STEM Activities in Determining Stoichiometric Mole Ratios for

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STEM Activities in Determining Stoichiometric Mole Ratios for Secondary-School Chemistry Teaching Patcharee Chonkaew, Boonnak Sukhummek,*,† and Chatree Faikhamta‡ †

King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand Kasetsart University, Bangkok 10900, Thailand

‡

J. Chem. Educ. Downloaded from pubs.acs.org by UNIV OF SUSSEX on 04/30/19. For personal use only.

S Supporting Information *

ABSTRACT: This article provides teachers with a guideline on how to create a science, technology, engineering, and mathematics (STEM) hands-on environment and prepare a small lab kit for determining stoichiometric mole ratios of the reaction between hydrogen gas and oxygen gas for secondary-school students. This guideline will provide teachers with a low-cost, simple and rapid workstation allowing and encouraging small groups of students to gain hands-on experience. The small lab kit is developed based on the principle of green chemistry resulting in less chemical usage, less time consumption and less waste production. This article also provides related STEM activities to improve the engagements, aspirations and attitudes of students toward science and technology. These activities provide students with a chance to explore the stoichiometric mole ratio concepts and challenge them toward STEM. KEYWORDS: High School/Introductory Chemistry, Inorganic Chemistry, Interdisciplinary/Multidisciplinary, Hands-On Learning/Manipulatives, Problem Solving/Decision Making, Gases, Green Chemistry, Microscale Lab, Stoichiometry

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things.11,12 Chemistry requires an ability to link four levels of understanding: macroscopic, microscopic, symbolic, and process.13,14 In the school chemistry curriculum, the concept of stoichiometry is fundamental to understanding other related concepts, such as solution, kinetics, acids and bases, and chemical equilibrium. Many students, including first-year undergraduate students, have difficulties in understanding and solving related stoichiometric problems,15 especially when a reaction has more than one reactant. The students must determine the stoichiometric mole ratios related to all substances in the reaction. The stoichiometric mole ratio is very important in chemical calculations (e.g., calculations of theoretical yield, percent yield, and the quantities of mass and energy involved in the chemical reaction).16 In order to gain a deep conceptual understanding in chemistry, students should be provided with situations where lessons taught in the classroom are adaptable to or implemented with real-world situations.17 To solve any daily life problem, a single concept or principle is not sufficient.18 For science, technology, engineering, and mathematics (STEM), integration of different concepts and principles is normally involved to solve authentic problems. Students are exposed to different kinds of teaching methods to increase their learning skills, that is, questioning, experimenting, and cooperating.19 However, STEM in

INTRODUCTION Numerous studies show that students’ attitudes and aspirations toward science are developed during secondary school. Students who studied science during secondary school are more likely to continue their study by enrolling in science courses at a university. This may also lead the students to pursue a profession in science-related careers.1−3 Secondary education is regarded as an important stage for developing students’ interest and confidence in and utilization of science.4 Many studies have also confirmed that teachers are a crucial element in guaranteeing positive growth in student achievement.5−7 Teachers can promote students by providing various different teaching and learning approaches or activities in order to inspire and encourage them.8 A meaningful learning experience should offer a welcoming environment, encouragement, and collaboration.9 This allows students to strengthen their knowledge on the basis of prior knowledge and new discoveries. One of the main aspects promoting the relevance and utility of science to students is authentic and real-life situations.10 This creates opportunities for students to establish hypotheses, make decisions; solve problems; and perform complex, meaningful, and challenging tasks. Ordinarily, students are given some leading questions to answer. The students will then be given an assignment that requires the students to use the knowledge gained to present to the class.9 Chemistry is a fundamental science subject and is commonly described as a difficult subject by students. This is mainly because chemistry is a study of invisible and untouchable © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: November 30, 2018 Revised: April 1, 2019

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DOI: 10.1021/acs.jchemed.8b00985 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Activity

container was marked into six equal portions, as shown in Figure 2. Then, the body was fully filled with water to collect the hydrogen gas and oxygen gas produced. The hydrogen gas was produced from the reaction of magnesium-metal pieces with hydrochloric acid, which took place within a plastic bottle.

