Title: To observe a carbon dioxide fountain
Aim(s): To observe the dissolution of carbon dioxide into alkaline hydroxide solution
resulting in a decrease in pressure and the creation of a fountain effect.
Target group: TY group
Equipment needed:
2 Retort stands, round bottomed flask, 500ml beaker, pinch clamp, two lengths of
rubber tubing (one of regular diameter and one piece with a very small diameter
tubing), glass tubing, filter flask, one large rubber bung to fit filter flask, one small
rubber bung to fit round bottomed flask, rubber bung borers, pinch clamp, small
funnel, plumbers tape, large deep water trough.
Chemicals needed:
Bromothymol blue indicator, 2M NaOH, “Alka Seltzer tablets”, H2O
Safety analysis:

Lab coats and gloves should be worn if available

Safety glasses must be worn at all times and long hair must be tied back

Any breakages must be reported immediately

Students should be familiar with procedure before carrying out experiment

It is essential that a round bottomed flask is used instead of flat bottomed
flasks such as Erlenmeyer or Florence flasks, as these flasks are unable to
stand the pressure difference produced in this experiment.

Carbon dioxide is not a dangerous gas and is safe to unlike ammonia, which is
also used to demonstrate the fountain effect.

2 M NaOH, poses the most danger in this experiment, and should be labelled
accordingly as highly corrosive.
Procedure:
1) Attach a 40 cm length of rubber tubing to the outlet of a 250ml filter flask.
The other end of the rubber tubing is placed in a 500ml round bottomed flask,
which has been filled with water and submerged in a large basin of water. The
CO 2 is collected under water.
2) Add 25ml of water and several “Alka-Seltzer” tablets to the filter flask. You
will need a rubber bung for the filter flask to prevent the gas evolved escaping.
Fill the round bottomed flask with carbon dioxide.
3) For the next step you will need a one hole rubber bung and a piece of glass
tubing which we go almost to the bottom of the round bottomed flask. At the
end of the glass tubing you should attach a 30 cm piece of very small rubber
tubing. The rubber tubing and glass tubing need to create air tight seal so
plumbers tape can be used to ensure that the gas does not escape.
4) Once the flask is filled with CO2, quickly stopper the flask with the one holed
bung and glass tubing. Use a pinch clamp to prevent the CO2 escaping.
5) Take a small funnel add 30 ml of 2M NaOH solution to the round bottomed
flask, close the pinch clamp immediately
6) Set up a retort stand and carefully invert the flask as in diagram.
7) Take a 500ml beaker and a 400ml of water with a few drops of bromothymol
blue indicator. Place this beaker under the inverted round bottomed flask and
ensure that the rubber tubing extends half way into the water/bromothymol
solution.
8) Open the pinch clamp and observe what happens.
Sample results/ observations:
Once the pinch clamp is opened the water and bromothymol blue solution flows into
the round bottomed flask, creating a fountain effect.
Conclusion:
A decrease in the pressure in the round bottomed flask is the driving force of the
carbon dioxide fountain.
Possible questions to ask:
What is causing the bromothymol and water solution to move up the glass tubing?
Why does the fountain eventually stop?
Can you think of others uses of this type of experiment?
Links to Irish curriculum:
Gas Laws
Physical Chemistry
Note:
For this experiment an airtight seal is required so it is essential that the exact
equipment is used, I have made several alterations to this experiment to ensure the gas
cannot escape. Do not attempt this experiment unless you have a good selection of
materials, i.e. several different size pieces of glass tubing and several pieces of rubber
tubing of varying diameter.
Reference:
Case, M. (2007) ‘Carbon Dioxide Fountain’, Journal of Chemical Education, 84(10),
1671-1672