仪器结构,如图所示。它分三部分:一根竹签,二个塑料袋,一个支撑物(铁架台,也可以在墙上钉一个长钉,或在晒衣服绳上吊一细线)。将两个塑料袋一正一倒挂在
Junior high school chemistry requires the use of a tray balance in the classroom to weigh 250 milliliters of air and 250 milliliters of carbon dioxide, allowing students to observe the deflection of the balance hands, and conclude that “carbon dioxide is a gas heavier than air...”. In fact, because the mass of 250 ml of carbon dioxide is about 0.49 g, the mass of 250 ml of air is about 0.32 g, and the difference is only 0.17 g. The balance of the tray can only weigh 0.1g, so it is difficult to compare the tiny difference of 0.17g. In order to improve the experimental results, I made a simple balance and performed the above experiment. The effect was very obvious. Instrument structure, as shown. It is divided into three parts: a bamboo stick, two plastic bags, a support (iron frame, you can also nail a nail on the wall, or hang a thin line on the clothesline). Put two plastic bags upside down