limiting molar conductivity of a strong electrolyte can be determined by graphical extrapolation methode for suggest a methode for the determination of limiting molar conductivity of a weak electroliyte taking acetic acid ( CH3COOH ) as example
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ABSTRACT
Undergraduate experiments on ionic conductivity are common practice in general chemistry and advanced physical chemistry laboratories. Often, the conductivities are measured for solutions prepared for various salts, in a range of concentrations, and the relationship between solution conductivity and concentration is interpreted in terms of the Kohlrausch law. Contaminations can dominate the conductivity of the solutions such that students might obtain unsatisfactory results for analysis. Here, the experience of using a simple experimental procedure to obtain the concentration dependence of ionic conductivities for very dilute (sub-millimolar) electrolyte solutions in undergraduate laboratories is described. The experiment consists of measuring the conductivity of solutions of increasing concentration prepared by dropping the electrolyte solution into an initial vessel of deionized water. The range of concentrations achieved is one in which the conductivities vary linearly with the concentrations, such that the molar conductivities can be obtained directly without the use of the Kohlrausch equation. The simplicity of the experimental procedure leads the students to obtain good quality results using minimal amounts of materials. Examples are presented for the conductivities of strong electrolytes, and for the weak acetic acid electrolyte, for which the conductivity is dependent on the degree of dissociation also for dilute solutions.
Keywords: conductivity; Kohlrausch law; undergraduate laboratory; physical chemistry; electrolytes
SUMMARY
In this article, we describe the implementation a simple method to prepare solutions of very low (sub-millimolar) concentration, to be used in the study of the conductivity of electrolyte solutions in general chemistry or physical chemistry undergraduate laboratories. The method consists in preparing solutions with increasing concentration by dropping the electrolyte solution into an initial sample of deionized water. The procedure saves material and is robust in the sense that the manipulation of the solutions is minimal, such that the students frequently obtain satisfactory results. The range of concentrations obtained is such that the limiting molar conductivities of strong electrolytes can be obtained with good accuracy without the use of Kohlrausch law, directly from the molar conductivity of the solutions, which is essentially constant at the concentration ranges sampled. The method can be used also to study the dissociation equilibrium of weak electrolytes by means of the Ostwald dilution law. The method was satisfactorily applied in first-year General Chemistry and second-year Physical Chemistry laboratories.
Answer:
The limiting molar conductivity of weak electrolytes can be determined by using Kohlrausch law.