Silica gel was chemically modified with Congo red and characterized by Fourier transform infrared spectroscopy, elemental and thermogravimetric analysis. The pH-sensitive immobilized Congo red retains the same properties as its solution counterpart and could be applied as solid indicator. The functionalized silica gel was also employed to extract different cations from water solutions. The concentration of cations extracted was determined by inductively coupled plasma optical emission spectrometry. The solid support is able to selectively extract silver and copper from water solutions and retains its properties after treatment with different organic and inorganic solvents.