High Quality Content by WIKIPEDIA articles! Perchloric acid is the inorganic compound with the formula HClO4. Usually encountered as an aqueous solution, this colourless compound is a strong acid comparable in strength to sulfuric and nitric acids. It is a powerful oxidizer, but its aqueous solutions up to appr. 70% are remarkably inert, only showing strong acid properties and no other oxidizing properties. Above concentrations of appr. 70% the speed of oxidizing reactions rapidly increases with increasing acid concentration. It is useful for preparing perchlorate salts, especially ammonium perchlorate, an important rocket oxidizer. Perchloric acid is also dangerously corrosive and readily forms explosive mixtures.