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Transition from cookbook to problem-based learning in a high school chemistry gas law investigation.

INTRODUCTION

The Australian senior science curriculum includes an in-depth study of gases and the gas laws. Science activities such as investigations test student ideas, predictions, and hypotheses from which they can draw conclusions in response to questions or problems (ACARA, 2015a). Problem-based learning (PBL) integrates authentic learning situations or problems into daily classroom activities, moving beyond traditional forms of instruction that are unresponsive to students' thinking, lack disciplinary rigour, and are often the norm in science classrooms (Windschitl, Thompson, & Braaten, 2011). PBL is one means of improving student engagement with scientific content. However, as a chemistry teacher of twenty-five years, I have found that the laboratory investigations associated with the study of gases have not changed significantly. Currently, I feel that there is a need for updated high school chemistry practicals that reflect the recent paradigm shifts in education, moving away from traditional cookbook practicals to authentic problems that promote student thinking and problem-solving skills.

With the introduction of recent changes to the school curriculum, high school chemistry courses were redesigned, emphasising learning experiences that connect with students' interests and experiences. Students should therefore have multiple opportunities to explore key concepts and models through active inquiry as they design and conduct investigations through questions, hypotheses, manipulation of variables, analysis of data, evaluation of results, solving problems and developing and communicating evidence-based arguments (ACARA, 201 5b). Current science curricula have tasked teachers with aligning classroom activities with the philosophy of PBL. In this article, I will describe a chemistry gas experiment that I developed with the intent of integrating inquiry and PBL. The lab activity follows the principles of Ambitious Science Teaching (AST). Teachers (1) engage students with important science ideas, (2) elicit students' ideas while making visible what students currently know about the science being taught, (3) guide sense-making talk around investigations and lab activities to support changes in thinking, and (4) develop evidence-based explanations by scaffolding students' efforts to put everything together (Windschitl, Thompson, Braaten, & Stroupe, 2012). Additionally, the lesson plans incorporate a 'Driving Question', a themed question written on the board (SMART, white or blackboard) that supports inquiry and PBL by organising and focusing students' questions and linking them to the learning objectives of the activity (Weizman, Shwartz, & Fortus, 2008).

THE INVESTIGATION

Instructional goals

Students will be able to:

1. develop and apply the Ideal Gas Law, and Dalton's law of partial pressure;

2. show mastery of mathematical operations connected with the conversion of units of measure;

3. use modelling, observation, analysis, and the experimental and empirical methods of laboratory work;

4. use reliability, accuracy and sensitivity of measuring instruments to interpret measurement results (significant figures, uncertainty related to measurements, errors).

Context

* Year level: senior secondary chemistry curriculum (Year/Grade 11/12).

* Duration of activity: Total lab time 50 minutes; plus 30-50 minutes of teacher-guided discussion and group discussion following the lab activity.

* Class size: my class size ranges from 20-34 students. Small classes include special needs students. Students work in heterogeneous groups of three, which change every two months. Working in heterogeneous groups ensures that all students can perform practicals, with help from their group.

* Safety precautions: All students wear safety goggles during lab investigations. Students are shown how to extract the syringe plunger when the syringe is empty. This requires two students as the vacuum created when the plunger is pulled to the point when the nail is inserted is difficult.

THE TEACHER LESSON PLAN

(Guided questions and teacher prompts following the principles of AST.)

This lesson plan includes the following steps.

* Step 1 (5 mins): Introducing the concept

In this step, the teacher introduces the Driving Question of this lesson: "If we exhale carbon dioxide and inhale oxygen, why is mouth-to-mouth resuscitation effective for a person who is not breathing?"

* Step 2 (5-10 mins): Background Knowledge Probes (BKPs)

I ask a series of questions based on data from previous lab investigations and from class discussions to have students develop the mathematical expression of the Ideal Gas Law. In their lab groups, students are asked to combine all variables from previously studied gas laws into one equation, PV = nRT. I ask a series of probing questions: "What are the percentages of the gases found in air? Can you develop a procedure to measure the molar mass of air? How could you determine the number of moles of the constituent gases in air? If you know the pressure of air, how could you determine the pressure of each individual gas in air?"

