The knowledge of historical facts can help teachers and students to correctly appreciate a variety of scientific theories. It is important to be aware of the evolution of the basic concepts, particularly the ones our students find very abstract and therefore difficult to understand. Historical knowledge of chemical concepts will allow us to understand their difficulties and make them easier to teach successfully. In this paper we answer the following research questions: what was the historic and sociologic context in which chemical equivalent, mole and its magnitude amount of substance were introduced to science? How the lack of historic knowledge in science teaching contributes to the presence of distorted views of science and hampers meaningful learning?