Developing and Implementing Inquiry-Based, Water Quality

Article pubs.acs.org/jchemeduc

Developing and Implementing Inquiry-Based, Water Quality Laboratory Experiments for High School Students To Explore Real Environmental Issues Using Analytical Chemistry Daphna Mandler,* Ron Blonder, Malka Yayon, Rachel Mamlok-Naaman, and Avi Hofstein Science Education Department, The Weizmann Institute of Science, Rehovot 76100, Israel S Supporting Information *

ABSTRACT: This paper describes the rationale and the implementation of five laboratory experiments; four of them, intended for high-school students, are inquiry-based activities that explore the quality of water. The context of water provides students with an opportunity to study the importance of analytical methods and how they influence our everyday lives. It also provides an opportunity to expose students to scientific methods (e.g., inquiry) and behavioral responsibility that could influence their future lives as citizens. The inquiry-based activities consist of two parts. In the preliminary experiment, an analytical technique was introduced and the students learned analytical skills. On the basis of these preliminary experiments, the students designed inquiry-based laboratory experiments involving relevant questions and decision making. Students explored parameters concerning water quality from different sources and had an opportunity to evaluate the data critically and to answer questions such as the following: Should we drink bottled water or tap water? How is the water quality monitored? What does water contain? The experiments involve qualitative and quantitative analyses of water salinity, water hardness, and the presence of organic compounds (volumetric versus spectrophotometric analysis of chloride in water), as well as determining water hardness by EDTA complexometric titration and water filtration. KEYWORDS: High School/Introductory Chemistry, Analytical Chemistry, Environmental Chemistry, Laboratory Instruction, Inquiry-Based/Discovery Learning, Interdisciplinary/Multidisciplinary, Student-Centered Learning, Curriculum, Water/Water Chemistry

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RATIONALE The five experiments investigated drinking water quality using these simple qualitative analyses: conductivity, pH, qualitative tests of salinity (Cl−), and hardness (Ca2+ and Mg 2+). The four activities included several quantitative analytical methods via the IBL approach (Table 1): Complexometric titration for determining water hardness Fajans volumetric titration for determining water salinity Spectroscopy analysis for determining salinity and comparing it to the volumetric method Adsorption method in the adsorption platform activity The sequence of the laboratory activities was constructed to develop the students’ sense of the “need to know”10 which parameters influence and determine water quality in order to encourage them to explore these parameters. The leading questions: “What water is considered safe to drink?” and “How do we judge water quality?” guided students throughout the learning process and the analytical experiments and provided them with the tool to answer these questions. The activities were designed to involve the students in a “need to take an action” format. Namely, following the learning process, the students assess and evaluate the data provided by the municipalities and water companies. The students compare the results they obtain regarding water hardness, for example, with data published by the municipality responsible for supplying the water sample. The students also compare the

ater is the most abundant substance on Earth’s surface; it is a familiar substance in our everyday lives. The unique chemical properties of water make it an ideal medium for exploring analytical chemistry. Because of the solubility proprieties of water, many substances, mostly minerals, readily dissolve in water. Interactions with natural and artificial systems lead to a diversity of aqueous solutions that play key roles in environmental phenomena. Because of the lack of potable water around the world, both in terms of quality and quantity, analytical methods are needed to properly evaluate and treat water. Water purification requires adherence to a series of quality criteria embodied in physical, chemical, and microbiological parameters, all of which require analytical methods for measurement. Many activities and educational projects have involved evaluating quality water, for example, Globe, the Global Experiment for the International Year of Chemistry,1 and several others.2,3 Thus, the context of water provides teachers with an opportunity to expose high school students to analytical methods4 and to stimulate civic responsibility that could influence their future lives as responsible citizens.5,6 This article discusses the implementation of an inquiry-based laboratory (IBL) approach in an analytical chemistry laboratory for highschool students, where water analysis was the subject explored. The activities associated with inquiry-based laboratories7−9 include identifying questions, designing and conducting scientific investigations, formulating and revising scientific explanations, recognizing and analyzing alternative explanations, and communicating and defending scientific arguments. In the current paper, we present the way in which we integrated these stages of IBL into four analytical experiments. © 2014 American Chemical Society and Division of Chemical Education, Inc.

Published: February 12, 2014 492

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Table 1. Brief Description of the Laboratory Activities Activity 1. Taste and test bar 2. The hardness of water is measured using complexometric titration13 3. Fajans volumetric method for determination of chloride ions14 4. Spectrophotometric determination of chloride ions15 5. Adsorption platform

Laboratory Activities Students are asked to taste three samples of water and decide which tastes the best. Preliminary tests of drinking water from different sources include conductivity, pH, qualitative tests of salinity (Cl−), and hardness (of Ca2+ and Mg2+). Determination of water hardness from different water sources. Students are asked to bring to the lab water samples from different sources, for example, from different mineral water companies or water from different areas in Israel.

