Know Your Unknowns

The third laboratory of the semester in introduction to organic chemistry lab, we did a simple liquid-liquid extraction that was basically a scaled down version of the lab that I have been doing in majors organic chemistry. The procedure separated a nonpolar compound (biphenyl or camphor) from an organic acid (benzoic or cinnamic acid). I create a little intrigue by focusing the lab on the identification of the unknowns that were separated by liquid-liquid separation (four possible combinations of biphenyl, camphor, benzoic acid, and cinnamic acid). In the majors lab we identify the unknowns by melting point, but I used TLC to identify them for this experiment. TLC can be done with solutions and wet compounds without waiting for the compounds to dry out. We could even spot the organic phase of the liquid-liquid extraction without evaporating the solvent (methyl t-butylether). The use of unknowns is a traditional way to add an element of discovery to experiments that I think is very effective. Unknowns also function as a means to reward good/careful technique.

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