Cognitive strategies used by chemistry students to solve volumetric analysis problems

The study investigated the strategies used by 47 high school students to solve volumetric analysis problems in chemistry. Using the talking-aloud technique, the students were required to calculate the concentration of hydrochloric acid used in a titration with NaOH after having performed the titration themselves. Students were met individually and their verbalization audiotaped. After making this calculation, each student was asked to use the same data to predict the concentration of acid in three situations involving different mole ratios. It was found that two main strategies, Formula Approach and Proportional Approach with their variants, were employed by the students during the problem solving process. The Formula Approach was found to be used mainly by the students in the high ability group while students in the low ability group used the Proportional Approach. It was also found that problems involving 2:1 stoichiometric ratios presented a number of conceptual problems to the students. These conceptual problems were found to be related to their inability to write balanced equations or write correct formulas, focusing on only the strength of acid, inability to use the mole ratios in the calulations and deriving the mole ratios from the formulas of reactants.     

Development and validation of a path analytic model of students' performance in chemistry

This article reports the development and validation of an integrated model of performance on a chemical concept - volumetric analysis. From the chemical literature a path-analytic model of performance on volumetric analysis calculation was postulated based on studies utilizing the proportional reasoning schema of Piaget and the Cumulative learning theory of Gagne. This integrated model hypothesized some relationships among the variables: direct proportional reasoning, inverse proportional reasoning, prerequisite concepts (content) and performance on volumetric analysis calculations. This model was postulated for the two groups of students involved in the study - that is those who use algorithms with understanding and those who use algorithms without understanding. Two hundred and sixty-five grade twelve chemistry students in eight schools (14 classes) in the lower mainland of British Columbia, Canada participated fully in the study. With the exception of the test on volumetric analysis calculations all the other tests were administered prior to the teaching of the unit on volumetric analysis. The results of the study indicate that for subjects using algorithms without understanding, their performance on VA problems is not influenced by proportional reasoning strategies while for those who use algorithms with understanding, their performance is influenced by proportional reasoning strategies.