* Step 3 (45-50 mins): Collecting and Making Sense of Data

Students collect their data and work through a series of mathematical manipulations to determine the molar mass of air and exhaled air, the moles and density of each gas in air and exhaled air.

* Step 4 (25-50) mins: Developing Evidence-Based Explanations

I engage students by inviting them to share the data that they gathered from the activities with other groups and with the class, and together we summarise data on the board.

* Step 5: Evaluation

Students are asked to hand in lab reports for evaluation. There is a formal assessment or unit test that covers the concepts presented in the unit on gas, including the behaviour of gases in the world around us and some of their related applications.

INSTRUCTIONAL MATERIALS

Materials
Electronic balance  Sealed 140 mL
measuring 0.01 g    syringe, modified
                    with a nail*
Barometer or        Thermometer
Internet search
for atmospheric
pressure
Balloon


*The modified syringe is a crucial part of this investigation. The lab does not use a balloon or baggie to measure the mass of a gas, which is important as many gases are less dense than air, and are therefore buoyant. This means that measuring their mass directly on a balance is not feasible. Our school lab technician drilled a hole through 12 syringes close to the 140 ml_ line. A nail rests in the hole. The purpose of the nail is to provide a constant volume of gas in the syringe. The syringe has a removable stopper.

Student Handout

A Summary of the Activity

I show students the empty syringe, with the piston lowered. I ask the class: "Is the syringe empty?" (it is not, since there is air above and around the piston). Then, I ask the students: "What can you do to ensure that there is no air in the syringe?" Students manipulate the syringe and nail as they solve the problem of how to mass a syringe that is devoid of air. What needs to happen is that students pull the plunger of the "empty" sealed syringe and fit the nail in the drilled hole. This is difficult because a vacuum is created, requiring two students working together: one student pulls the plunger, and a second student inserts the nail. I also ask the students: "How could you determine the mass of air? How could you determine the mass of exhaled air?"

The temperature and the room pressure are measured using a thermometer and barometer (or teachers can go to http://www.theweathernetwork.com prior to the beginning of the lab).

Procedure

(The teacher should guide students to develop the procedure. In a PBL activity, students should develop their own working procedure. The procedure provided below is for the teacher.)

1. Place the stopper on the plastic syringe and pull out the plunger of the syringe to create a vacuum.

2. Put the nail through the hole to ensure that the plunger remains in place and weigh the mass of the syringe using the scale. Record results.

3. Remove the stopper from the syringe allowing atmospheric air to enter, and weigh the mass of the syringe plus air using the digital balance.

4. Calculate the mass of air by subtracting the mass of the syringe containing air from the mass of the vacuum syringe. Record results.

5. Let the air escape. Seal the syringe, and pull out the plunger to create a vacuum.

6. Put the nail through the hole to ensure that the plunger stays in place. Blow air into a balloon, and place the balloon over the syringe and stopper.

7. With the balloon over the syringe, carefully remove the stopper. The students must hold the stopper while it is inside the balloon, using the skin of the balloon.

8. Allow the exhaled air to enter the syringe.

9. With the balloon still over the syringe, replace the stopper and then release/remove the balloon.

10. Weigh the mass of the syringe containing the exhaled air and calculate the mass of exhaled air by subtracting the mass of the syringe containing the exhaled air from the mass of the vacuum syringe. Record results.

Students determine:

* Molar mass of air and exhaled air using the Ideal Gas Law

* Moles of gas in air and exhaled air

* Partial pressure of individual gases in air and exhaled air by multiplying the atmospheric pressure in the classroom by the % abundance of each gas found in air, or in exhaled air. Students find the % abundance on the Internet.

