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近几年来,化学讨论型计算题在各种选拔性考试中所占比例愈来愈大。本文就此类题目的特点与归类作一简单介绍。1 过量问题讨论 此类题目的特点是告诉一个化学反应中多种物质的量,以迷惑学生。解题时要认真分析题意,抓住“参加反应”的量或“反应生成”的量,开展讨论。 例1 现有氢、氧混合气体10克在一密闭钢质容器内点火爆炸,冷却后测得容器内有水9克。求原混合气体中氢气的质量分数。 解析:此题已知量有两个,显然代入化学方程式中计算的量是水的质量9克,而不是H_2质
In recent years, chemistry-discussed calculations have become more and more important in various selection tests. This article gives a brief introduction to the characteristics and classification of such topics. 1 Discussion of Excessive Questions The feature of such questions is to tell the amount of multiple substances in a chemical reaction to confuse students. To solve the problem, you must carefully analyze the meaning of the problem and seize the amount of “reactions” or “response generation” to discuss. Example 1 The existing hydrogen and oxygen mixed gas 10g ignited and exploded in a sealed steel container. After cooling, 9g of water was measured in the container. Find the mass fraction of hydrogen in the original gas mixture. Analysis: There are two known quantities for this problem. It is clear that the amount calculated in the chemical equation is 9 grams of water, not H2.