An extraordinary classroom activity certain to provoke discussion of an important current social and health issue. Designed to simulate the transmission of the HIV virus through the transfer of “body fluids,” the activity is based on a simple chemical reaction involving a dramatic and unmistakable color change.
- Disease transmission
This activity invites participants to exchange simulated “body fluids.” All but one of the test tubes distributed is filled with water. The remaining test tube, “the carrier,” which will be randomly selected by a participant, contains a dilute solution of sodium hydroxide. Although dilute, this chemical deserves respect and prudent laboratory procedures should be followed—see Safety Precautions.
After participants have exchanged the simulated “body fluids” in their test tubes (using the pipets provided) the instructor will ask participants to place two or three drops of the phenolphthalein indicator solution into their tubes. Participants who have contacted the carrier, either directly or indirectly, are “infected” and will be surprised to see the “fluids” in their tubes instantly turn from colorless to a bright pink.
The number of exchanges each participant conducts and the number of tubes initially “infected” will determine the ultimate rate of “infection.” For class sizes of 30 or less, one carrier should provide a dramatic result. The instructor should direct a minimum of three exchanges per participant for smaller classes but no more than four for up to 35 participants. It is important that participants circulate throughout the room or between groups following each exchange—this will ensure that the same few people do not simply keep reinfecting each other. When repeating the exercise the instructor may wish to vary the number of exchanges, the number of initial carriers or even to instruct one or more participants to “abstain” from exchanging.
Participants should be cautioned at the outset to exchange fluids carefully to avoid spillage. Spills should be absorbed on damp paper towels immediately—see safety precautions. It is also possible for the pipet to fall into the test tube, in which case the student should not attempt to retrieve it with bare fingers or by tipping the tube. The instructor should retrieve pipets either with forceps or with gloved fingers. At no time should pipets be used by participants to “squirt” each other. The possibility of eye contact with dilute sodium hydroxide should be strictly avoided.
Phenolphthalein indicator solution, 0.5%, 3 dropper bottles of 30 mL each*
Sodium hydroxide solution, 0.2 M, 500 mL*
Water, tap, distilled, or deionized†
Pipets,Beral-type, extra large bulb, 35*
Culture tubes, 20 x 150 mm, 35*
Test tube brush*
Test tube rack*
*Materials included in kit.
†Note: In most cases tap water will work effectively. See Tips.
Sodium hydroxide solutions are corrosive; skin burns are possible; very dangerous to eyes; chemical goggles and chemical-resistant gloves are recommended. Phenolphthalein solution is flammable. Do not use near heat or flame; fire risk. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The “body fluids” solutions may be disposed of down the drain with excess water following Flinn Suggested Disposal Method #26b.
- Prepare by filling all but one of the number of tubes required approximately one-half full with clean tap, distilled, or deionized water. Fill the remaining tube (“the carrier”) to the same level as the other tubes with the sodium hydroxide solution. The carrier tube should appear exactly as the remaining tubes and randomly placed among them in the test tube rack.
- Tell the participants that in today’s activity they will be discussing what puts them at risk of HIV infection. They will start by participating in an exercise that will simulate how the virus is spread in and among a community. Urge them to carefully follow your instructions.
- Say “I am going to ask you to pick up a test tube with “body fluids” in it, and when I tell you to begin I would like you to circulate about the room and exchange names and information about yourselves with each other. If you would like to, simulate exchanging “body fluids” by filling your pipet with the fluid in your own tube and transferring it to the other person’s tube. You may wish to take turns doing this. (Participants should not feel that the exchange needs to go both ways. Give them the option of choosing.) When transferring fluid to the other person’s tube take care not to contact the inside of the other tube or its contents with your pipet. Take care not to drop the pipet into either tube. (You may wish to demonstrate ideal transfer technique as you give these instructions.) Move to another location and repeat this procedure two (or three) more times. Once you have accomplished this with three (or four) people, sit down. Begin now.”
- When all participants are finished with this step, say “Please walk over to the table where you will find dropper bottles of phenolphthalein. (You may wish to add an air of mystery to this step by rubber-banding “Solution X” labels to the dropper bottles and referring to it only as “Solution X.”) Carefully squeeze only two or three drops of this solution into your test tube. Observe what happens to your test tube and return to your seat.” Give them time to find their seats.
- “Now, those of you that have bright pink tubes please stand up. By exchanging body fluids you have come in contact with someone who has passed the HIV virus on to you. That’s how quickly the virus can spread from just one person. Only one of you picked up a test tube that had the “virus” in it.” Here you might explain that Solution X is an acid–base indicator that reacted with the sodium hydroxide “virus” to form the pink color.
- Have those participants who are standing sit. A couple of possible points for discussion:
- “How is the activity similar to the spread of HIV?” (The exchange of the test-tube “body fluids” is analogous to engaging in sexual intercourse or sharing hypodermic needles.)
- “What would be the responsible behavior if one were to engage in sexual activities?” (People should properly use condoms every time if they choose to be sexually active. Emphasize that the best protection against the HIV virus is abstinence.)
- Make available to your students, and yourself, information regarding up-to-date knowledge of AIDS and the HIV virus. Knowledge, understanding and frank open discussions of this issue are vital.
- A brush is provided for cleaning the test tubes between trials. Tubes should be thoroughly cleaned to remove all traces of sodium hydroxide and phenolphthalein which would otherwise interfere with the results when the exercise is repeated. The Beral-type transfer pipets may be used repeatedly if thoroughly rinsed with warm soapy water followed by several exchanges of clear water.
- In most cases tap water will work effectively. It would be wise to test a small quantity of your local tap water with one or two drops of phenolphthalein indicator solution prior to conducting the exercise. If any color change is detectable with tap water the activity will require distilled or deionized water. Distilled water from the grocery store is adequate.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Asking questions and defining problems
Developing and using models
Constructing explanations and designing solutions
Obtaining, evaluation, and communicating information
Disciplinary Core Ideas
MS-LS1.A: Structure and Function
MS-ETS1.B: Developing Possible Solutions
HS-LS1.A: Structure and Function
HS-ETS1.B: Developing Possible Solutions
Cause and effect
Systems and system models
MS-ETS1-1. Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.
HS-ETS1-3. Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics, as well as possible social, cultural, and environmental impacts.
Special thanks to Raleigh Philp, Associate Director of the Healthy Kids Region 8 Center, Downey, California, who provided us with the instructions for this activity.