Description:

Students study descriptions of pH and determinations of acids and bases. Based on this information, they then determine which unknown solutions are more acidic. These inferences and data given from previously recorded rainfall are used to identify which sites receive the most acid rain and the affects this may have on wildlife.

The task assess students' abilities to make simple observations, apply their observations to test an unknown, and make generalized inferences from their observations and apply their understanding to an everyday situation.

This task is designed to take students approximately 8-15 minutes to complete.

Overall Task Content Area:

Physical Science

Specific Knowledge Areas:

Properties and changes of properties in matter

Performance Expectations:

• conducting investigations
• using equipment
• gathering, organizing, and representing data
• formulating conclusions from investigational data
• applying scientific principles to develop explanations and solve new problems

National Science Education Standards:

8 A SI 1: Abilities necessary to do scientific inquiry: Grades 5-8

1.4 Develop descriptions, explanations, predictions, and models using evidence. Students should base their explanation on what they observed, and as they develop cognitive skills, they should be able to differentiate explanation from description- providing causes for effects and establishing relationships based on evidence and logical argument. This standard requires a subject matter knowledge base so the students can effectively conduct investigations, because developing explanations establishes connections between the content of science and the contexts within which students develop new knowledge.

1.8 Use mathematics in all aspects of scientific inquiry. Mathematics is essential to asking and answering questions about the natural world. Mathematics can be used to ask questions; to gather, organize, and present data; and to structure convincing explanations.

8 C LS 3: Regulation and behavior: Grades 5-8
3.1 All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment.

(Use the "hot" link on the PALS home page to check the full text of related National Science Education Standards, if desired.)

National Council of Teachers of Mathematics:

Algebra (AL1): Understand patterns, relations and functions.

Data Analysis and Probability Standards (DAP3): Develop and evaluate inferences and predictions that are based on data.

Problem Solving (PS2): Solve problems that arise in mathematics and in other contexts.

General Instructions to the Teacher:

This task is designed to take most students 8-15 minutes to complete.

Students will be working individually for the experiment/activity part of this exercise.

The materials should be set out at each lab station, if possible. A central supply area, if needed, should be easily accessible. All supplies should be clearly labeled.

Materials for "Acid Precipitation":

At this station students should have:

• Citric acid (Fruit Fresh^TM)
• Stock bottles
• Permanent fine line black marker
• Water
• Dropper bottles labeled A-D
• pH paper (range 2-8) in vial with color key
• Transparency test card
• Paper towels
• Water (550 ml)
• Waste container
• Safety goggles
• Water for cleaning

Advance Preparation:

Stock Solution Preparation:

• The solutions can be purchased as buffer solutions from a science supply company.
• If you are making your own solutions, use citric acid crystals (Fruit Fresh^TM) which are less toxic than other acids.
• You might use the following chart to make enough stock solutions to fill 30 student dropper bottles with 50 ml each.

For Best Results:

• Test each solution with pH paper strips prior to use.
• It is difficult to maintain a pH of 7 in a stock solution. Atmospheric CO₂ will lower the pH upon exposure. Keep bottle tightly covered and adjust pH as needed by adding drops of a weak base such as lime water to baking soda solution. (Add cautiously and test often with pH paper.)
• Transfer attached template for testing card with a permanent marker or a copy machine. Use shiny side of transparency to avoid contamination between tests.

Safety:

• Students should wear safety goggles.
• Check MSDS (Materials Safety Data Sheet) for further laboratory precautions.
• Laboratory safety procedures required.
• Be careful.
• Teachers and students should always exercise appropriate safety precautions and utilize appropriate laboratory safety procedures and equipment when working on science performance tasks.