Materials in this group are generally nonflammable. They may accelerate the combustion of other materials by providing oxygen to the combustion site, that is, by serving as oxidizing agents.

Materials in this group are generally soluble in water with the release of hydrogen ions. The resulting solutions have pHs of 1 or near 1. Materials in this group react with chemical bases (for example: amines and inorganic hydroxides) to form salts. These neutralization reactions occur as the base accepts hydrogen ions that the acid donates. Neutralizations can generate dangerously large amounts of heat in small spaces. The dissolution of acids in water or the dilution of their concentrated solutions with water may generate significant heat. The addition of water to acids often generates sufficient heat in the small region of mixing to boil some of the water explosively. The resulting "bumping" spatters acid widely. These materials have significant ability as oxidizing agents, but that ability varies (for example, nitric acid is a stronger oxidizing agent than sulfuric acid and most sulfonic acids). They can react with active metals, including iron and aluminum, and also many less active metals, to dissolve the metal and liberate hydrogen and/or toxic gases. The subsequent stability of the corrosion products (possibly nitrates) should be considered. Like other acids, materials in this group can initiate polymerization in certain classes of organic compounds. Their reactions with cyanide salts and compounds release gaseous hydrogen cyanide. Flammable and/or toxic gases are also often generated by their reactions with dithiocarbamates, isocyanates, mercaptans, nitrides, nitriles, sulfides, and weak or strong reducing agents. Additional gas-generating reactions occur with sulfites, nitrites, thiosulfates (to give H2S and SO3), dithionites (SO2), and even carbonates: the carbon dioxide gas from the last is non-toxic but the heat and spattering from the reaction can be troublesome. Acids often catalyze (increase the rate of) chemical reactions.

Corrosive to tissue. Acid fumes irritate sensitive tissues (such as the eyes and respiratory system) especially severely.

Acids have a sour taste; they turn blue litmus red. Strong acids completely dissociate in water to H+ ions and extremely weak conjugate base anions. Oxidizing acids dissociate to give anions that do act as oxidants. They possess a pKa value below -2, or a pH value less than 2.

Sulfuric acid, nitric acid, perchloric acid, chlorosulfonic acid, chloric acid, nitrosulfuric acid, selenic acid.