Difficulties of novice students in solving the final concentration value of a mixture of solutions

Abstract In this paper, we investigated and classified the answers of college freshmen when asked about “the final concentration value of a mixture of solutions ”. Prior to the explanation of the topic in class, a diagnostic questionnaire on “solutions” was presented to 532 first year students in the chemistry course at the University of Buenos Aires. The questionnaire consisted of three questions assessing the same concept: the calculation of the final concentration of a solution obtained mixing a concentrated and a dilute solution of the same solute. The format of the three questions was multiple choice answer with justification, but they differed in their chemical language style: chemical formulas, verbal-procedural, and visual languages were used. It was noted a trend to apply mathematical calculations, when chemical problems are addressed, even when such calculations are not necessary. Thus, obtaining a numerical result would be considered appropriate by the students, with no analysis of the significance of the value obtained. Nevertheless, question which uses visual language was answered correctly by a greater number of students. This would allow inferring that the use of this language brings students closer to a better understanding of the situation.