Discovering the Chemical Mechanism of Common Heating Agents: A Stepwise Inquiry with Student-Designed Experiments in a High School Laboratory Course

Abstract

A newly developed laboratory learning program for high school chemistry courses is discussed, in which students discover the chemical mechanism governing exothermic phenomena during the reaction between a heating agent, namely, calcium oxide (CaO)−aluminum (Al) mixture, and water. Based on prior knowledge of simple heating agents such as CaO, the students were able to accurately identify the component chemical reactions in the CaO−Al mixture and water system using three pairs of comparable thermometric measurements arranged in a stepwise manner. In each step, the students designed the comparative experiments for each student group through logical thinking and argumentation to obtain relevant and reliable results. Active interpretation of the results enabled each student to learn the chemical phenomena inherent in the observed reactions, and their understanding was deepened through evidence-based argumentation and debate. Finally, students in each group proposed an overall chemical mechanism governing the reaction between the CaO−Al mixture and water by consolidating the knowledge acquired during the previous inquiry steps. The proposed chemical mechanism was fine-tuned through group presentations, followed by question and answer sessions. The 6-h evidence-driven activity provided numerous opportunities for experiencing the multifaceted aspects of the scientific inquiry process.

Dissolution of Calcium Hydroxide in Water: A Guided Inquiry in University and High School Chemistry Laboratories

“…Previously reported laboratory activities of the heat of reaction of CaO(s) with water and the mechanism of exothermic reaction in a CaO(s)–Al(s)–water system completely cover the fundamentals of Ca­(OH) 2 (s) and Ca­(OH) 2 (aq). Furthermore, the Ca­(OH) 2 (s) solution equilibrium may be introduced as one of the component processes in the exothermic phenomenon of the CaO(s)–Al(s)–water system used as a commercially available heating agent . It is acknowledged that the educational practices according to Plan A at Hiroshima University were carried out after students participated in laboratory inquiries on the heating agents of CaO(s)–water and CaO(s)–Al(s)–water systems.…”

“…Regardless of the subsequent structure and flow of student inquiry, the fundamental chemical characteristics of Ca-(OH) 2 (s) and Ca(OH) 2 (aq) are introduced, including the solubility of Ca(OH) 2 (s) in water and the basic property of Ca(OH) 2 saturated solution. Previously reported laboratory activities of the heat of reaction of CaO(s) with water 21 and the mechanism of exothermic reaction in a CaO(s)−Al(s)− water system 22 completely cover the fundamentals of Ca-(OH) 2 (s) and Ca(OH) 2 (aq). Furthermore, the Ca(OH) 2 (s) solution equilibrium may be introduced as one of the component processes in the exothermic phenomenon of the CaO(s)−Al(s)−water system used as a commercially available heating agent.…”

“…Furthermore, the Ca(OH) 2 (s) solution equilibrium may be introduced as one of the component processes in the exothermic phenomenon of the CaO(s)−Al(s)−water system used as a commercially available heating agent. 22 It is acknowledged that the educational practices according to Plan A at Hiroshima University were carried out after students participated in laboratory inquiries on the heating agents of CaO(s)−water and CaO(s)−Al(s)− water systems. When the laboratory activity presented in this laboratory experiment is employed independently of the previously reported laboratory activities, students' knowledge of the decrease in Ca(OH) 2 (s) solubility with increasing temperature can be used to introduce students to the solution equilibrium of Ca(OH) 2 (s).…”

“…21 A progressive investigation employing student-designed experiments can also reveal the chemical mechanism of the heating agent in the CaO−Al−water system. 22 These stories related to chemistry of the CaO−Ca(OH) 2 −water system can serve as a good introduction to the physical chemistry of the Ca(OH) 2 (s) dissolution in water. Therefore, the second goal of this work was to create laboratory learning programs suited for university and high school chemistry courses by integrating laboratory inquiries focusing on the thermochemistry in the Ca(OH) 2 − water system and Ca(OH) 2 solution equilibrium.…”

“…The Ca­(OH) 2 solution equilibrium is a key phenomenon in the reactions of common heating (exothermic) agents in the CaO–water and CaO–Al–water systems. , We recently reported a laboratory learning program in high school chemistry courses that focuses on thermochemistry using the heating agent of the CaO–water system . A progressive investigation employing student-designed experiments can also reveal the chemical mechanism of the heating agent in the CaO–Al–water system . These stories related to chemistry of the CaO–Ca­(OH) 2 –water system can serve as a good introduction to the physical chemistry of the Ca­(OH) 2 (s) dissolution in water.…”