Determination of chloride concentrations from different water sources. Low concentrations cannot be detected by the Fajans method. High-concentration solutions must be diluted when using the spectrophotometric method. During the experiment the students use different adsorption platforms that are used to purify drinking water at home. The students evaluate the adsorption of different platforms by comparing salinity, hardness and organic compounds in a treated water sample.

these ions in water?” “Which methods are used to analyze water?” To answer these questions, students learn in class about the content of water, national or world regulations, the process that tap water undergoes from water sources in nature until it reaches the tap, and about analytical chemistry methods used to determine water content, and so on. These topics are learned as the students perform the IBL activities. Table 3 presents a list of the experiments performed and some of the inquiry questions that students raised in the different IBL activities. The three first IBL activities that the students perform, following the learning process in class, are well-known analytical methods that have been described previously in the literature.18−20 The three activities include these: (i) water hardness determination by complexometric titration; (ii) Fajans volumetric determination of chloride ions; and (iii) spectrophotometric determination of chloride ions. The fourth experiment deals with water filtration and adsorption platforms and is based on a novel procedure that was developed for the current program. The detailed manual can be found in the Supporting Information.

data with national standards. As a result of what they learned, they can now express a science-based opinion and take appropriate action if the data do not meet the specified national and local standards. This process is in line with the approach that students should learn about the role of chemistry in modern society and that students should play a key role as responsible, well-educated citizens;10 it has been the focus of two EU projects in recent years.11,12

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DESIGN OF THE INQUIRY EXPERIMENTS The laboratory experiments serve as key tools that underscore the theoretical concepts in real-life scenarios. All activities except the first, Taste and Test Bar, are designed as inquirybased laboratory activities.8,16 In the IBL experiments, each group of students raises their own inquiry question and designs their own inquiry experiment to investigate their inquiry question. Table 2 provides an example of the phases of the IBL activities in an experiment; the other IBL activities are elaborated on below. Taste and Test Bar Experiment

The goal of this experiment is to create the “need to know” notion, which will motivate students to engage in the subsequent IBL activities. In this preliminary activity, the students test drinking water from different sources. The first test is a taste test in which students are asked to choose the tastiest water from three unknown samples: mineral water, tap water, and filtered water. All taste tests are done outside the laboratory classroom to avoid drinking inside the laboratory. Students fill-in their preferred water in a Google form17 (see also the Supporting Information) that compiles the results online automatically; therefore, the class statistics are immediately shown. (This test showed that none of the water samples was “the tastiest” for all the students. As taste always is a subjective property, it gives the opportunity to discuss in lab with the students the notion that taste is not a method to characterize water quality and the students by themselves raised the need to find objective tests to distinguish between the water samples.) In the second part of the first laboratory activity, the students become acquainted with parameters that influence water quality such as acidity, conductivity, and water hardness, as well as water salinity. They use simple qualitative methods that later can be used to explore some of these factors quantitatively. This qualitative activity raises some relevant questions, such as “How can quality indicators of water be measured quantitatively?” To answer this question, students need to ask and consider other questions such as: “Is there a parameter for minimum and maximum consumption of chloride ions and calcium ions?” “What influences the concentration of these ions in water?” “Why is it important to analyze the concentration of

Water Hardness Determination by Complexometric Titration

Water hardness is usually determined by titration with a standard solution of ethylenediamminetetraacetic acid, EDTA. The EDTA is a complexing or chelating agent used to capture the metal ions. At the preinquiry phase, students gain experience with the titration method and determine the end point of the titration as well as the calculation involved. At the inquiry phase they ask questions such as “How does the water’s origin influence its hardness?” They design and conduct experiments in order to evaluate the dependence between the water’s origin and its hardness. Fajans Volumetric Determination of Chloride Ions

This experiment involves the reaction between silver ions and chloride; it is used to illustrate volumetric precipitation analysis in which the reaction product is an insoluble substance. The endpoint detection is based on the formation of a colored adsorbed layer on the silver chloride precipitate. A sample question the students can ask is “How does the temperature influence the chloride ion concentration?” Students design experiments using water having the same origin at different temperatures. After conducting the experiments, they can evaluate whether temperature has any influence on water salinity. Spectrophotometric Determination of Chloride Ions

The spectrophotometric method can be used for direct determination of the chloride ion content in precipitation samples ranging from 0.05 to 5 mg/L. Chloride ions will substitute for the thiocyanate ions in undissociated mercury 493

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Analyzing the results, asking further questions, and presenting the results scientifically

thiocyanate. The released thiocyanate ions react with ferric ions, forming a dark red iron−thiocyanate complex. The absorbance is measured at 460 nm. The students can investigate how different purification methods influence the chloride ion concentration. Next, they can evaluate the difference between the volumetric and the spectrophotometric methods. These methods are used to analyze chloride and calcium ion concentrations in mineral water with high and low chloride concentrations as well as in tap water from different sources. In discussing each of these experiments, a statistical analysis of the data from the class is prepared regarding the reliability and accuracy of the results when comparing the average results of the class with the percentage of components stated on the label of the bottle or supplied by the municipalities. Water Filtration and Adsorption Platforms

The IBL scenario was implemented according to Kipnis and Hofstein, ref 16.

