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学会“解疑”的关键在于学会逻辑思维。在练习课中,组织学生讨论一些比较复杂的问题,从不同角度分析,用不同方法解决,选择最优解题方法。这有利于开拓学生的思路,帮助学生掌握正确的思维方法,逐步提高思维的逻辑性、严密性和敏捷程度。本文拟举两例,分别用图示法和剖析法授以学生推理的方法,提高学生逻辑思维的能力。〔例一〕把一定量的Na_2CO_3、NaHCO_3和Na_2SO_4的混合物溶解在200毫升1.00M盐酸中,完全反应之后,生成2016毫升干燥的CO_2(在标准状况下)。然后加入400毫升0.100MBa(OH)_2溶液,使BaSO_4完全沉淀,再加40.0毫升1.00M盐酸恰好把溶液中过量的碱完全中和。最后把所得沉淀分离出来,测得干燥的BaSO_4的质量为1.48克。求这种混合物中三种化合物的质量百分组成。(84年高考化学试题) 分析:用图解法。
The key to learning to “dispel doubts” is to learn logical thinking. In the practice class, organize students to discuss some of the more complex issues, analyze them from different angles, use different methods to solve them, and choose the optimal problem-solving method. This is conducive to opening up students’ ideas, helping students master the correct way of thinking, and gradually improving the logic, rigor and agility of thinking. This article proposes two cases, using graphic and analytical methods to instruct student reasoning methods to improve students’ ability to think logically. [Example 1] A certain amount of a mixture of Na 2 CO 3 , NaHCO 3 and Na 2 SO 4 was dissolved in 200 ml of 1.00 M hydrochloric acid, and after complete reaction, 2016 ml of dry CO 2 was generated (under standard conditions). Then, 400 ml of a 0.100 M Ba(OH)2 solution was added to completely precipitate BaSO4, and 40.0 ml of 1.00 M hydrochloric acid was added to exactly neutralize the excess alkali in the solution. Finally, the resulting precipitate was separated and the mass of dried BaSO 4 was determined to be 1.48 g. The mass percent composition of the three compounds in this mixture is sought. (84 college entrance examination chemistry test) Analysis: Graphic method.