* Moles of each component of individual gas in air and exhaled air

* Density of each individual gas in air and exhaled air

Prior to experimentation, I spend 15-25 minutes probing and questioning students with the intent of drawing out prior understanding of the Ideal Gas Law, with the goal of having the students determine how to measure the molar mass of an unknown gas on their own, with the guidance of directed teacher questioning. Students are shown the equipment, and are given time to develop their procedures. I discuss the procedures with each group before they begin the investigation. Following the investigation, students complete all calculations which are due the following class. During the following science lesson, students are given time to work in their groups, to verify the calculations, uncertainty, and significant digits with their group members. I circulate around the room, spending time with each group while probing for understanding of the gas laws, and checking the correctness of their calculations. I collect the final practical write-up two classes following the investigation.

CONCLUSIONS

Incorporating inquiry and PBL into my high school chemistry classes has had a positive effect on student engagement. We have noted that the number of students dropping chemistry for other non-science options has diminished. One notable and unexpected result of using a Driving Question to anchor lessons is that students began to use the Driving Question in their lab report conclusions. When asked, my students found the use of PBL in chemistry labs "effective and enriching, especially considering that they relate to current problems which prepare students for college", and they "prefer a more contemporary teaching method... rather than traditional" (student quotes, 2016-2017). This is consistent with the literature, where it has been found that students enjoy PBL instruction more when compared to traditional instruction (Goodnough & Cashion, 2006).

This lab provides students with an opportunity to answer a question about CPR, to use scientific inquiry, to plan, investigate, gather data, think critically and logically about relationships between evidence and explanations, construct and analyse alternative explanations, and communicate scientific arguments in a formal lab report. Scientific literacy develops as students actively engage with problem-solving, inquiry, and critical thinking while integrating science, technology, engineering and math (STEM) (Asghar, Ellington, Rice, Johnson, & Prime, 2012). Teachers are encouraged to incorporate inquiry and PBL activities. The emphasis on using real-world problems to anchor chemistry content required a paradigm shift for me, and for many in-service science teachers. I developed this lab to provide an opportunity to incorporate inquiry and PBL into my high school chemistry course.

REFERENCES

ACARA. (2015a). Australian Curriculum: Chemistry. Retrieved August 25, 201 7 from https://www.australiancurriculum.edu.au/senior-secondary-curriculum/science/chemistry/?unit=Unit%2B4

ACARA. (2015b). Australian Curriculum: Science. Version 8.0. Retrieved August 25, 2017 from https://www.australiancurriculum.edu.au/download?view=ss

Asghar, A., Ellington, R., Rice, E., Johnson, F., & Prime, G. M. (2012). Supporting STEM education in secondary science contexts. Interdisciplinary Journal of Problem-Based Learning, 6(2), 84-125. doi:10.7771/1541-5015.1349

Goodnough, K., & Cashion, M. (2006). Exploring problem-based learning in the context of high school science - design and implementation issues. School Science And Mathematics, 106(7), 280-295.

Weizman, A., Shwartz, Y., & Fortus, D. (2008). The Driving Question Board: A visual organizer for project-based science. The Science Teacher, 75(8), 33-37.

Windschitl, M., Thompson, J., & Braaten, M. (2011). Ambitious pedagogy by novice teachers: Who benefits from tool-supported collaborative inquiry into practice and why? Teachers College Record, 113(7), 1311-1360.

Windschitl, M., Thompson, J., Braaten, M., & Stroupe, D. (2012). Proposing a core set of instructional practices and tools for teachers of science. Science Education, 96(5), 878-903. DOI:10.1002/sce.21027

Heather McPherson is a full time science teacher in Montreal, Canada, and is a PhD candidate in the Department of Integrated Studies in Education, Faculty of Education, McGill.

The situation

A group of teenagers is taking a first responder first aid course. The teacher is explaining how to perform cardiopulmonary resuscitation (CPR). One of the students asks: "If we exhale carbon dioxide and inhale oxygen, why would mouth-to-mouth resuscitation be effective for a person who is not breathing?"

Assignment

You must experimentally determine the difference between air and exhaled air in terms of moles of constituent gases, and density. Using your data, you must explain to the first aid students why mouth-to-mouth resuscitation is effective for a person who is not breathing.
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Author:McPherson, Heather
Publication:Teaching Science
Article Type:Report
Geographic Code:8AUST
Date:Mar 1, 2018
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