The pH scale has a range of 0 to 14, with water having a pH=7, or neutral. A pH of 1 indicates an acid (i.e. hydrochloric acid), whereas a pH of 14 (i.e. drain cleaner, lye) indicates an alkaline (base). Since it is a logarithmic scale measuring the level of Hydrogen ions, a change of one pH unit is a change in H- ions by a level of 10.
Pour water into water, and there is no reaction. However, pour one part acid (pH2) into one part of water (pH7) and you will see a reaction, resulting in ~pH3. A reaction can be as simple as slight fuming, or as violent as an explosion. The reaction occurs due to oxygen and hydrogen molecules rearranging themselves.
EPA defines a liquid being a corrosive acid as having a pH=2 or lower. EPA requires such waste to be accounted for on a hazardous waste manifest with a RCRA assigned characteristic code of “D002”. An acid with a pH=2 is quantum leaps more reactive than that of pH=5. Thus, it’s hazard level is much more severe.
For example, a lemon contains citric acid. The acid is around pH=2.2, but it does not severely burn your tongue because the concentration of the acid is only around 6%. The same concept of reactivity occurs for alkaline liquids with pH=8 through 14. There are many chemicals that can hurt both your environment and health. Contact MLi Environmental for more info, and quotes for chemicals disposal.