- University of Virginia
- Physics Department
A Physical Science Activity
- Acid-Base Tea Party
Adapted from an activity in Macmillan's
Physical Science by Denise Eby and Robert B. Horton
2003 Virginia SOLs
Demonstration - Discrepant Event
- 500 mL 0.1 M solution of sodium hydroxide NaOH (4g NaOH in 1 liter of water)
- 6 mL of concentrated hydrochloric acid (HCl)
- Less than 1 mL of phenolphthalein
- 4 clear glasses
- 1 clear pitcher or 1000 mL beaker
- Prior to students reporting to class, set out the 4 glasses all in a row
and prepare your 0.1 M NaOH solution. Put 500 mL of NaOH in the pitcher or
the large beaker.
- Leave the first two glasses empty.
- Add just a few drops of phenolphthalein to the third glass.
- Add 6 mL of concentrated HCl to the fourth glass. (CAUTION: Do not let students
handle the fourth glass in any way!)
- When your students arrive, begin class by telling them "today,
we are going have a tea party."
- Begin pouring the NaOH solution into the glasses beginning
with first glass. Of course, nothing will happen in the first or
second glass. If students complain that the tea is clear, then
tell them "we are pretending."
- As you pour the "tea" into the third glass the phenolphthalein
will react and turn the "tea" pink. At this point you need to act
as if you are totally surprised by this turn of events.
- Begin with the first glass and pour the "tea" back into the
pitcher. Again as you pour the first two glasses back into the
pitcher, nothing will happen. When you pour the third glass of
pink "tea" into the pitcher, all of the tea will turn pink. Again
act surprised and say "Oh well, pink tea will just have to do."
- Start pouring the now pink "tea" into the glasses starting
with the first glass. When you pour the pink "tea" into the fourth
glass, the concentrated HCl will reverse the reaction with the
phenolphthalein and the "tea" will be clear again. At this point,
you need to act totally perplexed.
- Finally, pour the pink "tea" now in the first three glasses
back into the pitcher also containing pink "tea". Then pour the
clear "tea" in the fourth glass back into the pitcher of pink
"tea". All the "tea' turns colorless. Now your students should be
ready to begin their study of Acid-Base Chemistry!
This demonstration is designed to hook your students on acid-base chemistry.
It requires a little acting on your part as you proceed with your pretend tea
party. Be sure to keep your students back from the demonstration. Wear your
safety goggles. The demonstration can be done with more or less NaOH by adjusting
the amount of HCl used also. Because phenolphthalein detects bases, you can
use any amount over 6 mL of HCl and it will turn the whole pitcher clear again
by making the solution acidic, but you cannot use less than 6 mL or the solution
will remain basic and the color will still be bright pink.