Olfactory titration

A very different source, vanillin, has also given accurate results. A saturated solution of vanillin is prepared by dissolving vanillin in ethanol and by adding a small portion of this solution to the basic analyte solution, NaOH. This type of olfactory titration is more appealing to students due to the pleasant aroma of the vanillin. Instructors might find this titration more attractive as well since the concentration of the NaOH is only 1M versus the 2 M required to quench the aromas of onions and garlic. A detailed account of the chemistry involved, procedures, and student handouts is available (Neppel et al. 2005). 

Neppel, K., M. T. Oliver-Hoyo, C. Queen, and N. Reed (2005) A closer look at olfactory titrations. Journal of Chemical Education 82(4), 607-610. 

Wood, J. T. and R. Eddy (1996) Olfactory titration. Journal of Chemical Education 73(3), 257-258. 

The titrimetric modifications described above exemplify either an instrumental adaptation (as in the case of the potentiometric and conductometric titrations) or a chemical manipulation (olfactory indicators). The first uses the sense of hearing, while the latter type appeals to the sense of smell. Unfortunately, instrumental adaptations that utilize one-of-a-kind homemade instruments are not readily available to the typical educator or may even be out of circulation. Also considered is the fact that at institutions where the enrollment of handicapped people is low, the justification of specialized equipment can be very difficult to obtain. On the other hand, the chemical manipulations discussed rely on readily available chemicals (onions and cloves) and represent comparable costs and laboratory preparation times as traditional titrimetric experiments. Since all students may perform these... 

Flair, M. and W. N. Setzer (1990) An olfactory indicator for acid-base titrations. Journal of Chemical Education 67(9), 795-796. 

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