Portable syringe kit demonstration of gas generating reactions for upper secondary school chemistry

1.1 Conceptual understanding of chemical reaction rate

There are many studies on students’ conceptions of the topic of chemical reaction rate or chemical kinetics. For example, Çalik and his colleagues (Çalik et al., 2010) examined previous studies and identified problems encountered in learning the concept of chemical reaction rate. Some of these problems are (1) inability to define the rate of reaction, (2) misunderstanding, misapplying, or misinterpreting of the relationship between the rate of reaction and its influencing factors, and (3) lack of understanding of how activation energy and enthalpy relate the rate of reaction. They also investigated the effects of conceptual change pedagogy on Students’ conceptions. They found that the conceptual change pedagogy intervention helped the students to notice and correct their alternative conceptions. They suggested that combining various conceptual change methods may be more effective in decreasing student alternative conceptions.

They also explored the alternative conceptions of chemical reaction rates generated by Turkish chemistry teachers and students (grade 11). They found that chemistry teachers and students tended to accommodate similar alternative conceptions, which may be transmitted from the chemistry teachers. Examples of some alternative conceptions include: (1) lack of understanding of how enthalpy affected the rate of reaction and reaction mechanism of the reaction, and (2) misunderstanding/misapplying of the relationship between temperature or concentration and the rate of reaction (Çalik et al., 2010).

The following example concerns Thai students’ learning of chemical kinetics, which was investigated by Chairam and his colleagues (Chairam et al., 2009). It was reported that chemical kinetics is an essential concept in introductory chemistry. In Thailand, high school and undergraduate students typically begin learning chemical kinetics, focusing on qualitative aspects. Students are usually introduced to reaction rates and the factors that influence them. The study also explored the impact of inquiry-based learning activities, where first-year undergraduate science students at a public university in Thailand were asked to design and conduct an experiment investigating acid-base reactions. The results indicated that this more engaging hands-on teaching helped students build a strong conceptual understanding of chemical kinetics. A study by Supasorn and colleagues (Supasorn et al., 2022) examined grade 11 students’ understanding of reaction rates before and after they participated in the small-scale syringe-vial experiment (SSVE) and used the AR interactive Particulate-level Visualization (ARiPV) within the 5E inquiry-based learning framework at a typical upper secondary school in Ubon Ratchathani, Thailand. Initially, most students fell into partial understanding with specific misconceptions (PMU), with no students achieving good understanding (GU). Following the intervention, most students improved to partial understanding (PU), with no students remaining in the no understanding (NU) category. This study demonstrated that the integrated approach helped students better understand reaction rates.

Based on the literature review above, inquiry activities have proven effective in supporting students’ conceptual understanding of chemical kinetics. However, many upper secondary schools in Thailand encounter severe limitations in implementing conventional chemistry experiments. These limitations include insufficient equipment and chemicals, no toxic waste management system, time consumption of experimental activities, and inadequate skilled instructors for preparation and teaching experiments (Khattiyavong et al., 2014). du Toit & du Toit (2025) state that understanding chemistry is crucial for future solutions, so chemistry should be more accessible to all students. They suggest that micro-scale or small-scale chemistry is one of the effective ways to make chemistry more accessible. As a result, a portable syringe kit demonstrating the chemical kinetics of gas-generating reactions was developed to minimize the stated limitations (Supasorn et al., 2021; Supasorn et al., 2022). In addition, the kit must be repeatable, easy to set up, demonstrate, clean, safe to perform, and easy to observe changes. Please note that this article mainly discusses developing and validating the experimental kit as a demonstration tool for qualitative comparison among various gas-generating reactions.

1.2 Gas generating reactions

There are many reactions involving gas generation. Some of those are shown below (Herr & Cunningham, 1999).

However, this article only studies the reactions producing hydrogen (H₂), carbon dioxide (CO₂), and acetylene (C₂H₂) gases. In other words, the H₂ gas was generated from the reactions of sodium metal (Na) with distilled water (H₂O) and magnesium (Mg) ribbon or zinc metal (Zn) with various acids (Herr & Cunningham, 1999). The CO₂ gas was generated from the reactions of bicarbonate (HCO₃ ⁻) or carbonate salts (CO₃ ²⁻) with various acids (Chairam et al., 2009). The C₂H₂ gas was generated from calcium carbide (CaC₂) reactions with distilled water (Chang & Overby, 2019). The reaction equations for the above gas-generating reaction are shown in Figure 1.