chemistry is relatively sparse, especially the on stoichiometry topic, which is indicated as a hard topic, and it seems unrelated to activities in everyday life. Hands-on activities certainly contribute not only to students’ scientific inquiry skills but also to their profound understanding of science. Successful miniaturized or small lab kits have been described in many articles.20−23 They are great tools that reduce the use of chemicals and energy, saving time and the environment.20 They can also reduce the levels of potential incidents or accidents that might occur. When compared with the traditional laboratory, the small lab kit can allow for smaller group sizes. Thus, more students will have a chance to take part in the experiment and develop higher-order thinking skills and conceptual understanding of the chemistry concepts. The hands-on small lab kit for determining the stoichiometric mole ratio of the oxidation of hydrogen gas by oxygen gas presented in this study is well suited for STEM teaching in every chemistry classroom, especially at the secondary-school level. It is a simple, safe, economical, and fun lab kit; thus, it is a fantastic method for educating students. The objectives of the hands-on activities are (1) to study the stoichiometric volume ratio of hydrogen gas and oxygen gas in the oxidation of hydrogen gas and (2) to construct a useful item powered by the energy created from the reaction of hydrogen gas and oxygen gas.

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Mg(s) + 2HCl(aq) → MgCl 2(aq) + H 2(g)

(1)

The oxygen gas was produced from the reaction of yeast with hydrogen peroxide that takes place within another plastic bottle. yeast 2H 2O2 (aq) ⎯⎯⎯⎯⎯⎯→ 2H 2O(l) + O2 (g)

(2)

To collect a gas mixture of hydrogen gas and oxygen gas at various volume ratios, the body of the plastic container was fully filled with water. It was later fitted with the tips of the gasproducing bottles (i.e., the hydrogen-gas bottle and the oxygen-gas bottle) in no particular order to allow the gases to replace the water through a hollow stalk until the desired amount of gas was obtained. The volume ratios of hydrogen gas−oxygen gas were 0:6, 1:5, 2:4, 3:3, 4:2, 5:1, and 6:0. After the plastic container was finished being filled, the cap was closed, and the gas containers were kept for further use. Part I: Stoichiometric Volume Ratio of Hydrogen Gas and Oxygen Gas

EXPERIMENTAL SECTION

Students were asked to determine the limiting reactant and the stoichiometric volume ratio of hydrogen gas and oxygen gas. Energy created from the oxidation reaction of hydrogen gas by oxygen gas was used to propel a gas-mixture container in a rocketlike manner. The travel distance of the gas-mixture container and the period of time it was airborne were used to verify the extent of the reaction of hydrogen gas and oxygen gas. Each gas-mixture container had a different volume ratio of hydrogen gas and oxygen gas, and the containers were launched at a fixed projected angle of 45°, as shown in Figure 3. A piezo sparker was used to initiate the oxidation reaction of the hydrogen gas. The horizontal displacement and the period of time that each container was airborne were measured, and the average values of three trials were recorded.

Chemicals and Materials

Chemicals and materials used in the preparation of the handson small lab kit for determining the stoichiometric volume ratio of the exothermic reaction of hydrogen gas and oxygen gas are shown in Figure 1.

Part II: Relationship of the Projected Angle and the Horizontal Displacement

Students were assigned to determine the relationship of the projected angle with the horizontal displacement by varying the projected angles and recording the horizontal displacements that occurred. For this section, the gas-mixture volume ratio of hydrogen gas and oxygen gas was fixed at 4:2, whereas the projected angle was varied (0, 30, 45, and 60°). A new set of gas-mixture containers was produced. The horizontal displacements corresponding to the projected angles were then recorded.

Figure 1. Chemicals and materials used in the preparation of the hands-on small lab kit for the determination of the stoichiometric ratio of the reaction of hydrogen gas and oxygen gas.

It is worth noting that the student worksheet and instructor handout are provided separately in the Supporting Information.

