A Modest Change to a Freshman Kinetics Experiment that Reduces Lab Time without Compromising Student Results

Russell, Arlene A.; Casey, Jennifer R.; Barr, Kristopher K.

doi:10.1021/acs.jchemed.2c00744

Cited by 1 publication

(1 citation statement)

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“…In university experiments of reaction , usually a UV–visible spectrometer is used to monitor the change of the concentration of In 2– , [In 2– ]( t ). However, the spectrometer setup is costly, limiting its popularity. In addition, most of the laboratory classes mainly emphasize the kinetics of the forward reaction .…”

Section: Introductionmentioning

confidence: 99%

Kinetics of the Color-Fading Reaction of Phenolphthalein in Alkaline Solution Studied with a Simple and Economical Device

Luo,

Wu,

Lin

et al. 2023

J. Chem. Educ.

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A simple photometric device was built to measure the kinetics of the title reaction. The device consisted of a green light-emitting diode (centered at 520 nm), a sample vial, a photodiode, and an Arduino microcontroller board. These parts were mounted on a black poly(lactic acid) holder which was manufactured by utilizing three-dimensional printing. Adequate sensitivity and dynamic range (linear detection range from 2 × 10–3 to 0.9 in absorbance, base 10) and time resolution (ca. 6 × 10–3 s) have been achieved. The time-resolved absorbance of the pink form of phenolphthalein was recorded automatically. The time scale of the forward reaction can be controlled by [OH–]. Evidence of reaching a chemical equilibrium was observed at conditions of higher concentration of phenolphthalein and lower [OH–]. We also demonstrated direct observation of the slow reversed reaction (taking ca. hours). Factors affecting the reaction kinetics like the ionic strength and organic solvents have also been tested. For a laboratory class, the basic goal may include the kinetics of the forward reaction and a simple description of the chemical equilibrium. If time allows, the reversed reaction (color reappearing) may be demonstrated. In a test run, the participating high school students positively agreed that this activity had increased their related ability, while a minor portion of them were less confident on more complicated knowledge items like using the Beer–Lambert law, measuring the lifetime, and knowing the evidence of the reverse reaction.

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Section: Introductionmentioning

confidence: 99%