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新出版的高等师范院校“分析化学”试用教材对多元酸分步滴定条件提出:“如果二元酸的CKa_1>10~(-8),CKa_2>10~(-8),……;且当Ka_(1)/Ka_(2)>10~5时,两个H~+可分步滴定,形成两个突跃。”又提出:“如果二元酸的CKa_1>10~(-8),而CKa_2>10~(-8),且Ka_1>100Ka_2时,只有第一级离解的H~(+)被滴定,即在第一等当点形成突跃。”对于前一个条件,我们认为是无可非议的。至于第二个条件,是值得商榷的。本文拟从滴定反应的完全程度和终点误差两方面来论证多无酸碱分步滴定的条件。
Newly-published teaching materials for Analytical Chemistry at higher normal colleges and universities put forward the following conditions for step titration of polybasic acid: “if CKa_1> 10 ~ (-8), CKa_2> 10 ~ (-8) When Ka_1 / Ka_2> 10 ~ 5, two H + can be titrated step by step, forming two jumps. ”It is also proposed that“ if the diacid CKa_1> 10 ~ (-8) , Whereas for CKa_2> 10 ~ (-8) and for Ka_1> 100Ka_2, only the H ~ (+) dissociation of the first order is titrated, ie a jump is formed at the first equivalence point. ”For the previous condition, It is beyond reproach As for the second condition, it is debatable. In this paper, the titration reaction from the complete degree and the end point of error to demonstrate multi-acid-base step titration conditions.