pK of An Indicator

Not carried out.

Students determine the pK using the spectrometer. Each student pair first uses the Measurenet station as a pH meter to prepare a series of buffer solutions covering the pH range in which a chosen indicator changes from one of its forms to another. Students then use each buffer solution to prepare a final solution containing a fixed total concentration of the indicator and measure its absorption spectrum. Analysis of the resulting set of spectra readily yields the pK value.

Having the entire spectrum of each sample is very helpful to aid in identifying any suspect measurements that might need repeating.