A variation on the demonstration of the electrolysis of water at iron nails, using 1,10-phenanthroline and thymolphthalein, is described. The 1,10-phenanthroline is proposed as an alternative to the traditional potassium hexacyanoferrate(III) for detection of Fe2+ produced at the anode nail. Thymolphthalein, indicator for OH- generated at the cathode nail, provides a striking blue contrast to the orange tris(1,10-phenanthrolino)iron(II) complex cation. Three types of gelatin (Knox, agar, and Fisher G8) and aqueous 0.1 M sodium sulfate were used. The sharp contrast in the colors produced at the nails provides a highly effective demonstration of electrolysis and the diffusion of oxidized and reduced species from the electrodes. The effect of the electrolysis medium on the diffusion rates of the electrolyzed species is illustrated by comparison of the electrolysis in gelatinous and aqueous media.
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