Part III: Construction of a Useful Item Powered by the Energy Created from the Reaction of Hydrogen Gas and Oxygen Gas

Procedure

Preparation of Gases. Preparation of hydrogen gas and oxygen gas and the main procedure were developed from Flinn Scientific Inc.24 The gases were collected by the waterdisplacement method. First, the cap from a clean, empty, clear, and colorless rodlike plastic container was removed. The body of the plastic

After the stoichiometric volume ratio and the appropriate projected angle were obtained, the teacher asked each group of students to create a useful item. The students were instructed to base their creation on the knowledge and experience gained on the stoichiometry concept. B

DOI: 10.1021/acs.jchemed.8b00985 J. Chem. Educ. XXXX, XXX, XXX−XXX

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Figure 2. Preparation of hydrogen-gas and oxygen-gas collection. (a) Rodlike plastic container with marked lines. (b) Filling water into the marked plastic container. (c) Water replaced with produced O2 gas.

Figure 3. Equipment used to launch the gas-mixture containers that contained various volume ratios of hydrogen gas and oxygen gas.

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HAZARDS The use of personal protective equipment is essential. Most importantly, students should wear safety goggles at all times throughout the class activities. Hydrochloric acid is a hazardous liquid and can adversely affect human health or even be fatal in severe cases. Avoid contact with all chemical reagents and dispose of waste solutions into appropriate waste containers.

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Table 1. Relationship of the Volume Ratio of H2 and O2 Gases, Time, and the Horizontal Displacementa

RESULTS

Volume Ratio of H2−O2

Average Time (s)

Average Displacement (m)

0:6 1:5 2:4 3:3 4:2 5:1 6:0

N/Ab N/A N/A 0.97 ± 0.056 1.03 ± 0.017 0.81 ± 0.079 0.44 ± 0.061

0.000 0.000 0.000 0.523 ± 0.0217 0.558 ± 0.0615 0.384 ± 0.0234 0.247 ± 0.0404

a Recorded at a fixed shooting angle of 45°. bN/A indicates propulsion of the gas container did not occur.

Stoichiometric Volume Ratio of Hydrogen Gas and Oxygen Gas

To determine the stoichiometric volume ratio of hydrogen gas and oxygen gas, each gas-mixture container, prepared in the ratios 0:6, 1:5, 2:4, 3:3, 4:2, 5:1, and 6:0, was launched by using a gas lighter at a fixed projected angle of 45°. The average horizontal displacements were recorded, as shown in Table 1. The extent of the reaction could be quantified by using two aspects. The first aspect was visually the distance the gasmixture container was propelled. As the results in Table 1 show, the ratio of H2 and O2 gases that allowed the container to move with the longest horizontal displacement was 4:2 or the simplified ratio of 2:1. On the other hand, the gas containers of the first three ratios (0:6, 1:5, and 2:4) did not launch because of a lack of sufficient energy created. Thus, the volume ratio of H2−O2 at 2:1 delivered a complete reaction of H2 and O2 gases, which implied that there was no remaining substance and that the reaction produced the highest amount of energy. The second aspect was the period of time the gas container was airborne. The result revealed that the longest

period of time the gas container was airborne was also at the volume ratio of 4:2. In addition, on the basis of Gay-Lussac’s law (“Volume ratio of the reactant and the product gases is maintained and can be expressed in simple whole numbers”) and Avogadro’s law (“Equal volumes of all gases, at the same temperature and pressure, have the same numbers of molecules”25) and referring to the highest airborne time and horizontal distance obtained at the volume ratio of H2 gas and O2 gas of 4:2 (the smallest volume ratio was 2:1), it was implied that two molecules of hydrogen gas reacted completely with one molecule of oxygen gas. Thus, the balanced oxidation reaction of hydrogen gas could be written as 2H2(g) + O2(g) → 2H2O(g) + energy. Relationship of the Projected Angle and the Horizontal Displacement

The balanced stoichiometric mole ratio of H2 and O2 gases of 2:1 from the result of the first part was used to investigate the relationship of the projected angle with the horizontal C

DOI: 10.1021/acs.jchemed.8b00985 J. Chem. Educ. XXXX, XXX, XXX−XXX

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displacement. The gas-mixture containers were launched at the various angles (0, 30, 45, and 60°), and the results are shown in Table 2. Table 2. Relationship between the Projected Angle and the Horizontal Displacement Projected Angle (°) 0 30 45 60

Average Time (s) 0.51 0.97 1.29 1.01

± ± ± ±

0.045 0.026 0.042 0.172

Average Displacement (m) 0.333 0.420 0.516 0.393

± ± ± ±

0.0189 0.0034 0.0085 0.0134

Figure 5. Automatic sending tool.