Figure 1:

H₂, CO₂, and C₂H₂ gas generating reactions (Chang et al., 2019).

Typically, water displacement in a glass burette or a graduated cylinder can be used as the standard traditional method for measuring the volume of gas generated from any reaction (Chairam et al., 2009). As shown in Figure 2, the syringe was used as an alternative method for measuring the volume of gas in this experimental kit.

Figure 2:

Gas volume determination by water displacement, (a) apparatus setup, (b) procedure for gas volume determination.

1.3 Chemistry in the syringe

There are many studies investigating chemical reactions via syringe systems. For example, a series of small-scale gas experiments aimed at enhancing safety and engagement in chemical education. Developed by Obendrauf (2006), these experiments minimize chemical hazards and waste while allowing students to witness visually striking reactions. The experiments cover gas production (e.g., chlorine, hydrogen, acetylene) and reactions between gases, such as the photolytic reaction of hydrogen and chlorine, which can be ignited by light, and the explosive mixture of hydrogen and oxygen. The experiments are designed to appeal to students’ emotions and curiosity, making theoretical concepts more memorable through visually appealing or intense demonstrations. Another example Ng et al. (2020) provided introduced a safe, engaging method for conducting gas-generating experiments in educational settings using disposable plastic syringes, where hydrochloric acid reacts with calcium carbonate to produce CO₂ gas. The generated gas is measured by channeling it into an inverted burette for accurate volume recording. This technique minimizes exposure to hazardous chemicals and teaches fundamental concepts such as reaction rates and gas measurement, emphasizing laboratory safety and handling practices for young science students​. The last example is a portable, low-cost syringe-vial kit designed by Supasorn et al. (2021) to demonstrate chemical reaction rates through gas-generating reactions, specifically CO₂ gas generation from sodium bicarbonate and acid. The setup consists of a syringe, vial, and 3-way stopcock, allowing easy real-time observation of gas production and reaction rates. Tested in high school classes, the kit was shown to improve student understanding of reaction rates through hands-on, inquiry-based learning activities. The kit’s portability, simplicity, and safety make it ideal for educational use in diverse classroom settings​.

Building on the reviewed literature, we introduce a portable syringe kit to demonstrate gas-generating reactions in upper secondary school chemistry easily. This kit addresses several common experimental challenges, such as limited chemical supplies, a lack of advanced equipment, and time constraints. It provides a simple, effective way to illustrate key concepts like chemical reactions and reaction rates.

2.1 Treatment tool: portable syringe kit of gas generating reaction

This study used the portable syringe kit to demonstrate a gas-generating reaction as its treatment tool. This kit was adapted from the workshop entitled “Enjoy Chemistry Experiments with Syringe: Use syringes and 3-way cocks to carry out small-scale experiments” provided by Han & Kim (2013) at the 2013 ISMTEC organized by the Institute for the Promotion of Teaching Science and Technology (IPST) in Thailand, and adapted from the study of Nilsson & Niedderer (2012) in which they simulated that “chemical reaction between sodium and water takes place, and hydrogen gas is formed, in which the volume of the formed hydrogen gas can be determined by leading the gas into a syringe.” The idea of how to determine the volume of the generated gas was applied from the small-scale syringe-vial experiment (SSVE) on the rate of CO₂ gas-generated reactions previously developed by our team (Supasorn et al., 2021; Supasorn et al., 2022). The kit was also designed based on Green Chemistry principles, which include reducing the amounts of chemicals used, toxic chemicals, and generated wastes (Poliakoff & Licence, 2007). Details of the kit are as follows.

2.1.3 Equipment and apparatus

This setup involved two large and one small syringe, a 3-way stopcock, a needle, and chemical and solution containers. Luer-lock-tip syringes are preferred for tight connection (see Figure 3a).

Figure 3:

The syringe kit demonstration, (a) preparing chemicals and equipment, (b) preparing syringe kit, (c) transferring chemicals into syringes, and connecting syringe kit using 3-way connector.