The last activity deals with water filters and involves questions such as “Which filter should we buy for our home?” In this experiment, the students use different adsorption platforms in order to evaluate their water purification characteristics. Different adsorption platforms have different adsorption capacities. In the laboratory the students reproduce the purification process that water undergoes in nature and the purification process it undergoes at home when the tap is turned on. They evaluate sand, activated carbon, the cations’ adsorption platform, and the water softener platform, which is a combination of anion and cation exchangers. Through this experiment, the students practice analytical skills, such as preparing a column and evaluating the quality of different adsorption platforms and qualitative precipitation reactions. (Instructions for performing the “Adsorbent Platform” experiment are available in the Supporting Information; a description of the hazards associated with the experiments is also available in the Supporting Information.) An example of the different phases of the IBL activities is shown in Table 2. Each experiment introduces another idea in analytical chemistry, beginning with a relatively easy procedure such as volumetric titration. Titration is a familiar method that introduces the notion of a method’s limit; this is followed by determining water hardness by complexometric titration, which involves more difficult concepts, procedures, and calculations, such as calcium ion concentrations and the units used to represent hardness. The next analytical method is spectrophotometric determination of chloride ions, which is based on difficult concepts of spectroscopy, Beer−Lambert’s law, and dilution of solutions. Finally, the methods of purification used in the adsorption platform activity are analyzed by students using the previous methods to evaluate the water sample after filtering in different platforms. The students can analyze the influence of molecular interaction on the efficiency of each adsorption platform.

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EVALUATION OF THE IBL EXPERIMENTS A study was undertaken to assess students’ attitudes toward the analytical content in an environmental context. The study consisted of 400 high school students in the 12th grade from 18 schools in Israel. These students were taught the water unit by their chemistry teachers, who had previously participated (2007−2009) in a workshop that trained them how to teach the unit. A thorough study was conducted to evaluate the water activities, in partial fulfillment of the first author’s Ph.D. dissertation, which was published elsewhere.21 A sample follows of students’ responses that were recorded during interviews.

a

Titration of different water samples from different mineral water brands.

Planning an experiment

Asking questions, phrasing an inquiry question, and hypothesizing The Inquiry Phase of the Experiment How does the origin of mineral water influence water hardness? Mineral water from the Golan Heights contains less Ca2+ compared to water from a fountain near the Dead Sea since the soil is mainly limestone. The soil in the Golan Heights is mainly basalt.

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1. Ask relevant questions. Choose one question for further investigation (Table 3) and rephrase it as an inquiry question. Formulate a hypothesis that is aligned with your chosen question. 2. Plan an experiment to investigate the question under consideration. Ask the teacher to provide you with the equipment and materials needed to conduct the experiment. 3. Conduct the experiment that you proposed. Observe and clearly note your observations. Discuss with your group whether your hypothesis was correct or you had to reject it.

Describe in detail the apparatus in front of you. Observe and record all important details in your notebook while performing the preliminary experiment.

Observing and recording, performing titrations, determining end points, and calculating water hardness

Students’ Activities

Preinquiry Phase Titration of a known concentration of Ca2+ ions with EDTA solution in order to determine water hardness for a standard solution.

Student Instructions

Table 2. An IBL Example Scenario Determining Water Hardness by a Complexometric Titration Experimenta

Abilities and Skills

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Table 3. Sample of Inquiry Questions That Students Explore in the Different Analytic Methods The Experiment

Examples of Inquiry Questions Raised by the Students

Water hardness determined by complexometric titration Volumetric determination of chloride ions Spectrophotometric determination of chloride ions Adsorption platforms

How do filtration methods influence water hardness? How does the water’s origin (the type of mineral water, in my house, in my country) influence the water hardness? How does the water chloride ion concentration change during a rainy season? How does the number of filtrations influence the water chloride ion concentration? How does temperature influence the water chloride ion concentration? How do seasons of the year (rainy season compared to the dry seasons) influence the chloride ion concentration? How does the amount of water softener influence the amount of chloride ions in the water sample? How does temperature influence the activated carbon adsorption of organic matter in the water sample?

river near their school; they were so enthusiastic that they investigated more than what they were required to do in school and they won an award for excellence in a national contest of inquiry-based experiments, which took place in April 2010.

