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解答化学计算题的分析过程,一般是通过反应物或生成物来求得。可见,一个题目往往可能有多种不同的解法,运用一题多解可以开拓思维,提高解题能力。 例 通氢气于32克氧化铜中,加热到残留物只有26克为止。问参加反起的氧化铜的百分率是多少? 分析:对这个问题学生往往(1)把26克全部视为Cu,(2)把32克CuO理解为全部参加反应,造成错误。其实,只要仔细分析“参加反应的氧化铜的百分率”这一句话,就不难看出只有一部分CuO参加反应,所以26克残留物中既有生成的Cu,也有没参加反应的CuO。因此,解题时可设未知数为:
The analytical process for answering chemical calculation questions is generally obtained through reactants or products. Obviously, a topic may have many different solutions. Using multiple solutions to one question can open up the mind and increase the ability to solve problems. For example, hydrogen is added to 32 g of copper oxide and heated to a residue of only 26 g. Q: What is the percentage of copper oxide involved in the reaction? Analysis: For this problem, students often (1) consider all 26 grams as Cu, and (2) understand 32 grams of CuO as all participating in the reaction, causing errors. In fact, as long as we carefully analyze the phrase “percentage of copper oxide that participates in the reaction,” it is not difficult to see that only a part of CuO participates in the reaction. Therefore, 26 grams of the residue contain both generated Cu and non-reacted CuO. Therefore, you can set the unknown when solving a problem: