Eugenol:An Olfactory Acid/Base Titrative Indicator

[methyl_ethyl]

I hated to start a new thread just for this topic however I thought it would be off topic in any of the other threads that are currently being discussed.  I guess this could be the thread that discusses how to integrate visually handicapped students into the chemistry lab.  Although the visually impaired may not be able to read the burette, I guess just being able to determine the end point is a step in the right direction.  Then again I am not sure how good I feel about visually impaired students in the chemistry lab at all.  Well at least someone is trying to find ways to integrate them in the classroom laboratory.
I wonder if there are many visually impaired chemists in the industry?  This is not a topic that I am passionate about, just something I found whilst scouring the web, thought it was noteworthy and interesting....     


An Olfactory Indicator for Acid Base Titrations
A Laboratory Technique for the Visually Impaired
Mark N. Flair' and William N. Setzer
Journal of Chemical Education Volume 67 Number 9 September 1990

Eugenol proved to be completely successful as an olfactory indicator for acid-base titrations both in terms of the obvious endpoint of the titration (the pungent fragrance of cloves bursts out of the titration mixture at the equivalence point) and the consistency of the results. The results of our titrations using both eugenol and phenolphthalein are summarized in Tables 1 and 2. The data in Table 1 show that titrations using a eugenol indicator are as reproducible as those using phenolphthalein. Note, however, that the eugenol endpoints require about two drops less acid than the phenolphthalein endpoints. That is, after the endpoint of the titration was determined by the strong smell of cloves, phenolphthalein indicator was added giving a pink solution and titration continued until the visual endpoint (colorless) was obtained. The difference in endpoints is perhaps due to the difference in pKa values for the indicators (pKa of eugenol = 10.0, pKa of phenolphthalein = 9.7, and pKa of thio- phenol = 6.513 ).

regards,

methyl_ethyl

[Rhodium]

Although the visually impaired may not be able to read the burette, I guess just being able to determine the end point is a step in the right direction.

It is probably useful to colorblind people, rather than the severely myopic.