Evaluating Students' Conceptual Understanding of Balanced Equations and Stoichiometric Ratios Using a Particulate Drawing

Abstract

A total of 156 students were asked to provide free-response balanced chemical equations for a classic multiple-choice particulate-drawing question first used by Nurrenbern and Pickering. The balanced equations and the number of students providing each equation are reported in this study. The most common student errors included a confusion between the concepts of subscripts and coefficients and including unreacted chemical species in the equation. Equations consistent with two of the five choices used in Nurrenbern and Pickering’s question appeared in this study, but none of the students provided balanced equations consistent with the other three distractors. Suggestions for better distractors are provided in this paper. The students were also asked to perform two stoichiometric calculations using the balanced equation they generated. These responses were evaluated to determine whether the students had a grasp of simple stoichiometric calculations and the reacting ratios of the two starting materials. Students who demonstrated confusion between subscripts and coefficients performed worse on the stoichiometric calculations than students who did not confuse these concepts. Most of the students who provided balanced equations including unreacted chemical species performed stoichiometric calculations using the incorrect reacting ratios of the starting materials listed in the equation.

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