Here, students determine the total phenolic content in beers using the Folin–Ciocalteu assay. The Folin–Ciocalteu reagent is a yellow complex, in an alkaline medium; it reacts with phenols and non-phenolic reducing substances to form a blue complex. Quantitative analysis was carried out using absorbance measured at 765 nm (standard method) and digital images (proposed method). In the proposed method, samples were placed in a 96 microwell plate; then, a plate image was obtained with a flatbed scanner. The ImageJ plugin ReadPlate extracts red (R)-values from all wells of the scanned image at the same time; then, R-values were exported to a spreadsheet that converted these values to absorbances. Using absorbances obtained with R-values, the spreadsheet also provides standard calibration plots, limits of detection (LODs), limits of quantification (LOQs), and beer sample total phenolic contents. The proposed method and the standard method were compared using two-tailed significance tests; students observed that both methods provide equivalent results, that both methods were linear in a 2–10 mg L–1 gallic acid concentration range, and that both methods had close LODs and LOQs, 0.55 and 1.70 gallic acid mg L–1, respectively. Beer sample total phenolic contents were compared using one-tailed significance tests. This laboratory experiment provides an effective instrumental alternative to spectrophotometric methods, which can be especially beneficial, where purchasing and maintaining a spectrophotometer is a challenge, and it also presents to the students one-tailed and two-tailed significant tests.

Herein, analytical chemistry students determine the [Fe(H2O)6] 3+ + CSN- [Fe(H2O)5(SCN)] 2+ + H2O reaction equilibrium constants. [Fe(H2O)6] 3+ has a slight yellow color, CSNis colorless and [Fe(H2O)5(SCN)] 2+ are deep blood-red (λmax = 447 nm). Thus, the reaction is easily observed. Equilibrium constants were calculated using eight [Fe(H2O)6] 3+ (0.002 mol L-1) and SCN-(0.002 mol L-1) mixtures, [Fe(H2O)5(SCN)] 2+ concentrations were determinate using absorbance measured at 447 nm and RGB values extracted from digital images, which were obtained with a flatbed scanner. The paired t test showed that equilibrium constants determine using absorbance and digital images were statistically equivalent, at 95 % confidence interval. Additionally, students evaluated how well a calibration curve follows a straight-line using correlation coefficient, analysis of variance (ANOVA) and residual plots. A Microsoft Excel spreadsheet was provided in Google Drive, this Table organize data, provides calibration plots and determine equilibrium constants in the eight Fe 3+ and SCNmixtures. This laboratory practice was carried out with 14 chemical engineering students working in pairs in Universidade Regional de Blumenau, it takes over 120-150 minutes. Extraction of RGB values from digital images and data analysis was carried out in a separate 50 minutes class.