Compounds in this group are generally nonflammable.

Weak acids are generally soluble in water with the release of hydrogen ions. The resulting solutions have pHs of less than 7. Acids neutralize chemical bases (for example: amines and inorganic hydroxides) to form salts, liberating heat. Neutralization occurs as the base accepts hydrogen ions that the acid donates. These materials react with active metals, including such structural metals as aluminum and iron, to release hydrogen, a flammable gas. They can initiate the polymerization of certain classes of organic compounds. They react with cyanide compounds to release gaseous hydrogen cyanide. They often generate flammable and/or toxic gases in contact with dithiocarbamates, isocyanates, mercaptans, nitrides, nitriles, sulfides, and 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 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. Weak acids dissociate in water to H+ ions and weak conjugate base anions although they do not fully dissociate like strong acids. Acids are considered weak if they have a pKa value greater than -2, or pH greater than 2 but less than 7.

Arsenic acid, boric acid, linolenic acid, phosphoric acid, selenious acid, hydrofluoric acid.