化学里,有一些对“反应过程中某种量的变化”进行分析的问题。这些问题难度大,往往使学生盲目乱猜。在教学中,笔者从“极限”的角度给予解答,收到了良好的教学效果,现举两例,加以说明。 [例一]电解氯化铜溶液时,溶液的pH值怎样变化? 一般认为:氯化铜属强酸弱碱盐,溶液显酸性。随着不断电解,氯化铜浓度减小,溶液的酸度减小,pH值增大。但也有人认为:随着氯化铜浓度减小,水解程度增大, In chemistry, there are problems with analyzing “a certain amount of change in the reaction process.” These problems are difficult and often lead students to blindly guess. In the teaching, the author answered the question from the perspective of “limit” and received good teaching results. Now, two examples are given to illustrate. [Example 1] When electrolytic copper chloride solution is used, how does the pH value of the solution change? It is generally believed that copper chloride is a strong acid and weak base salt and the solution is acidic. With continuous electrolysis, the concentration of cupric chloride decreases, the acidity of the solution decreases, and the pH increases. However, some people believe that as the concentration of copper chloride decreases, the degree of hydrolysis increases.