The present paper deals with some questions that can cause difficulties for the understanding of the concepts of amount of substance and the mol by Chemistry students. The paper also seeks to investigate, historically, the origin of the concept of amount of substance, presenting the context in which this concept occurs in interaction with other concepts, stressing the need for teachers and pupils to understand the scientific concepts thoroughly, not being limited only to definitions.
amount of substance and mol; teach-learning of scientific concepts; epistemological difficulties; history of Science