Studying chemistry includes learning the language of chemistry (names, formulas, symbols, chemical equations) (Laszlo, 2011; Taber, 2009). Learning this language should be done by understanding the concepts used by the chemist (Talanquer, 2011). As in mathematics education (Duval, 2006), using several semiotic systems poses numerous difficulties to students (Taskin & Bernholt, 2014). This difficulty is not always taken into account in chemistry teaching (Kaya & Erduran, 2013) and the teachers may not be aware of it (Mzoughi-Khadhraoui & Dumon, 2012). Thus, we conducted an investigation to find out how French students understand and use names (of chemical species and of common mixtures) and chemical formulas: do they make a distinction between scientific names and usual names in order to differentiate between chemical species and mixtures? To what extent do they master chemical formulas? We administered a paper and pencil test composed of an open-ended question and two multiple choice questions 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). In the first question the students are asked to classify names from a list including usual names and scientific names. In question 2, three pairs of chemical formulas (H2O and H2O2; O and O2; CH4 and C2H8) are given; for each pair the students have to say whether the formulas correspond to the same molecule. In question 3, a chemical equation including O instead of O2 and another one H4O2 instead of H2O are proposed with two correct chemical equations, the students are asked which ones are wrong. A great number of students (35%) do not answer the first question. The students’ classification proposals rely mainly on two criteria: the state of matter (gas, liquid and solid) (17%) and the opposition between macroscopic and microscopic levels (24%). Thus the scientific name opposed to a common name does not seem to be a relevant tool used by the students (7%) to classify chemical species and mixtures. The students struggle to decode a chemical formula out of the context of a chemical equation (37% answer question 2 correctly) and fail to decode them in that context (17% succeed in answering question 3). These results confirm the need to offer teachers new didactical tools to develop the teaching of the language of chemistry. We intend to propose a teaching-learning sequence relying on historical texts used as didactical tools according to de Hosson’s view (de Hosson & Décamp, 2014)