2.1.4 General procedure

Prepare all chemicals, solutions, syringes, a 3-way stopcock or connector, and equipment as shown in Figure 3a and b. In the case of Na, it should be cleaned before use, and all the rest of the Na metal should be soaked in oil to prevent any unexpected ignition. Teacher or expert demonstration is advised for the reaction of Na and water. To demonstrate such a reaction, the solid and liquid reactants are placed in syringes A and B, while distilled water is placed in syringe C as a gas filter (see Figure 3c).

Connect these three syringes by using a 3-way stopcock, in which syringes A, B, and C are in the lower, horizontal, and upper positions, and then push the plunger of syringe B to transfer liquid reactant to react with solid reactant in syringe A (ensure that syringe A connected to syringe B, but C) as shown in Figure 4a. Then, observe the reaction progress, temperature change (endothermic or exothermic), and color change of the reaction mixture, as shown in Figure 4b. After the reaction is complete, push the plunger of syringe A to collect the gas in syringe C, remove all liquid from syringe A, and observe the generated gas volume. Please ensure that syringe A connects to syringe C, but B. Remove syringe C from the 3-way stopcock and put a needle instead. Push the plunger of syringe C to transfer the generated gas through the needle to test the gas. Ignition and flammability were applied for testing H₂ and C₂H₂ gasses (see Figure 4c), while turbidity of lime water (Ca(OH)₂) solution was used for testing CO₂ gas.

Figure 4:

The syringe kit demonstration, (a) assembly of the kit, (b) initiating of the reaction, and (c) ignition test of C₂H₂ gas generated from the reaction.

Three experts, one chemistry professor, and two chemistry education professors, validated this experimental kit. Any suggestions from the experts were considered to improve its effectiveness and usability. Please note that some reactions may produce heat, react very fast, and produce high pressure. These can cause the syringes to disconnect or push the plungers off the syringes. As a result, please proceed with caution and hold all syringes and plungers tightly.

2.2 Data collecting tool

This study used a conceptual test of chemical reaction rate as one of its two data-gathering instruments. The test contained 20 multiple-choice questions regarding chemical reaction rate, including three topics: the definition of reaction rate (questions 1–6), energy and reaction progress (questions 7–11), and factors influencing rate (questions 12–20). Please note that all research materials were written in Thai, and classes were taught in Thai. This article’s samples were all translated into English.

2.3 Participants

The participants of this study were 33 grade-11 students in one regular classroom from a large high school in the Thailand province of Ubon Ratchathani. With the previous agreement of the school principal and the chemistry instructor, in the 2nd semester of the academic year 2020 (November 2020 to February 2021), all participants signed informed consent forms and approved the study’s report and publishing to utilize their conceptual test data anonymously.

2.4 Implementation of portable syringe kit demonstration on chemical reaction rate

During the chemical reaction rate topic, the pre-conceptual test on chemical reaction rate took students 30 min to complete before the implementation, also called the pretest. Following that, a group of three to four students engaged in three 2-h inquiry-based learning activities using a portable syringe kit demonstration to investigate chemical reaction rate as follows: (1) demonstrations of H₂ gas generating reactions, (2) demonstrations of CO₂ and C₂H₂ gas generating reactions, and (3) factors influencing the rate of gas generating reactions. These activities were performed in a typical classroom environment. The 5E inquiry learning cycle provided the foundation for each initially created by Bybee (2014; as cited in Joswick & Hulings, 2024). In each 5E inquiry learning activity, the students were engaged with a scientifically-oriented question regarding chemical reaction rate (E1: Engagement step) and then explored data by performing a portable syringe kit demonstration of a generating reaction (E2: Exploration step). Next, they formulate explanations based on their experimental data (E3: Explanation step) and then relate or connect these explanations to principles and other scenarios involving reaction rates (E4: Elaboration step). Finally, their understanding was assessed through discussions, questions, and answers in both group and class settings (E5: Evaluation step). Finally, the post-conceptual test on chemical reaction rate took students 30 min to complete after the implementation, also called the post-test (identical to the pre-test but with the choices rearranged).

