Colorful transitions of various acid−base indicators have been used to illustrate the concept of chemical equilibria, especially in spectrophotometric determination of the equilibrium constants or pK a values. To accommodate an online laboratory environment necessitated by the COVID-19 pandemic, this work employs color analyses from digital images to determine the pK a values of a double-range indicator thymol blue. The experiment has been developed into an online activity to teach chemical equilibria and dissociation of a diprotic acid. The pK a1 and pK a2 values determined by students are in good agreement with the literature values at 1.60 ± 0.05 and 8.70 ± 0.06, respectively. The results demonstrate a powerful application of RGB color analyses in determination of the pK a values of thymol blue without access to spectrophotometers.

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Eleven demonstration activities for an introductory undergraduate chemistry safety session are described. The first two activities are a safety video and a lab tour. All other activities are drawn from popular demonstrations and presented in the context of chemical safety. These include a balloon bursting via toluene, a dry ice fog created in a fume hood, a reaction forming a carbon snake, a glycerol and potassium permanganate reaction, creation of a fireproof banknote, a candle extinguished by a copper coil, a candle extinguished by a test tube, a demonstration of a can crushed by air pressure, and creation of a soda geyser. The pedagogical narratives of these demonstrations cover all four areas of chemistry safety learning outcomes using the RAMP approach (recognizing hazards, assessing risks, minimizing risks, and preparing for emergencies) recommended for undergraduate students by the American Chemical Society.

Homemade colorimeters using simple parts are excellent in undergraduate teaching labs as they allow students to learn instrument components and principles behind absorbance measurements. However, the absorbance values measured from such instruments often differ from those determined by commercial spectrophotometers. This work provides a step-by-step calculation of absorbance, taking into account of the properties of each component. Using a Si-photodiode detector (PD) and a light-dependent resistor (LDR), we show how the absorbance measurements depend on the spectral irradiance of the light source, the absorption spectrum of the sample, and the responsivity of the detectors. The provided calculation can help undergraduate students visualize how these factors contribute to optical measurements. It can serve as an experiment to introduce concepts of instrumentation and analysis of its performance.