Upgrading Smartphone RGB Colorimetry for Rapid Determination of Hydrogen Peroxide Decomposition Kinetics

Abstract The determination of the pseudo-first-order rate constant (k) for the catalytic decomposition of hydrogen peroxide is a fundamental experiment in general chemistry education. Traditional titration or gas-volumetric methods are laborious, require substantial reagents, and often yield inconsistent results. Inspired by the principles of intelligent chemistry (i.e., the integration of smart-device-based measurement and automated data analysis), we present an enhanced methodology that integrates the potassium titanyloxalate–H2O2 color-forming system with smartphone-based RGB blue-channel analysis. This experiment was implemented with 28 undergraduate students, who successfully determined activation energy using only a smartphone and a Python script. The color of this orange-yellow complex exhibits a broad absorption spectrum in the range of 430–470 nm (B channel). A linear calibration curve (R2 = 0.9902, 0.1–1.5 mM) was established by correlating the B value (i.e., this is the blue value in the RGB image) with the concentration of H2O2. Sequential images captured throughout the reaction process provided concentration–time profiles that were analyzed with first-order kinetics. Activation energy (Ea), calculated from the Arrhenius plot (ln k vs 1/T) at temperatures ranging from 5–45 °C, was 44.8 ± 2.4 kJ mol–1, showing excellent consistency with the value determined by UV–Vis spectrophotometry (44.8 ± 0.07 kJ mol–1). Compared to titration and gas-volumetric methods, our method eliminates specialized apparatus requirements, reduces the experimental duration to approximately 45 min, markedly decreases reagent consumption, and improves reproducibility (RSD < 5%). Translating to a sustainable and scalable learning experience, this cost-effective, digitalized procedure transforms the undergraduate kinetics laboratory into an active learning environment.