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学生在学习《酸碱中和滴定》一节时,常提出以下几个问题: 1.强酸强碱完全中和时,溶液的pH值=7,甲基橙,酚酞的变色范围均不在pH=7时,为何能用来判断滴定终点? 2.甲基橙、酚酞是否适用在任何浓度的强酸强碱的中和滴定中作指示剂? 3.石蕊的变色范围pH值是5.0—8.0,为什么在进行中和滴定时,一般不选它作指示剂?这些问题,我是采用如下办法解决的。
Students study the “acid-base neutralization titration” section, often ask the following questions: 1. Strong acid and alkali completely neutralized, the pH of the solution = 7, methyl orange, phenolphthalein discoloration range are not in the pH = At 7 o’clock, why can I use to judge the titration end point? 2. Is methyl orange and phenolphthalein used as indicators in the neutralization titration of strong acid and alkali at any concentration? 3. The discoloration range of litmus is 5.0-8.0, Why is it generally not selected as an indicator when conducting a neutralization titration? These problems are solved by the following methods.