This article proposes an indirect method to evaluate the corrosion rate of iron nail in simulated seawater. The official procedure is based on the direct measurement of the specimen's weight loss over time; however, a highly precise scale is required and such equipment may not be easily available. On the other hand, mobile phones equipped with good built-in cameras have become an essential part of everyday lives of students and educators. With the built-in cameras, students followed the formation of the colored complex from the reaction between released iron ions and 1,10-phenanthroline. The images were then decomposed into the RGB channels that were converted into absorbance. Another point worth mentioning is that rather than providing students with a step-by-step procedure, the instructor used a problem-based approach that enabled students to develop the experimental procedure themselves. This project-driven interdisciplinary experiment engaged students into thinking and producing the experiment. Finally, bringing cell phones into science teaching was very helpful as it made learning more inviting and meaningful.