Description:

Students study descriptions of indicators and the way they are used to identify acids and bases. Based on this information, they then determine if unknown solutions are acids or bases.

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

This task is designed to take students approximately 8-10 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

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 standards requires a subject 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.

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

General Instructions to the Teacher:

This task is designed to take most students 8-10 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 and Base Testing 1":

At this station students should have:

• Solution A (water)
• Solution B (acid)
• Solution C (base)
• Red and blue litmus paper
• Plastic reaction plate or transparency paper
• Phenolphthalein
• Permanent fine line black marker
• Dropper bottle
• Small plastic cup
• Water for cleaning
• Paper towels
• Goggles
• Waste container

Advance Preparation:

Stock Solution Preparation: (4 dropper bottles for each student- dropper bottles can be reused for each class):

• Solution A- water in dropper bottles labeled "A."
• Solution B- acid solution; dilute citric or ascorbic acid.

  If using purchased citric acid, follow manufacturer's directions for making a dilute solution. If using "Fruit Fresh," dissolve 3 teaspoons in 1500 ml of water. Test with litmus paper. Place in dropper bottles labeled "B."

• Solution C- base solution; dilute lime water (Ca(OH)₂).

  For best results, purchase just prior to the activity as lime water has a short shelf life. Place in dropper bottles labeled "C."

Materials Preparation:

• Label dropper bottles "A," "B," "C," and "phenolphthalein."
• For best results, fill phenolphthalein bottles just prior to the activity.
• Keep litmus paper in closed containers.
• Use a permanent marker or a photocopier to transfer the template onto transparency paper. Cut into strips. Discard strips after using.
• Alternative: purchase reaction plates (24 wells). Use flat sides of both tops and bottoms of reaction plates. Wash wells between uses.

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.

Extensions/Modifications:

• Variations of this task include Acid and Base Testing 2 and 3 with different degrees of structure.
• Acid and Base testing 1, 2, and 3 - Micro, with different materials