Stepwise Approach to Hess’s Law Using Household Desiccants: A Laboratory Learning Program for High School Chemistry Courses

Abstract

This study focuses on designing a laboratory learning program for a high school chemistry course in which students could discover the fundamental principles of Hess's law via stepwise inquiry. By exploring the chemical properties of common desiccants, mainly those that were reactive in water, students were introduced to the exothermic reaction of CaO(s) with H 2 O(l) as a heating agent. Due to the difficulties associated with directly measuring the heat of reaction for CaO(s) with H 2 O(l), the heats of reaction for CaO(s) with HCl(aq) and Ca(OH) 2 (s) with HCl(aq) were measured. Students could find the most appropriate experimental procedures through discussion in each group and subsequently establish a protocol in the class. The heats of reaction determined by students' experiments closely corresponded to those calculated using the thermodynamic database. Using the experimental values obtained for the reactions of CaO(s) with HCl(aq) and Ca(OH) 2 (s) with HCl(aq), students could discover the relationship that existed among the heats of reaction for CaO(s) with H 2 O(l), CaO(s) with HCl(aq), and Ca(OH) 2 (s) with HCl(aq) by drawing an energy diagram and making the relevant thermochemical calculations.

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

“…The instructor then introduced the concept of solution equilibrium of Ca­(OH) 2 (Lesson 2). The students’ activities in Step 1 were almost identical to those used in the introductory part of the previously reported learning program that was aimed the discovery of the Hess’s law using the CaO–water reaction …”

“…The thermometric measurements were conducted by the students using a homemade calorimetric vessel and a thermocouple thermometer connected to a laptop PC for data acquisition (see Instructor Information in the Supporting Information). ,− Because the thermometric measurements are not subjected to calorimetric calculations in this learning program, the experimental setup can be simplified by using an ordinary coffee cup calorimeter and a digital thermometer. − Typical students’ results from the comparative thermometric measurements are shown in Figure . In Step 5, students incorporated prior knowledge acquired during learning Steps 1–4 to determine the chemical mechanism governing the exothermic reaction between heating agent B and water.…”

“…Many daily use materials incorporate various ingenious chemical ideas that can be applied to achieve optimal, purpose-driven performance levels. When a stepwise inquiry is successfully designed using these daily use materials and implemented in a school-based laboratory setting, students have numerous opportunities to integrate their knowledge base and prior understanding of chemical concepts. − These activities help students to process the new chemical phenomena through the introduction of new knowledge and concepts. Here, the active use of critical thinking skills and analytical development is promoted during the laboratory-based learning experience…”

“…They are also familiar household materials, excellent for engaging students during laboratory-based learning programs. − Laboratory-based learning programs focused on the redox reactions occurring in chemical hand warmers via iron oxidation reactions ,, and those which feature the microwave-assisted reduction of the iron oxides in its waste have been reported. A conventional heating pack based on CaO–water reactions was previously used to teach the chemical concepts governing Hess’s law …”

“…A conventional heating pack based on CaO−water reactions was previously used to teach the chemical concepts governing Hess's law. 3 This study focuses on using an alternative heating pack to study the reaction between a CaO−aluminum (Al) mixture and water, enabling more effective heating than its conventional CaO−water counterpart.…”