High school students and students in the first years
of college
have difficulties in understanding the topic of stoichiometry and,
in particular, the concept of limiting reactant. Proposals aimed at
overcoming these learning obstacles tend to focus on analogies, and
there are few sequences that approach teaching from an experimental
perspective. Those that do it usually involve specific reactions whose
reagents are not easily obtained or require special equipment. In
this article, an experimental activity was designed to introduce the
concept of limiting reactant with nonhazardous, inexpensive, and readily
available materials in combination with an innovative visual and graphic
representational approach. It was implemented with three groups of
16–17 years old students (N = 74) with some
previous knowledge (acid and base reactions, indicators, and slight
experience in handling laboratory material). From their own observations
and reasoning and without the need to go through analogical mediation,
it was possible to satisfactorily arrive at the concept of limiting
reactant. Subsequently, the proposal was adapted for students with
no prior knowledge, and it was implemented with three groups of 9–12-year-olds
(N = 27) in an informal teaching environment with
similar results. This intervention could potentially help high school
students better understand the concept of limiting reagents and overcome
future learning obstacles in relation to other chemical phenomena
that rely on this concept.