We study how to capitalize on learning titration in order to improve the understanding of chemical change, chemical reaction and stoichiometry by secondary school students. According to the "Ingenierie Didactique" framework, the analyses of students' misrepresentations, of the effect of the usual teaching are needed in order to elaborate fruitful teaching strategies. A first study about the notion of limiting reactant understanding revealed two conceptions. "Both reactants are totally converted at the end of the chemical change" whatever the proportions seems to be the most common one. This would be in competition with the conception "only one reactant is totally converted" when a solid is one of the reactants. A second study deals with titrations misrepresentations. We show that many students think that no chemical change occurs before the equivalence point and one occurs suddenly at the equivalence point whatever the kind of titration. A third study about the effects of variables show the little effect of the "type of titration" unlike the effect of the "type of questions" on the last representation. And we note that conductance variation is more favourable than pH variation to make students consider the evolution of the chemical system. In conclusion, we give some suggestions for titration teaching.
learning about titrations : misrepresentations of secondary school students and variables effects