Patient Zero Set Up
Pre-Activity
1. Dilute about 50 ml of NaOH with 100 ml of Distilled
Water; if using HCl as your acid, dilute this as well.
2. Set up 2 rows of identical cups, each row numbered
from 1 to 15 (or how ever many people will be
participating – greater than 20 becomes too difficult
to track backwards)
3. Choose a random number, and fill both cups labeled
with that number with the NaOH solution. Remember
that number
4. Fill all remaining cups with the acid solution (HCl or
distilled water)
During the Activity
1. Have each participant take a cup from the first row
only.
2. Each participant will exchange fluids with 3 other
participants by pouring all their fluid into one cup,
then pouring half back. They must note who (what cup
number) they exchanged with and in what order.
3. After 3 exchanges, each participant should receive 2-3
drops of phenolphthalein. If the solution remains
clear, then that participant has not come in contact
with the base. However, if the solution changes color
to pink, then the participant either had the original
base solution or came in contact with it during one of
their exchanges. The darker the color indicates how
much base is in the solution.
Post-Activity
1. Have the students narrow down their “Patient Zero” to
3-4 cup numbers by systematically eliminating the cup
numbers that they believe were not the original source
of the infection (or the base),
2. Place 2-3 drops phenolphthalein in those numbers from
the second row of cups and observe if a color change
occurs in one of them.
3. If not, place drops in each cup down the entire row
until the base is found.