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.