Aluminium oxide as an amphoteric base. Footage of aluminium (III) oxide (Al2O3) being added to an acid, with the results monitored using a pH probe. The probe is in the beaker, with the pH reading displayed at right. An amphoteric chemical is one that can react with and neutralise both acids and bases. Here, the aluminium oxide is reacting with an acid, acting as a base to neutralise it. As the reaction progresses, the pH has changed from acidic (below 7) to neutral (7) by the end of the clip.