A Simple Oxygen Detector Using Zinc−Air Battery

Communication pubs.acs.org/jchemeduc A Simple Oxygen Detector Using Zinc−Air Battery Yoong Kin Hooi, Masayoshi Nakano, and Nobuyoshi Koga* Department of Science Education, Graduate School of Education, Hiroshima University, 1-1-1 Kagamiyama, Higashi-Hiroshima 739-8524, Japan S Supporting Information * ABSTRACT: The construction of a simple oxygen detector using a zinc−air battery as an oxygen sensor is described. It is a user-friendly device that can be employed in various laboratory activities in both junior and senior high schools. A short circuit can be introduced to reduce the O2 concentration in the air-diffuser layer of the battery that causes a decrease in the voltage. This phenomenon provides the basis to make an electrical device that can produce a voltage increase whenever oxygen gas is present. If the surroundings do not contain any available oxygen gas, the voltage in the zinc−air battery would remain static. In addition, time-to-operate of an electric component attached to the battery can also be used for semiquantitative determination of O2 concentration in a gas sample. KEYWORDS: Elementary/Middle School Science, High School/Introductory Chemistry, Demonstrations, Hands-On Learning/Manipulatives, Gases, Laboratory Equipment/Apparatus he detection and identification of O2 are common laboratory activities, which are introduced to students as early as elementary school. A flame test, in the form of relighting of glowing splinter, acts as a common and basic qualitative test for students to confirm the presence of O2. At a high-school level, a solution containing indigo carmine can be used to indicate the presence of O2. A semiquantitative measurement of O2 concentration can be performed using a gas detector tube.1 The measurement of O2 concentration using an electric sensor with a data logger is currently being introduced in school laboratories. This paper describes a new and simple method to qualitatively detect the presence of O2 and semiquantitatively measure the concentration. Commercially available zinc−air batteries have been used in various experiments in high schools.2−4 The zinc−air battery works in such a way that oxygen gas becomes the active cathode, while zinc is the anode contained within the battery. The respective electrode reactions of the zinc−air battery and the corresponding standard potentials of the equations as written are5 T ( −)Zn(s) + 2OH−(aq) → ZnO(s) + H 2O(l) + 2e− (E° = 1.25 V) ( +)O2 (g) + 2H 2O(l) + 4e → 4OH (aq) (E° = 0.4 V) (2) − − According to eq 3, the battery consumes atmospheric O2 and gains mass in the form of ZnO. Therefore, Faraday’s law can be confirmed by measuring the change in the volume of O2 consumed or the gained mass of the zinc−air battery with increasing quantity of electricity in a circuit using the zinc−air battery as the power source.2−4 At the operating voltage of the zinc−air battery (1.4 V), the electric current in a circuit, with a small resistance, linearly changes with respect to the atmospheric O2 concentration.5 This makes it possible to use the zinc − air battery as a sensor for measuring O 2 concentration. This idea is further developed by applying an equivalent circuit in a device.6 In this communication, we report a method to use a zinc−air battery in a very simple circuit for detecting O2 and semiquantitatively determining the concentration. With a very small residual O2 concentration in the air-diffuser layer of the zinc−air battery, the electromotive force of eq 3 dramatically decreases.7 The re-establishment of the electromotive force by exposure to O2 from a gas sample provides evidence for the presence of O2, and the recovery time is an approximate measure of the O2 concentration in the sample. The basic principle is described in the Supporting Information. (1) ■ The overall reaction of the battery is 2Zn(s) + O2 (g) → 2ZnO(s) (E° = 1.65 V) (3) A DETECTOR SETUP A simple handmade detector was constructed using a zinc−air battery (1.4 V Panasonic PR44 