Unit 2: Applying Problem Based Learning to the Science Classroom using the Scientific Method

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Unit Objective

After completing this unit the learner will be able to:

  • Modify and restructure a given investigative activity into a problem based learning task.

Scientific Method A Useful Process

When students participate in a PBL task, they utilize processes that allow them to demonstrate the mental and physical behaviors of scientists. In the process, they learn more than simple science concepts and skills. They learn a practical, useful real-world approach to solving problems and answering questions. The inquiry process involves the following steps.

  1. Observe a process or event
  2. Formulate questions based on observations
  3. Develop a workable hypothesis
  4. Devise a strategy for testing it
  5. Analyze and draw conclusions from collected data
  6. Review and evaluate conclusions
  7. Communicate findings to others

As you may notice these steps are uncannily similar to the general steps of the scientific method. The PBL or Inquiry-Based Learning allows teachers to break out of the direct instruction mode. Using PBL in the classroom does take time and patience, but eventually students will learn to make decisions and solve every day problems.

Examples of Scientific Method PBL Lessons

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Generating problem based learning tasks for the classroom can be quite a challenge. In the science classroom teachers rarely allow students to investigate outside the parameters of a typical activity. Problem based learning tasks can easily be created from a normal laboratory investigation by simply restructuring the activity. For instance there are several teacher designed laboratory investigations where students are given a limited set of materials and procedures to follow. The students are not aware of the end result, but the teacher has purposefully chosen these materials so students can master the concept with ease. Problem based learning alternatively allows students to select their materials from a wide variety of items, and requires them to construct and design their own investigative procedure.

All of the following tasks have numerous teacher designed laboratory investigations, but by asking students to develop and design their own investigative method we not only engage but challenge them to learn more than the discreet science concepts and skills.

The Cat's Meow

In this successful minds-on inquiry lesson elementary or secondary students can investigate numerous scientific concepts using milk, food dye, and liquid dish soap. According to Bergman and Olson (2011), the activity is ideally suited for teaching students important concepts in experimental design: features of a researchable question, how to design fair tests, controlling variables, multiple trials, data analysis, and supporting conclusions with evidence" (p. 45).

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Students perform this investigation and as the dish detergent is added students begin to examine the materials more closely. This lesson asks students to describe and explain the phenomenon they experience when the milk, dawn, and food dye begin to swirl creating a tie-dye effect. At any age this PBL could be performed. In the secondary setting I would recommend this for an introductory PBL in the school year.

As the teacher you will ask students to select a "testable" question they could actually investigate in the classroom with the available methods and materials. Probing them for details about their new investigation. How will they remember their observations and present the data to the class? How many times will the need to run their investigation? These type of questions related to the core of a successful investigation allow students to critically examine and reflect their ideas. "These experiences should help students move away from thinking that the goal was to learn about milk and its properties, but instead focus on their ability to do scientific inquiry" (Bergman & Olson,p. 47).

The Effects of Acid Rain on Vegetation

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This lesson can be applied to any secondary Biology or Environmental Science classroom setting and provides a research based PBL. Using their prior knowledge students will construct a concept map to help organize their research and fill in any gaps in their prior knowledge. Time must be set aside for students to research guiding questions about acid rain. Armed with their knew researched knowledge students will create the procedures for their controlled experiment, run the experiment, analyze their data, and make conclusions about the effect of acid rain on vegetation growth.

Throughout the initial design of the experiment teachers can once again ask guiding questions to help students reflect and examine their experimental design.

Redesign An Activity into a PBL

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Using your journal once again reflect on the steps of the PBL process from Unit 1 and its goals. Read the following activity, how would you restructure the activity and introduce it as a problem based learning activity? As you read the activity remember that PBL tasks start with the end in mind. Begin to create a problem that students can work with in order to investigate the concept of the effects on the rate of a reaction. Ultimately think of the guiding question that will inspire students thinking. How will you guide students to investigate variables such as surface area, temperature, pressure, catalysts?

Plop, Plop, Fizz, Fizz - Rate of Reaction

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Alka-Seltzer® tablets fizz furiously when dropped into water. The moment the tablet starts dissolving, a chemical reaction occurs that releases carbon dioxide gas. You may have seen a television commercial for Alka-Seltzer tablets, or heard one of their advertising slogans: "Plop, plop, fizz, fizz, oh what a relief it is!®" When you drop the tablets in water, they make a lot of bubbles, like an extra-fizzy soda. And like a soda, the bubbles are carbon dioxide gas (CO2). However, with Alka-Seltzer®, the CO2 is produced by a chemical reaction that occurs when the tablets dissolve in water.

The main ingredients of Alka-Seltzer tablets are aspirin, citric acid, and sodium bicarbonate (NaHCO3). When sodium bicarbonate dissolves in water, it dissociates (splits apart) into sodium (Na+) and bicarbonate (HCO3−) ions. The bicarbonate reacts with hydrogen ions (H+) from the citric acid to form carbon dioxide and water. The reaction is described by the following chemical equation:

So how does temperature come into this? In order for the reaction shown above to occur, the bicarbonate ions have to come into contact with the hydrogen ions. Molecules in a solution are in constant motion, and are constantly colliding with one another. The hydrogen and bicarbonate ions must collide at the right angle and with enough energy for the reaction to occur. The temperature of a solution is a measure of the average motion (kinetic energy) of the molecules in the solution. The higher the temperature, the faster the molecules are moving. What effect do you think temperature will have on the speed of the bicarbonate reaction? You can find out for yourself by plopping Alka-Seltzer® tablets into water at different temperatures, and timing how long it takes for the chemical reaction to go to completion.

How does the form of the tablet (solid, chunks, powder) play a role in the speed at which it dissolves? What effect do you think particle size will have on the speed of the bicarbonate reaction? You can find out for yourself by changing the Alka-Seltzer® tablets size by breaking the tablets into equal quarters, crush the tablet, and lastly use the entire tablet. Again time how long it takes for the chemical reaction to go to completion.

To do this experiment you will need the following materials and equipment:

  • At least 12 Alka-Seltzer® tablets (if you plan to do additional variations to the project, you'll want to get a larger box)
  • Thermometer (good range would be -10°C to 110°C
  • Clear 12 ounce (355 mL) drinking glass (or larger)
  • Measuring cup
  • Masking tape
  • Something to stir with (a teaspoon or a chopstick, for example)
  • Hot and cold tap water
  • Ice
  • Stopwatch
  • Lab notebook
  • Pencil


Darling-Hammond, L. et al. (2008). Powerful Learning: What We Know About Teaching for Understanding. San Francisco, CA: Jossey-Bass.

Egbert, J. (2009). Supporting learning with technology: Essentials of classroom practice. Upper Saddle River, NJ: Pearson Education, Inc.


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