Relation Between Electromotive Force and Ion Concentration in Direct Potentiometric Method
ZHOU Yan-Feng1, XIE Qing-Ji2, CHEN Zhi-Xun1
1. Hunan Nonferrous Metals Vocational and Technical College, Zhuzhou 412006, China;
2. College of Chemistry, Hunan Normal University, Changsha 410081, China
Abstract This paper discovered the reason of the inconsistence of the theoretical formula and the measured data was that the theoretical formula was deduced according to the condition that reference electrode was connected to the positive electrode in composite electrode, however, in the test, it is not the reference electrode that connects with the positive electrode in composite electrode, but the indicating electrode. Based on this, we further explored the equation of EMF and ion concentration in the case of substance to be determined being the anion or cation:Ecell=K±0.059 2/nlgci. The conclusions are as follows:(1) In the equation,+ or-of the sign behind K, in other words, with the increasing of measured ion concentrations, whether electromotive force will be rising or not depends on the charge of the ion itself and the connection between the indicator electrode and the reference electrode with positive negative pole of apparatus;(2) Quantitative calculation in standard comparison method and standard addition method also needs to consider the positive or negative sign behind the K. The quantitative formula is not the same under different conditions. It is suggested to calculate the sample content by combining the Nernst equation.
ZHOU Yan-Feng, XIE Qing-Ji, CHEN Zhi-Xun. Relation Between Electromotive Force and Ion Concentration in Direct Potentiometric Method[J]. Chinese Journal of Chemical Education, 2017, 38(18): 78-81.
