Learning chemistry includes learning the language of chemistry (names, formulae, symbols, and chemical equations) which has to be done in connection with the other areas of chemical knowledge. In this study we investigate how French students understand and use names (of chemical species and common mixtures) and chemical formulae. We set a paper and pencil test composed of open-ended and multiple choice questions (5 questions in total) to students (N= 603) who have been learning chemistry for 2 years (age 14) and others for up to 7 years (age 19, first year university). For all grade levels we found that the students have great difficulties understanding notions introduced right from the first two years of chemistry teaching. The scientific name opposed to a common name does not seem to be a relevant tool used by the students to classify chemical species and mixtures. They struggle to decode a chemical formula out of the context of a chemical equation and fail to decode them in that context. The students surveyed are not able to correctly associate with a name or a formula, both macroscopic (a pure substance or a mixture) and microscopic (an atom or a molecule) criteria. They seem to have mainly a microscopic reading of the names and the chemical formulae. Therefore we think that the language of chemistry could be a source of trouble for the learning of the notion of substance. These results confirm the need to offer teachers new didactical tools to develop the teaching of the language of chemistry.