Smartphone-assisted colorimetric determination of chemical equilibrium constant (K _c ) as an alternative method in high school chemistry

Abstract This study aims to develop an alternative method for the determination of the chemical equilibrium constant (K c ) of thiocyanatoiron(III) complex ion, based on colorimetric analysis of smartphone-captured images. The various pictures of the complex ion captured by smartphones were processed using ImageJ software to determine the K c using a standard plot between blue color intensity and −log[[Fe(SCN)] 2+ ]. The dependent samples t -test analysis at the 95 % confidence level ( p < 0.05) indicated that the K c obtained from colorimetric methods from smartphones and the standard UV–Vis spectroscopic method were not statistically different. This experiment was implemented as three 2-h inquiry learning activities on the chemical equilibrium topic for one classroom of 40 grade-11 students in Thailand. Their K c values were in the range of 200–250, which is consistent with our preparation result. It was found that the students obtained post-conceptual test scores (mean 8.75, S.D. 0.90) statistically higher than pre-conceptual test scores (mean 3.50, S.D. 0.78) at the 95 % significance level. These students commented that this experiment was easy to perform, and they enjoyed using their smartphones in studying chemistry.