乙醇-水介质中氟-铝沉淀电位滴定体系研究

Studies on Potentiometric Titration System of Precipitation of Aluminium-Fluoride in Ethanol-Water Midium

由于氟-铝的多级络合反应,在水溶液中用氟化物直接滴定铝没有明显的电位突跃,若用乙醇-水介质,则电位突跃明显.本文对乙醇-水介质中氟-铝沉淀电位滴定体系的化学平衡进行了研究.测定了在不同浓度的乙醇介质中氟-铝的络合比及各级络合物的稳定常数等参数.实验表明用F^-电位滴定测定铝可取得较好结果.

The present paper covers the chemical equilibriums of precipitation of aluminium with fluoride in ethanol-water midium. The successive stability constants for aluminium-fluoride were determined in the complexation domain of the titration curve. The solubility product of the precipitation of Na3AlF6 was calculated in precipitation domain of the titration curve. The effect of pH on the equilibrium was theoretically investigated. The additional proton constants of fluoride ion were determined in water and ethanol midium with different concentrations. The values are found to be in fair agreement with literature data.The titration system was tested by standard recovery and standard sample analysis. Recovery ratio is 100±0. 6%. The relative errors for standard sample analysis are less than 1%. It is shown that the system for aluminium-fluoride potentiometric titration is valid.