3.1 Experimental results of the portable syringe kit demonstration

The variety of H₂, CO_2, and C₂H₂ gas-generating reactions were observed using this syringe demonstration; please find the chemical equations for each gas in Figure 1. The % yields of gas products from the small-scale reactions using the syringe kit were in the range of 76–86, slightly lower than those of the conventional scale reactions (82–93). Furthermore, investigations of chemical reaction rates using the small-scale syringe kit could be completed within 6 min. In contrast, those using the conventional scale and water displacement method could take up to 25 min. For the H₂ gas-generating reactions (see Table 1), the following reactions were compared to demonstrate some effects on the reactions of Na and Mg with water and acids. Reactions No.1.1 and No.1.2 demonstrate that Na is more reactive than Mg as it can rapidly react with water, while reactions No.1.2 and No.1.3 demonstrate that Mg reacts with acid but water. Reactions No.1.3 and No.1.4 demonstrate that the reaction of monoprotic HCl acid and Mg produces less H₂ gas than diprotic H₂SO₄ acid, while reactions No.1.3 and No.1.5, strong HCl acids, react with Mg more rapidly than weak CH₃COOH acid. In addition, reactions No.1.3 and No.1.6 also demonstrate that increasing acid concentration increases the reaction rate. In addition, the appearance of pink color and the warming of the reaction mixture in syringe A indicates that the reaction mixture is basic and exothermic. The H₂ gas can be tested using ignition, and rarely visible yellow or orange flame can be observed.

For the CO₂ gas-generating reactions (see Table 2), reactions No.2.1 and No.2.2 demonstrate that NaHCO₃ reacts with acid slower than Na₂CO_3, resulting in less gas product, while reactions No.2.3 and No.2.2 demonstrate that increasing concentration of acid increases the volume of gas product. The CO₂ gas can be tested using turbidity of lime water. For the quantitative experiment to investigate the rate of CO₂-generating reaction and factors influencing the rate, please study supplementary materials.

For the C₂H₂ gas-generating reactions (see Table 3), reactions No.3.1 and No.3.2 demonstrate that increasing the amount of CaC₂ increases the volume of the gas product. In contrast, reactions No.3.2 and No.3.3 demonstrate that increasing the volume of water may not increase the reaction product since CaC₂ is a limited reagent of this reaction. The C₂H₂ gas can be tested using combustion in which the flame is very bright.

3.2 Students’ conceptual test score of chemical reaction rate

To verify the success of implementing the activity using the portable syringe kit demonstration of gas-generating reaction whereby students’ understanding of the concepts of chemical reaction rate could be improved, the volunteered participants were required to complete a conceptual test before and after experimenting, respectively called pre- and post-conceptual understanding tests. Before the undertaking of the experiment, the student’s average percentages of the pre-test scores for the concepts of the definition of reaction rate, energy, and reaction progress, factors influencing rate, and total were 41.92, 27.88, 31.99, and 33.94, respectively (see Table 4).

After the experiment, their average percentages rose to 83.33, 73.33, 77.10, and 78.03, respectively. The dependent samples t-test analysis indicated that their post-test scores were significantly higher than the pre-test at a 95 % confidence level. In addition, their normalized learning gains or <g> values fell in the medium range for energy and reaction progress (0.63), factors influencing rate (0.66), and total (0.67), and fell in the high range for the definition of reaction rate (0.71), see Figure 5. It can be seen that the students obtained a higher score percentage and normalized gain for the concept of the reaction rate than for the concepts of energy and reaction progress and factors influencing rate. This arose from the idea that the definition of reaction rate involves less complexity. In contrast, factors affecting the rate involve various elements (concentration, surface area, temperature, etc.), and each factor uniquely impacts the rate (Çalik et al., 2010).

Figure 5:

Percentages of pre- and post-conceptual test scores (left scale) and normalized gain or <g> (right scale) of chemical reaction rate.

This showed that implementing a portable syringe kit demonstration of a gas-generating reaction effectively encouraged students to understand the reaction rate accurately. This is consistent with earlier research studies, which showed that using the corresponding chemistry experiment through an inquiry-based learning process assisted students in improving their conceptual understanding of chemical reaction rate (Çalik et al., 2010; Chairam et al., 2009; Supasorn et al., 2022).