The students mentioned the importance of learning the environmental analytical unit. One of them offered this opinion: Chemistry in an environmental context is more important for everyday lives than are acids and bases. I don’t always see its connection to everyday lives. I know it exists there, but I cannot always make the connection. Most of the students reported that they appreciated the unit more than their regular chemistry course. Students said that they especially appreciated the feeling that they could discover things by themselves, “[W]ith all the concentration measurements in the laboratory, now I know it should concern me. It makes it more interesting.” In addition, some students reported that they now better understand why they have to perform laboratory activities. They referred to a sense of purpose “We were doing real experiments, with a purpose.” As the following quotations show, students felt that the unit helped reduce the incongruence between concepts in the chemistry lessons and increased the concepts’ relevance to their everyday lives and to the learning process. The students expressed it while comparing their regular textbook with the unit: You know all the time why you do things, like the experiments. Yes, like the laboratory work, we are doing now [referring to some recent experiments in the regular chemistry lesson], I don’t know what we are doing. Ok, I do it, but why? What does it mean? I enjoyed it more than using the book, because now we know what we are doing while performing those experiments why we were doing them, what we were actually doing, and why. Another student commented: These activities are related to other concepts we have learned such as ions and solubility. This is very important since it helps me understand what ions do in water and how they influence the water quality and also what norms define water quality. The students found the sequence of activities to be coherent and meaningful: The laboratories, on the one hand, require a high standard of performing complex skills, knowledge of laboratory instruments, order, and organization. But this has an advantage in raising the level of thinking. I expect to have difficulties, but it's good to deal with an interesting flow of activities. I loved the laboratory about various filters; it is a very relevant topic. The students expressed their appreciation of the logic of the flow of activities as well as the content. The question “What and how much dissolves in water?” arose and then the students explored the differences in the parameters they had learned with different water sources. The students found it interesting to compare the water from their neighborhood to the water from other parts of the country. They analyzed the water in a

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DISCUSSION In the course of the laboratory activities, the students analyze water, which they use in their everyday lives. They feel a sense of importance when they get accurate results and are surprised to see the variability of chloride concentrations in samples from different sources; this raises new questions related to these sources (tap water from different sources, mineral water manufactured by different firms, seasonal water pools, etc.). Students are disappointed or sometimes surprised when the chloride concentration that is stated on a bottle is low and nothing precipitates even after it is titrated with a large volume of AgNO3. Through these experiences they learn that a certain analytical method may not be suitable for detecting low concentrations of a material, which brings about the need to choose a more appropriate means, such as the spectrophotometric method. The idea that each method has its limitations is dealt with theoretically and in practice. While following the sequence of activities, students have an opportunity to discuss which method is preferable for the purpose that was stated on the label of a bottle, for example. The analytical IBL experiments discussed here provide the students with an opportunity to construct their knowledge by actually doing scientific work. In other words, students are provided with a learning situation in which they control their own learning in striving to understand the scientific principles underlying the experiment.21 Students design and perform their experiment and evaluate their results. More specifically, they focus on the accuracy, precision, reproducibility, and standard deviation, while evaluating the results. The students also experience real-life environmental problems and develop environmental sensitivity. Their understanding of the importance of preserving the environment may influence their adult lives. At the end of each IBL activity, the whole class discusses the results and conclusions. The students gather the different investigation results and draw more comprehensive conclusions regarding the water that was tested. Finally, they integrate an analytical laboratory with an environmental context, which gives students a unique opportunity to use laboratory results in a real-world context. Using environmental-effects monitoring and performancebased analytical methods provides students with a common terminology with which to interpret and assess chemical data. The activities illustrate how conceptual understanding and investigative skills work. Moreover, they promote the critical thinking and decision making needed to answer the leading questions and provide high school students with experience in conducting an authentic scientific investigation. 495

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(18) Harris, D. C. Quantitative Chemical Analysis; Macmillan: New York, 2010. (19) Wentworth, R.; Wentworth, R. S. Experiments in General Chemistry; Houghton Mifflin Co,: Boston, MA, 1987. (20) Greco, T. G.; Rickard, L. H.; Weiss, G. S. Experiments in General Chemistry: Principles and Modern Applications, 8th ed.; Prentice Hall: Upper Saddle River, NJ, 2002. (21) Mandler, D.; Mamlok-Naaman, R.; Blonder, R.; Yayon, M.; Hofstein, A. High school chemistry teaching through environmentally oriented curricula. Chem. Educ. Res. Pract. 2012, 13, 80−92.

ASSOCIATED CONTENT

S Supporting Information *

Form for “Taste and test drinking water”; instructions for performing the “Adsorbent Platform” experiment; hazards associated with the experiments. This material is available via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Davidson Institute of Science Education at the Weizmann Institute of Science for their continuing support. REFERENCES

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