Students’ Identification and Application of Models to Rationalize Organic Acid-Base Trends
Acid - base chemistry is an essential component of the undergraduate chemistry curriculum. Acid - base concepts are introduced in general chemistry and expanded on in organic chemistry, b iochemistry, and other advanced chemistry courses. Through a mixed approach of surveys and think - aloud interviews, the proficiency of second - semester organic students in acid - base chemistry was measured. Students were given two questions, both requiring th em to rank the acidity of three compounds and justify the ranking. The first question focused on substituted carboxylic acids, and the second question focused on substituted aromatic structures. Although most students were able to correctly rank both sets of molecules, the correctness of their justifications was structure - dependent. Students did better at justifying the acidity of the aromatic structures, but while they were more successful at ranking the acidity of the substituted carboxylic acid structure s, students were largely unsuccessful at justifying the trend. Students often relied on memorization, attributing acidity to the presence of specific functional groups or substituents. Specific alternative conceptions observed in both surveys and interview s include the idea that resonance structures are always central in justifying properties for molecules that have π bonds, and that alkenes and alkynes have differing numbers of resonance structures given they have different bond orders. Finally, students h ad difficulty with identifying the most acidic proton and often selected sites based on content that could be memorized from lectures. Students were also asked to report their confidence in their answers on a 6 - point Likert scale from 0 – 5, and statisticall y significant differences were observed between students who ranked compounds correctly versus incorrectly for both questions in the study. However, when comparing the correctness of the justifications, a statistical difference between reported confidence was only observed with the aromatic structures question. The substituted carboxylic acids question required the application of models and ideas that extended beyond memorization.
