Chemistry PBL
-
Level I
Essential Investigations
Investigation: Acid Rain
Description
Students design and conduct a laboratory process to determine the effect of acid rain on hard water, soft water, and salt water. These three types of water are representative of naturally occurring water bodies such as river water, spring water, and sea water. The observation and analysis of their data will lead students towards societal issues and personal as well as civic responsibility. The context of this learning experience is towards the end of the chemistry course after the topic of acids and bases.
Learning outcome
• Plan and implement a laboratory investigation using safe practices
• Apply chemistry concepts and process skills to determine the effect of acid rain on 3 different water bodies.
• Make measurements with accuracy and precision • Use significant digits in measurement and calculation
• Relate the effects of acid rain to societal issues and personal/civic responsibilities
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. Prepare/collect the following solutions –
• 0.1 M H2SO4 Label this solution as ACID RAIN and place in dropper bottles for
dispensing to students. This will increase student safety in handling the acid. • Bottled mineral water can be used to simulate HARD WATER. Place in
labeled reagent bottle. (pH > 7.2 and [HCO3] > 350 ppm)
• Soft spring water can be used to simulate SOFT WATER. Place in labeled reagent bottle. (pH < 6.0 and [HCO3] < 25 ppm)
• Salt water 0.1 M (pH <7.0) • Distilled water
3. Provide chemicals for each student group.
4. After completing investigation, ask students to clean and put away the equipment in the proper location.
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.
Attention to chemical laboratory safety is essential as students will be using chemicals, and glassware. Instruct students to wear protective aprons and goggles throughout the investigation.
Acid rain should be handled with the same safety precautions as sulfuric acid. Sulfuric acid is severely corrosive to eyes, skin, and other tissues. Safe and cautious handling is necessary throughout the duration of the investigation.
Materials for each student group
3 Beakers – 100 mL Graduated cylinder 50 mL
Data collection tools (probes, interface, calculator /computer) pH probe
Distilled water Hard water
Salt water (1% Salt solution by mass) Soft water
Acid rain
MSDS for 0.1 M H2SO4 solution (ACID RAIN)
Instructional Process
Design
1. Provide some context for introducing the investigation by using background questioning related to student experience. For example;
How many of you have heard of acid rain? What is acid rain?
Do you know what is happening to the statue of liberty? Why do you think this is happening?
The topic of acid rain may also be introduced by using a picture of the statue of liberty or a news article relating to acid rain.
2. Present the challenge – to find the effect of acid rain on various types of water.
Ensure that students know the types of water and their sources in nature. Allow think time at every stage before soliciting student responses.
3. Allow students to discuss and come up with a plan.
4. If students are unable to come up with a plan, some prompting questions may help with the design/problem solving process. Some suggested questions are – • What is acid rain?
Acidic rain water is called acid rain.
• How does rain water become acidic?
Exhaust gases from automobiles, released gases from coal power plants and oil refineries dissolve in rain water to create acid rain.
• How do you know if a solution is acidic?
The solution will have a pH less than 7
• What should be the pH of plain water? pH = 7
• If acid rain is added to plain water, how will the pH change?
The pH of the water will decrease from 7 into the acidic range.
5. Allow students enough time to develop and record their plan for investigation. 6. Monitor students as they work but allow students to create their own plan.
8. Instruct students to review the MSDS for the chemicals used and discuss appropriate safety measures for handling and disposal of the chemicals. Tell students that the acid rain is mostly sulfuric acid and the MSDS of the acid should provide safety instructions for safe handling and disposal. Allow time for students to record the chemical safety measures to be followed.
9. 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.
10. If necessary, discuss correct laboratory procedure for this activity. A brief procedure or task list is shown -
Procedure:
• Ensure personal safety by wearing aprons and goggles.
• Set up the pH probe in interface with calculator/computer for data-collection. Set the mode for “Events with Entry” where the pH will be recorded for every drop of acid rain added.
• 1-Distilled water:
Take 50 mL of distilled water in a clean dry 100-mL beaker.
Place the pH probe in the distilled water, swirl gently, and start data-collection. When the pH stabilizes, collect this pH as the first data point for “0” drops of acid added.
Add 1 drop of acid rain to the distilled water and swirl gently. When pH stabilizes, collect the pH as the second data point for 1 drop of acid rain added. Collect 2 more data points for additional drops. Stop data-collection after a maximum of 3 or 4 drops. Save the data, and prepare the probe for the next data-collection. (Rinse the probe in clean distilled water,
place in storage solution, and rinse again with distilled water before using in test solution.)
• Repeat the same procedure with 2-soft water, 3-hard water, and 4-salt water. After each data-collection, make sure to save the data set and follow appropriate procedure for cleaning pH probe.
• Graph the data sets to obtain 4 different graphs. Examine the graphs to make inferences and draw conclusions.
Investigate
11. Ask students to perform the investigation, record data, then discuss and write down calculations and conclusions. Monitor students and the learning process. 12. Allow student groups enough time to complete their investigations and analyze their
results and analysis. Encourage small group discussions and collaborations. 13. In the applications and extensions stage students may need time and resources to
research areas of their interest. In this investigation, students may examine causes of acid rain, environmental effects, and prevention measures.
Report
14. 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.
15. Student work may be displayed physically or digitally for other students’ review. 16. At closure, students should be able to articulate the effects and hazards of acid rain in
their own words. Asking students to present and share their personal thoughts and concerns extends their understanding to the real world and emphasizes their own role in it.
17. Encourage discussion and debate among student groups about the environmental concerns of acid rain throughout the world.
Sample data and graph is shown below as a guide for the teacher.
Drops Distilled Water Soft Water Hard Water Salt Water
0 6.86 5.88 7.74 6.98
1 3.79 3.96 7.52 6.96
2 3.55 3.66 7.37 6.84
3 3.39 3.49 7.26 6.84
7.00
6.50
6.00
pH 5.50
5.00
4.50
4.00
3.50
3.00
0 1 2 3
Title:
Question
Write the question for investigation.
Design/Plan
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
