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统编初中化学,关于“物质结晶”的“升温、增剂、加质”中,涉及到的计算问题,对刚学化学的初中学生来说,的确是一个难点,教者也感到很棘手。过去习惯上采用列比例分步解题法,如溶液法,溶剂法等,这些计算步骤烦琐,多数要计算几步才能得到结果,初中学生难以掌握。在近几年的教学实践中,我们对这类计算方法经反复研究,归纳出用“终止温度法”一步列式计算的方法,不但把复杂的计算步骤简化了,也取得了较好的教学效果。“终止温度法”是根据溶解度概念,同温下饱和溶液的质量百分比浓度相等的原理得出的。可用下列一般通式表示:
In junior high school chemistry, the calculations involved in “material crystallization” in “heating up, adding agents, and accelerating ” are really difficult for junior high school students who just studied chemistry. Feeling very tricky. In the past, it was customary to use the column-by-column step-by-step solution method, such as the solution method and the solvent method. These calculation steps are cumbersome, and most of them require a few steps to get the results. It is difficult for junior high school students to grasp. In the teaching practice in recent years, we have repeatedly studied this type of calculation method and summed up the method of using the “stop temperature method” and the “step-by-step calculation method”. This not only simplifies the complicated calculation steps, but also achieves better results. Teaching effect. “The termination temperature method” is based on the concept of solubility, and the principle of equal mass concentration of saturated solution at the same temperature. The following general formula can be used: