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

This study aims to develop an alternative method for the determination of the chemical equilibrium constant (Kc) 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 Kc 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 Kc 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 Kc 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.