This study presents a transformative approach to electrochemical impedance spectroscopy (EIS), advancing it from a traditionally empirical technique to a robust, predictive tool for real-time ion sensing. By developing a first-principles model that links electrode/electrolyte interfacial processes to impedance responses, we have provided a deeper understanding of the physico-chemical dynamics governing EIS behavior. Our model not only accurately predicts differential capacitance and explains non-ideal impedance behaviors such as the constant phase element (CPE) but also reveals fundamental correlations between ion properties and impedance spectra.