Students' dilemmas in reaction stoichiometry problem solving: deducing the limiting reagent in chemical reactions

A qualitative case study was conducted to investigate the understanding of the limiting reagent concept and the strategies used by five Year 11 students when solving four reaction stoichiometry problems. Students' written problem-solving strategies were studied using the think-aloud protocol during problem-solving, and retrospective verbalisations after each activity. Contrary to several findings reported in the research literature, the two high-achieving students in the study tended to rely on the use of a memorised formula to deduce the limiting reagent, by comparing the actual mole ratio of the reactants with the stoichiometric mole ratio. The other three average-achieving students, however, generally deduced the limiting reagent from first principles, using the stoichiometry of the balanced chemical equation. Overall, the students displayed limited confidence during problem-solving to determine the limiting reagent and to perform related computations.