EXPERIMENT 7: Spread of Contagion

Read the entire experiment and organize time, materials, and work space before beginning.

Remember to review the safety sections and wear goggles when working with chemicals.

Allow 60 minutes to perform this experiment

Objective: To demonstrate the ease in which contagion is spread

Materials: Student provides: Assistant(s), 1 minimum and up to 7 if possible

Distilled water (DO NOT use tap water)

From LabPaq: 50-mL Graduated cylinder

Clear plastic cups, 8

Scissors from dissection kit

Experiment Bag: 30 mL 0.1M Sodium hydroxide

Pipet with 2 mL of phenolphthalein

Discussion and Review: Contagious diseases can spread rapidly through a group of

people from very little contact. Many germs thrive in water or moisture and can spread

rapidly from contact such as drinking from the same glass or eating from the same

plate. This experiment demonstrates the speed with which such spread of contagion

can occur.

The experiment requires at least one assistant and preferably 7 assistants. The more

the better! Try to do it when you can arrange to have a group of people who are willing

to help you and who can all get together at the same time. Or you can simply call

friends and/or neighbors and ask them to come over at a specific time to assist you with

a science experiment. If you have everything set up ahead of time, the experiment

should not take more than 10 minutes of their time. This is a great experiment that will

impress your friends, so don’t be embarrassed to ask for their help.

Your assistants can be any age. The only criterion is that they be able to understand

and exactly follow the directions you will give them. The most important direction will be

that they must NOT drink the solutions used in this experiment! If it is impossible

for you to gather a group of people to help you, the experiment can be done with just

one assistant by following the alternate instructions in step 10 of the procedures.

PROCEDURES:

1. Read through all the procedures below and form your hypothesis as to how many of

the glasses will indicate contagion at the end of the experiment.

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2. Set up the experiment a few minutes before you plan to perform it. Your assistants

should not be in the same room, or should have their backs turned so they cannot

see what you are doing during this set up.

3. Line up the 8 clear plastic cups from the LabPaq along a table or counter. There

should be 1 clear plastic cup for every participant including you. Use 8 cups

regardless of how many assistants you have.

4. Empty the contents of the bottle of sodium hydroxide (30 mL) into one cup.

5. Use the graduated cylinder to measure and pour exactly 30 mL of distilled – NOT tap

– water into each of the remaining cups.

6. Place scissors, pencil, and paper in a convenient place for when you need them.

7. Ask your principal assistant to rearrange the cups while you turn your back or leave

the room.

8. Then have the principal assistant turn away while you rearrange the cups again.

The sodium hydroxide is clear and odorless. The objective is to make sure that no

one, not even you, knows which cup it is actually in.

9. Call all of your assistants together and read them the following instructions:

We are going to pretend that we are at a party and enjoying these “beverages.”

Each of us will be responsible for one glass after I have finished explaining the

procedures.

Do NOT, I repeat, DO NOT DRINK any of the “beverage” solutions or you could get

very, very sick and have to go to the hospital! Remember, this is pretend!

You are going to pretend to mingle at a party and consecutively exchange

“beverages” with 3 different people.

Pour the “beverage” solution from your glass into another person’s glass while being

very careful to not spill any. Then that person will very carefully pour half of the

combined “beverage” solution back into your glass.

Do this same exchange with two other people – 3 in total. After you and your glass

have exchanged “beverages” with 3 different people’s glasses, place your glass on

the table or counter and stand next to it.

10. If you do not have many assistants, you and the assistant(s) you do have can act the

parts of other imaginary assistants by taking each of the glasses and going through

the exchange process with three other glasses. Be sure that each glass has

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exchanged with three other randomly selected glasses before the next glass begins

its exchange.

11. Ask these questions of the assistant(s) and record the responses:

* One person at our party has a cold; do you think you caught this person’s

cold? If you feel 100% sure you caught this person’s cold, raise your hand.

* How many people at our party do you think caught this person’s cold?

12. Snip off the tip of the pipette of phenolphthalein and carefully

dispense 3 drops of phenolphthalein into each glass as shown at

right and observe what happens.

13. Now tell your assistants: “At the beginning of this experiment

before we began to mingle and exchange ‘beverages,’ one glass

contained sodium hydroxide, a clear chemical that reacts with

phenolphthalein. That glass represents a cold or any other

contagious disease. If your ending ‘beverage’ reacted to the

phenolphthalein that means you caught the cold or other disease.”

14. Ask your assistants if they were surprised by the results of this

experiment. Encourage them to express their thoughts about the

experiment, its results, and what those results mean.

15. Pour all the “beverages” down a sink and flush with running water. Either throw the

plastic cups away or wash them with soap and water and keep them for future use.

Questions:

A. What happened when the phenolphthalein was dropped into the cups?

B. Were your assistants surprised by the results of this experiment? Why or why not?

C. What where some of the comments they made?

D. Did this experiment confirm your initial hypothesis? Why or why not?

E. What do the results of this experiment suggest to you? How is the experiment a

model of the way in which real contagion can spread?