Abstract It is mentioned in the electromotive force experiment of the physical chemistry that the anion and cation transference number values of KCl aqueous solution are close to each other,but the method of determination is unknown.This experiment is designed to use the Hittorf’s method experimental setup,which is available in most physical chemistry laboratories in China,and is simple and easy to perform without environmental pollution.However,if only KCl solution were used,there would be an environmental and safety problem that Cl- would be oxidized in the anode area and toxic Cl2 would give off.This innovative experiment addresses on the above issues and proposes an upgraded two-compartment Hittorf apparatus,which is based on the essential characteristic of electron loss at the electrolyte/electrode interface during electrochemical oxidation.Besides the KCl solution,the KOH solution is connected in series via a salt bridge in the anodic region,where KOH contacts the power supply’s positive electrode.Thereby the anodic reaction is transformed into that the OH- anions lose electron at the electrolyte/electrode interface to give off O2.Moreover,the concentration change of the Cl- in the cathodic region is obtained by precipitation titration(the Mohr’s method),which is related to the basic knowledge of solubility product of insoluble salts in physical chemistry.Then the transference number values of the Cl-,K+ are calculated to be 0.500 and 0.500,respectively,and verified to be close to each other.This experiment not only upgrades the experiment of Hittorf’s method for determining transference number,but also provides an in-depth understanding of the principle of saturated KCl solution as a working solution for both salt bridge and saturated calomel reference electrodes,together with broadening the application scenario of salt bridge.It also triggers students’ interest in designing experiments by applying the knowledge points of standard electrode potential,solubility product,and precipitation titration.Thus,it helps to improve the experimental teaching level of physical chemistry in terms of both breadth and depth.
JIANG Shu-Han, ZHANG Xin-Tong, LIU Xin, CHEN Ya-Xuan, ZHANG Ren-Jie. Determination of Ion Transference Number of KCl Aqueous Solution by Improved Hittorf’s Method[J]. Chinese Journal of Chemical Education, 2026, 47(4): 62-68.
