A version of the visible spectrophotometry method is applied
to quantitate salicylate in a commercial product and also
in an instructor-prepared unknown solution. The Beer–Lambert
law is followed over the concentration range of interest (10–100
mM), and a linear calibration curve is prepared. For the analysis
of the commercial face wash, we collected and posted all trials
for the entire class and asked students to conduct a t test comparing
their data to that of the class. In addition, students compared
their results with the salicylic acid value provided by the
manufacturer. This requires students to practice unit conversions
from amount concentration to mass concentration expressed as
a percentage. Typical student results for this analysis compare
favorably to the salicylic acid level that the manufacturer claims.
A recent class at Emporia State University (8 students, 24 analyses)
determined an average salicylic acid concentration of (1.01
± 0.09)% compared to 1% listed by the manufacturer (only one
significant figure provided). While these results generally confirm
the accuracy of the analysis, synthetic unknown solutions