Inhibition of the corrosion of pure aluminium by nitrite and chromate anions in near neutral aqueous chloride solution has been studied by electrochemical impedance spectroscopy, keeping the ionic strength constant by addition of potassium sulphate electrolyte. Negative of the chloride pitting potential impedance spectra show that both anions are successful in reducing corrosion through adsorption, nitrite more than chromate. Positive of this value, nitrite becomes ineffective, whereas chromate remains adsorbed and continues to prevent pitting corrosion, probably through its ability to repair defects in the oxide film. Impedance techniques successfully show the qualitative and quantitative differences between the two inhibitors.