Table 2 shows that the longest displacement and airborne time were 0.516 m and 1.29 s, respectively, for which the gasmixture container was launched at 45°. This observation was proved by projectile-motion theory.26 The students had learnt this theory last year in their grade 10 physics class. This activity could act as a tool for evaluating students’ knowledge retention of the projectile concept. However, for a first-time experience, students could explore and build their own projectile knowledge. In this particular motion, the effect of air resistance was ignored.

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CONCLUSIONS AND DISCUSSION

A small lab kit for determining the stoichiometric mole ratio of hydrogen gas and oxygen gas has been developed and successfully implemented as a teaching tool for promoting students’ engagement, aspirations, and positive attitudes toward STEM. These hands-on activities integrated with inquiry-based learning can have an important influence on students’ understanding, higher-order thinking skills, and performance.28 With the implementation of the small lab kit, a large number of students can perform the experiment on their own and develop their own thinking processes as they interact with each other and the teacher while creating their useful item. When students enjoy the learning activities, they are eager to learn and achieve higher-order cognition. All the students were very excited from the first time they saw the rocketlike gas container launching and traveling with a popping sound. Consequently, everyone wanted to have a turn. The class environment was marvelous. Most of the students enjoyed and engaged with these activities. They were more curious and more courageous in expressing their ideas than they had been before. One of the students’ reflective journals stated, “Learning activity helps me to think scientifically and challenges my ideas.” In a random interview, another student said, “Activity brought by the teacher is fun and new and it is not written in any part of the textbook. Thus, I do not get bored of learning.” Such expressions clearly show their positive attitudes toward science improvement after participating in the STEM activities. Teachers are also a powerful influence on students’ perceptions on their knowledge, including their knowledge of STEM. Teachers should design and provide opportunities for students to learn how to manage things, cope with challenging situations, and apply what they have learned to real-world applications. Real-life-based learning activities help students to realize that theories and fundamental science knowledge are crucial in life, affecting the skills and attitudes of students in relation to STEM. The teachers should also have a deep understanding of a particular field so that they can impart the concepts and procedures through various perspectives to the students. Promptly guiding, suggesting, and supporting students’ learning are the key characteristics of successful teachers. In addition, teachers should play the role of a facilitator, helping students become active learners who actively search for related knowledge learned in school to resolve the real-life problems assigned.

Construction of a Useful Item Powered by the Energy Created from the Reaction of Hydrogen Gas and Oxygen Gas

After completing the previous two experiments, the teachers asked students to create a useful item for making life easier and more convenient by using their knowledge of the stoichiometry concept and experiences gained from the past experiments. One of the useful items designed by the students was an automatic tool for sending a rope to fire fighters. A drawing is shown in Figure 4, and the real sending tool is exhibited in

Figure 4. Drawing of an automatic tool sending rope to fire fighters.

Figure 5. Other types of useful objects, for example, tools for shooting fishing,27 for sending a life buoy to a drowning person, and for shooting a ping-pond ball, were also proposed. Even though the students tried their hardest to build efficient and useful items, not all groups were successful. For example, for the case of sending the life buoy, the buoy did not go far because of its heavy weight. Nonetheless, the students expressed their understanding of how to integrate and apply conceptual knowledge and procedural skills with a complex problem. D

DOI: 10.1021/acs.jchemed.8b00985 J. Chem. Educ. XXXX, XXX, XXX−XXX

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00985.

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Student worksheet and instructor handout (PDF, DOCX)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Boonnak Sukhummek: 0000-0002-5012-9836 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The success of this study was supported by many people and organizations. The authors greatly appreciate the financial support provided by the Institute for the Promotion of Teaching Science and Technology (IPST) and the Project for the Promotion of Talented Science and Mathematics Teacher (PSMT).

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DOI: 10.1021/acs.jchemed.8b00985 J. Chem. Educ. XXXX, XXX, XXX−XXX