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一、前言由于Al~(3+)易水解,在低酸度时与EDTA生成羟基络合物,同时Al~(3+)和EDTA的络合反应速度较慢,而且稳定常数(logK_(AIY)=16.1)又不太大,直接滴定容易发生误差,所以目前使用最多的是返滴定法和氟化物置换滴定法。此两法为了增加反应速度均需加热至沸,而且氟化物有污染问题。为此,P＇_((?)b1)提出CyDTA(环已烷二氨四乙酸)来代替EDTA,可在室温下和大量的中性盐(Na、K盐)存在下,以XO(二甲酚橙)为指示剂,用六次甲基四胺调节pH5.5～6,用Pb(NO_3)返滴定过量的CyDTA
I. INTRODUCTION Due to the hydrolysis of Al ~ (3 +), the formation of hydroxy complexes with EDTA at low acidity is slow, and the complexation reaction between Al ~ (3+) and EDTA is slow. The stability constant (logK_ (AIY) = 16.1) is not too large, direct titration prone to error, so the most commonly used is the back titration and fluoride replacement titration. The two methods in order to increase the reaction rate are heated to boiling, and fluoride pollution problems. For this purpose, P’_ ((?) B1) proposes that CyDTA (cyclohexanediaminetetraacetic acid) instead of EDTA can be used at room temperature in the presence of a large amount of neutral salts (Na, K salts) Cresol orange) as an indicator, with hexamethylenetetramine pH5.5 ~ 6, with Pb (NO_3) back titration of excess CyDTA