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A Simple Experiment for Ion Migration

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Karl E. Bessler and Daniel de Oliveira Campos

Universidade de Brasília, Departamento de Química, C.P. 04478, 70919-970 Brasília, DF, Brazil

J. Chem. Educ., 1999, 76 (11), p 1516

DOI: 10.1021/ed076p1516

Publication Date (Web): November 1, 1999

Abstract

A simple, versatile, and low-cost version of a qualitative ion migration experiment is presented, which needs a minimum amount of chemicals and can be performed by inexperienced students. In the experiment cations and anions (preferably colorless or faintly colored) migrate toward one another and on combination produce insoluble and strongly colored compounds. A strip of filter paper supported on a glass plate and soaked with an electrolyte solution (NH₄NO₃) is used as migration medium. The paper is spotted with a suitable pair of solutions containing the reactive ions using a capillary pipet. A tension of 30-V dc is applied using graphite electrodes. The result is observed within 10 minutes: at the meeting point of the two ions the reaction product precipitates, forming a sharp colored spot on the filter paper. The following ion combinations have been used successfully: Pb²⁺/I^-, Hg²⁺/I^-, Ag⁺/I^-, Pb²⁺/CrO₄^2-, Cu²⁺/[Fe(CN)₆]^4-, Fe³⁺/[Fe(CN)₆]^4-, Fe²⁺/[Fe(CN)₆]^3-, and Zn²⁺/[Fe(CN)₆]^3-.