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极限是数学分析的基本概念之一,在化学解题中,常运用这个概念,假设所研究的问题无限接近于极端情况,以达到简化解决问题过程的目的。下面举例说明极限观点在分析、讨论和解答有关化学判断题中的应用。一、某种物质中是否含杂质的判断例1(’94全国高考题)把含有某一种氯化物杂质的MgCl_2粉末95mg溶于水后,与足量的AgNO_3溶液反应,生成AgCl沉淀300mg,则该MgCl_2中的杂质可能是()。(A)NaCl(B)AlCl_3(C)KCl(D)CaCl_2
The limit is one of the basic concepts of mathematical analysis. In chemical problem solving, this concept is often used. It is assumed that the problem studied is infinitely close to the extreme situation, so as to simplify the problem solving process. The following examples illustrate the application of the limit viewpoint in analyzing, discussing, and answering chemical judgment questions. I. Judgment 1 for the presence of impurities in a substance (’94 National Entrance Examination Question) After dissolving 95 mg of MgCl 2 powder containing a certain kind of chloride impurity in water, react with a sufficient amount of AgNO 3 solution to form 300 mg of AgCl precipitate. Then the impurity in MgCl 2 may be (). (A) NaCl(B)AlCl_3(C)KCl(D)CaCl_2