The basic concepts of optical absorbance and transmission are readily demonstrated by the student in a series of colorimetric titrations carried out in a titration cell installed in a rapid scanning spectrocolorimeter. The student observes color changes in the titration cell and relates them to the spectral transmission curve of the solution, which he sees simultaneously on an oscilloscope. The process of formation of new species at each stage of the titration can be followed. The student can also readily demonstrate isosbestic points. A further method is presented for determination of the endpoint of a titration by simultaneously comparing the absorbance of the liquid at any two wavelengths in the visible region.

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