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 assess 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 10-15 minutes to complete.

Overall Task Content Area:

Physical Science

Specific Knowledge Areas:

Properties of matter

Performance Expectations:

• conducting investigations
• using equipment
• gathering, organizing, and representing data
• formulating conclusions from investigational data

National Science Education Standards:

8 B PS 1: Properties and changes of properties in matter: Grades 5-8
1.2 Substances react chemically in characteristic ways with other substances to form new substances (compounds) with different characteristic properties. In chemical reactions, the total mass is conserved. Substances often are placed in categories or groups if they react in similar ways; metals is an example of such a group.

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 10-15 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 and Basing Testing 1 - Micro":

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
• Disposal pipettes
• Cassette case
• Small plastic cup
• Water for cleaning
• Paper towels
• Goggles
• Waste container

Advance Preparation:

1.  Stock Solution Preparation:

• Solution A - water
• Solution B - acid solution; dilute citric acid (ex. - Fruit Fresh ^TM dissolved in water).
• Solution C - base solution; dilute lime water (Ca(OH)₂₎.

2.  Materials Preparation:

• Label dropper pipettes "A," "B," "C," and "Phenolphthalein.
• Pour individual stock solutions in small plastic cups. To fill pipettes, place a handful of pipettes into the solutions (tips down), and squeeze bulbs simultaneously. Capillarity will keep solutions in the pipettes without sealing.
• For best results, fill phenolphthalein pipettes just prior to the activity.
• Pipettes will fit inside of the cassette case with tips up for easy storage and handling. Styrofoam can be used as spacers between pipettes.
• Pipette Source: Specialty Transfer Pipettes (1 ml, 43 drops/ml)
• For best results, keep litmus paper in closed containers.
• Use the permanent marker or a copy machine to transfer the attached template onto the transparency. Use the smooth side of the transparency to avoid contamination. Discard after use.
• Alternative: purchase reaction plates (24 wells). Use flat sides of both lids and bottoms of reaction plates. Wash between uses.

Safety:

• Students must 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