or 1.4 V Panasonic PR2330), rubber stoppers (size 2, 3, and 8), a glass tube, wires, a switch, and an electronic melody box P70−3934 (Narika, Japan). © XXXX American Chemical Society and Division of Chemical Education, Inc. dx.doi.org/10.1021/ed400169z | J. Chem. Educ. XXXX, XXX, XXX−XXX Relationship between duration time of the short-circuit treatment and the voltage recorded immediately after completing the short-circuit treatment (initial voltage) for the PR44 zinc−air battery. to investigate the voltage change (Figure 4). and a 15 s short−circuit time resulted in an air chargingtime of less than 30 min. The audio results can be explained by the voltage changes at each electrode shown in Figure 4 and the line showing the minimum voltage requirement of the melody box. By connecting the battery to a voltmeter. When a PR2330 battery was tested. (Bottom) A completed detector and (top) the corresponding circuit diagram.1021/ed400169z | J. XXX−XXX . the negative and the positive terminals were connected to cause a voltage drop. Then the zinc−air battery was fitted to a shaped rubber stopper. the melody box at anode produced sound after 2 min. Two detectors. Short Circuit and Detector Performance When a new zinc−air battery is first exposed to the atmospheric air.4 V. The time-to-sound values at the respective O2 concentrations are reproducible. an electronic melody box. Communication Figure 2. Voltage change at the anode and cathode in detectors during the electrolysis of water using the PR44 battery detector setup.2 V after a short-circuit time of 30 s (Figure 2). as can be seen in Figure 1. particularly after short circuit. The idea was to reduce the voltage to a value lower than the minimum requirement of the melody box. Leaving one hole open for gas sample intake. A calibration curve for the semiquantitative determination of O2 concentration using the PR44 battery detector setup. Figure 1. the voltage dropped to ca. The detector was constructed with a switch acting as an alternative circuit path for the short circuit.760 V. By implementing the idea of using a short circuit. SW is the switch and V is the voltmeter. When a PR44 battery was tested. A maximum voltage difference between the minimum requirement of the melody box and the voltage immediately after completing the short-circuit treatment of the battery gives optimum results for the qualitative and semiquantitative tests. XXXX. but no sound at cathode for more than 5 min. Chem. in this case. The relation between O2 concentration and time-to-sound can be empirically expressed by an inverse proportion. The relationship between the O2 concentration in the test gas and time-to-sound using the PR44 battery detector is shown in Figure 3. Educ.Journal of Chemical Education There are several air holes in these models of the zinc−air batteries. to provide ample time for the voltage hike to be detected by the electrical component. 0.org/10. dx.doi. This was done to reduce the rate of voltage increase by slowing the oxygen gas adsorption in the air-diffuser layer of the zinc−air battery. Electrolysis of Water box. ■ APPLICATION IN SCHOOL LABORATORIES Figure 3. the voltage immediately after the shortcircuit treatment (initial voltage) was investigated. XXX. 0. When two melody boxes were wired to the oxygen detector at each Figure 4. the voltage dropped to ca. similar to those shown in Figure 1. was 0. the voltage gradually rises and subsequently remains constant at around 1. other holes were sealed with a transparent tape. It is important.5 V with a short-circuit time of 30 s and resulted in an air-charging time of 30 min or more. were employed to verify the gas sample evolved from the electrolysis of water while being wired to a voltmeter instead of the melody B electrode instead of the voltmeters. in this case. which. This relation was used as a calibration curve to determine the O 2 concentration in a test gas. org/10. M. after the short-circuit treatment. (B)(22300272) and challenging exploratory research (23650511) from Japan Society