Chemistry PBL
-
Level I
Essential Investigations
Teacher Guide - Essential Chemistry Investigations
Do not give Teacher Guide part of this handout to students. Give them Student Investigation Template, which is also included to this handout.
Investigation: Thickness of an Oil Film
Description
Students design and conduct their investigation to find the thickness of an oil spill as accurately and as precisely as possible. This activity is most effective if students have this learning experience after they have a basic foundation of drop calibration drops (with respect to mass and volume), density, and fundamental geometry.
Learning outcome
• Plan and implement a laboratory investigation.
• Apply concepts of density and process skills to determine the thickness of an oil spill. • Make measurements with accuracy and precision.
• Use significant digits in measurements and calculations.
Lab Management
1. Collect lab equipment and materials. Set equipment on each table for each lab group or instruct students to pick up materials from a central location. 2. Place small quantities of oleic acid in dropper bottles. Stretch the plastic
pipette ends to make fine micro-pipettes.
3. After completing investigation, ask students to clean and put away the equipment in the proper location. The large plant saucers may require thorough cleaning with dish soap and water to remove all traces of oil.
Safety
Students will review the laboratory safety precautions based on their plan. They will also review MSDS of the chemicals used in the investigation and identify hazards and safe handling/disposal of the chemicals.
All general lab safety precautions such as goggles and aprons are necessary. Oleic acid may be washed with soap and water like other oils.
Lycopodium is a spore and should not be inhaled. Students with allergic conditions must be alerted.
Materials for each student group
Oleic acid in dropper bottles
Large plant saucer (Approximate diameter 26 to 28 cm or larger) Small graduated 10 mL
Pitcher with tap water for filling plant saucer Disposable pipette (microtip) Measurement tape
Lycopodium powder (optional) for dusting the water surface to make oil spill more visible Calculator
MSDS for Oleic acid MSDS for Lycopodium
Instructional Process
Design
1. Begin the design/problem solving process by questioning and discussion.
Demonstration may be necessary to provide a visual prompt for students. Some questions and suggestions to prompt and lead students into the design process are shown.
What would happen if a drop of oil was placed on water? Relate to a real world oil spill that students may have observed, such as gasoline or oil film on a wet road. How can we find the volume of a single drop of oil? Review the process of drop calibration that students learned earlier by questioning. Allow students to articulate the process of calibration by using pictures or demonstrations.
2. Perform a demonstration of an oil drop on a large container of water. Arrange
students so that they can see the teacher demonstration. Fill a large plant saucer about 3/4th full with water.
Wait till there are no waves on the water surface and place a small drop of oil on the water surface.
3. Some questioning is needed at this point for students to conceptually connect the
volume of the oil drop to the thickness of the oil film. Some suggested questions are –
• What is volume of the oil drop?
The volume is the measured volume from the calibration process.
• If a single drop is placed on the water to create an oil spill, what is the volume of the oil spill?
The volume of the oil spill equals the volume of the oil drop. • What is the approximate geometric shape of the oil spill?
A cylinder (Rectangular solid is also acceptable if the oil spill has a rectangular shape. The formula used will differ from the responses shown below.)
• How can we use this information to find the thickness? Volume of the cylinder = π r2H
V and r can be measured and H can be calculated.
• Why is it important to determine the thickness of the oil spill?
Answers vary but the environmental implication of an oil spill is a likely response.
Oil
Teacher Guide - Essential Chemistry Investigations
4. Allow students enough time to develop their plan for investigation using the
available materials.
5. Monitor students as they work but allow students to create their own plan.
6. Allow students to share their plan for investigation. Question students and allow
students to talk about how they ensured accuracy and precision in the experiment.
7. Instruct students to review the MSDS for the chemicals used and discuss appropriate
safety measures for handling and disposal of the chemicals. Allow time for students to record the chemical safety measures to be followed.
8. Instruct students to review the plan for investigation and identify safety precautions
that will be necessary during the investigation. Allow time for students to record the laboratory and personal safety measures to be followed.
Investigate
9. Ask students to perform the investigation, record the data, then discuss and write
down calculations and conclusions. Monitor students and the learning process. 10. Allow student groups enough time to complete their investigations and complete their
results and analysis. Encourage small group discussions and collaborations. 11. In the applications and extensions stage students may need time and resources to
research areas of their interest. In this investigation, students may examine EPA regulations about oil disposal and/or spillage, effects on the ecosystem, effects on specific organisms, commercial issues of oil companies etc.
Report
12. Allow class time for student groups to share the results of their investigation, analyses, extensions, and applications. Peer student groups may be coached to assess the presentations.
13. Student work may be displayed physically or digitally for other students’ review.
Student Investigation Template
Title:
Question
Write the question for investigation.
Design/Plan
Investigation
Identify the purpose of your investigation and record it in the space below. Conduct your investigation. In the space provided, record - materials, experimental procedure, safety precautions, data, calculations, graph (if applicable), analysis, conclusions, and
application/extension of learning. Be prepared to discuss your procedure and results with the group.
Purpose
Materials
Procedure: (if different from your original design)
Safety
Data
Analysis and Conclusion
