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强碱滴定弱酸时,突跃范围正比于弱酸的浓度与电离平衡常数之乘积CKa.因此,如果弱酸的离解常数很小,或酸的浓度很低,达到一定限度时,就会使突跃范围大小,致使弱酸不能准确进行滴定.那么,这个限度是多少呢?这与所要求的准确度及检测终点的方法有关.如用指示剂来检测终点,要求滴定的误差≤0.1%,就是说:测定到等当点前后0.1%时,人眼借助指示剂的变色才能准确判断出来.但是要使人眼判断准确,滴定到等当点前后0.1%时,溶液的PH变化一般要在0.2单位
Strong alkali titration weak acid, the range of the sudden jump is proportional to the weak acid concentration and ionization equilibrium constant product of CKa. Therefore, if the weak acid dissociation constant is very small, or acid concentration is low, to a certain extent, it will make the sudden range Size, resulting in weak acid can not be accurate titration.Then, what is the limit? This is related to the required accuracy and method of detecting the endpoint.If the indicator is used to detect the endpoint, the titration error≤0.1% is required: Determination of equivalence point before and after 0.1%, the human eye by means of the indicator of the color change can be accurately judged.But to make the human eye to determine accurately, titration to the equivalence point before and after 0.1%, the PH changes in the solution generally 0.2 units