The effect of a visually-based intervention on students' misconceptions related to solutions, solubility, and saturation in a core materials course

Students' understanding of the concepts of solutions, solubility and saturation has been widely studied, and findings have revealed that students come to a course with misconceptions; most of which have not changed significantly since earlier instruction. One study revealed that, while the majority of students defined solution and solubility concepts correctly, only a small fraction matched these definitions with the correct pictorial representations. Other studies have also shown poor student performance on both pre and post topictest quizzes. The most common misconception from the literature showed that students often mistake a saturated solution for a supersaturated solution. This usually occurs when they are shown a beaker containing a solution with undissolved solute at the bottom. Likewise, a smaller percentage of students also assumes that the same solution is unsaturated because the precipitates have not "mixed" in. The research question posed in this paper is "what is the effect of a visually-based instructional intervention on students' misconceptions related to solutions, solubility and saturation". Data from this 2012 study were compared with that of a 2011 class when the concepts were taught using only phase diagram graphs. The visually-based intervention was a two-part worksheet activity. It was carried out at the beginning of the topic of phase diagrams in an introductory materials science course. In the first part, sugar was added gradually to a beaker containing water until it reached saturation and then retained some undissolved sugar at the bottom. The second part showed a saturated solution that was allowed to evaporate undisturbed. Students worked in teams to discuss the solutions and construct their own meaning of the concepts. A two-part pre and post topic quiz was given before and after phase diagram instruction. The first part showed three beakers, each containing supersaturated, saturated and unsaturated solutions for which students had to choose which one of the three types of solutions each beaker contained. The second part of the quiz asked students to explain their reasoning. Percentages of correct answers were calculated and the scores were normalized using the Hake Gain method. Analysis of pre and post test results showed that students performed better in 2012 than in 2011. The most common misconceptions remained the same. In particular, students still chose the saturated solution as being supersaturated, although the percentage that did was smaller in 2012. After instruction, an average of 25% of the explanations were correct in 2011 compared with 42% in 2012. Post test analysis of students' explanations showed that the reason most incorrect answers were due to a lack of understanding of the role of solubility limit of solutes in solution.