The notion that acid salts exist only for diprotic and polyprotic acids is found in many high school and university textbooks, although the "only" condition is not always stated explicitly. A fairly simple experiment shows that there is a pronounced exothermic effect when pure acetic acid is added to potassium acetate. Experiments with similar reactions between other pure monoprotic acids and their corresponding salts were also carried out. In all cases, a pronounced exothermic effect could be detected and an explanation is offered in terms of formation of acid salts. All of the above salts contain strong hydrogen bonds in their structure (as may be unequivocally demonstrated by means of IR spectroscopy) and the existence of such intermolecular attractions is one of the factors leading to the exothermic effect. (Contains 2 tables and 4 figures.)