for the Promotion of Science.) acknowledges the Ministry of Education.1 Human Breath Combustion of Candle a The initial voltage right after the short-circuit treatment is 0. This material is available via the Internet at http://pubs. if the initial voltage of the zinc−air battery.9 ± 0. Chem. 1763−1767. J. P.. ■ ■ ■ ■ (1) Collings. M. Chem. #3553.1021/ed400169z | J. Why Batteries Deliver a Fairly Constant Voltage until Dead. J.3 ± 0. (4) Kamata. (6) Takahashi. ACKNOWLEDGMENTS The present work was supported partially by a grant-in-aid for scientific research (A)(25242015). and more cost-effective than a gas detector tube. Kagaku to Kyoiku 2000. C dx.ac. Chem. Exploring Faraday’s Law of Electrolysis Using Zinc−Air Batteries with Current Regulative Diodes. J. 330−331. Application in Other Experiments The performance of the oxygen detector using the zinc−air battery in various experiments in student laboratory experiments is summarized in Table 1. Pure Appl.5 No sound (10 min) 1. Teaching Materials using Zinc−Air Batteries. Educ. T. (5) Tanaka. Yamauchi M. XXX. http://ma.1 8. II.3 11. Educ. ecsdl. Japan). C. 1416−1420.2 9.3 11. Hossain. 54 (9). (2) Kamata. AUTHOR INFORMATION Corresponding Author *E-mail: nkoga@hiroshima-u. (3) Kamata. As can be seen from these data (comparison of different gases). Educ. G.org. 13(1).1 12. In addition.8 8.ac. Science. 2007.13-10. Performance Standard for Detector Tube Units Used to Monitor Gases and Vapours in Working Areas. M.1 No sound No sound No sound 0. Educational Experiment for Faraday’s Law..8% O2)d After (15. Kawahara. ■ REFERENCES ASSOCIATED CONTENT S Supporting Information * Instructor information. XXXX.full.jp/v13n1/10_2d4_1. This can be observed in the results of the experiments for the human breath and the combustion of a candle. (7) Smith.9 No sound (5 min) 0.5 ± 0.2 V.2 ± 0. and Technology in Japan for the financial support in the Teacher Training Program.2 11.K.org/content/MA2012-02/51/3553. Paku. Educational Experiment for Faraday’s Law (2nd report). Abstract PRiME2012. N. Md. 192−194. cSee the Supporting Information. Notes The authors declare no competing financial interest.6 ± 0. Teaching Materials using Zinc−Air Batteries. Sports.. J.sci. A Convenient Measurement of Oxygen Concentration using Zinc−Air Battery. M.1% O2)d PR44a 1. Chem.4 PR2330b 2. No. 84 (4). easier to use than an indigo carmine solution.utsunomiya-u.4 ± 0.. 2009. CONCLUSION The simple device with a zinc−air battery as O2 sensor can be applied to various student experiments at schools. Koga. Culture. 674−676. the detector selectively works for oxygen.5 V. bThe initial voltage right after the short-circuit treatment is 0.Journal of Chemical Education Table 1.pdf (accessed Dec 2013). Educ.H. is set as constant in each experimental run.jp.2 9.8 ± 0. The detection and determination of O2 concentration is more quantitative than the conventional flame test.pdf (accessed Dec 2013).4 ± 0.0 No sound No sound No sound 1. I. http://chem.. Kagaku to Kyoiku 2000. Y. MacCarthy. M. Equivalent Circuits of Zinc−Air Battery and Analysis of Zinc−Air Battery Oxygen Sensor using the Equivalent Circuits.acs. Performance of the Oxygen Detector Using Zinc−Air Battery in Various Experiments Communication Time to Sound/min Experiment Water Electrolysis Comparison of Gases Gases O2 evolved from Anode (+) H2 evolved from Cathode (−) O2 by H2O2(aq) decomposition H2 by reaction of HCl(aq) + Zn(s) CO2 by reaction of HCl(aq) + Na2CO3(s) O2 consumed from air by chemical body warmer (kairo)c Oxygen inhaler (95% O2) Inspiration (18. A.9 ± 0. 48 (5).8% O2)d Expiration (16. Chem. 2012. 89 (11). The details of all the experiments listed in Table 1 are described in the instructor information found in the Supporting Information. 2001. 48 (3). 2012.9 ± 0. M. the concentration of oxygen can be semiquantitatively determined by comparing the time required by electronic melody box to make sound..doi.3 ± 0.2% O2)d Before (18. One of the authors (Y. XXX−XXX . dMeasured using an oxygen detector tube (Gastech.