Demonstrations Page 5 - Acids, Bases, and Indicators

Scroll down to view photographs and short descriptions of some of the demonstrations in the list below.

WARNING – Use at your own risk! We cannot guarantee the accuracy or the safety of these activities.  Some of these activities are far more dangerous than others. The contributors and Bradley University do not assume any responsibility for these activities or their results.  If you have questions, corrections, or comments please do not hesitate to contact Dean Campbell ( at Bradley University.

Ferrofluid Demonstrations
Refrigerator Magnet Demonstrations
Polydimethysiloxane Demonstrations
LEGO® Brick Chemistry and Nanotechnology Demonstrations
Seltzer Popper Car
This is a rocket car that uses the pressure from chemical production of carbon dioxide as the basis for propulsion. The carbon dioxide is produced by reaction between acids and carbonate salts. The picture below shows a rocket car based on the popular demonstration involving water and AlkaSeltzer® in a 35 mm film canister placed on a chassis made from LEGO® parts. The "fuel" for the popping canister demonstration is approximately half an AlkaSeltzer® tablet, which is placed into a 35 mm film canister (Fuji-brand film canisters seem to work best). Water is added to the canister (to fill it approximately one third to one half full) and then the canister is capped. Ordinarily in the demonstration the canister is placed upright. The citric acid and the sodium hydrogen carbonate in the AlkaSeltzer® dissolve in the water and react to produce carbon dioxide. When pressure builds up, the cap pops a couple of meters into the air and spits out a quantity of fizzy water. The picture below shows the canister taped to a frame made of LEGO® parts. A popping canister will push a car made with this set of parts forward 10-20 cm. Other combinations of parts may produce cars that can move further. The challenge is to make a chassis that is lightweight, but with a wide wheel base to prevent tumbling. You are welcome to send alternative designs to me at WARNING: The canister cap will fly backward with considerable speed, so a barrier to stop the cap is recommended. (The water will also spill out of the canister when it pops open.)
BELOW: A seltzer popper car.
Thanks to Karen Campbell for passing information about this canister demonstration from an early childhood education conference to me and to Kristine Campbell for assistance with testing the car. See Demonstrations Page 9 - Geology for related demonstrations, Seltzer Popper Volcanoes. More demonstrations involving LEGO® bricks may be viewed at the site "Exploring the Nanoworld with LEGO® Bricks."
Popcorn Rocks
When dark limestone (calcium carbonate) or dolomite (calcium magnesium carbonate) is barely submerged in vinegar (acetic acid solution) and the vinegar is allowed to slowly evaporate to dryness, white popcorn-looking crystals (calcium acetate?) grow on the surface of the rock. I have seen these rocks for sale in stores; I found mine in a park. I have seen an article (in the Journal of Chemical Education?) describing the chemistry of this process. If anyone knows the reference could you please let me know?
BELOW: Popcorn rock surfaces without (LEFT) and with (RIGHT) "popcorn" crystals.
pH Sensitivity of Colorants in Flower Petals
Many compounds in plants are pH sensitive and can be used as acid/base indicators (Shakhashiri, B. Z. Chemical Demonstrations; The University of Wisconsin Press: Madison, WI, 1989; Volume 3, pp. 50-57). For example, there have been many lab experiments using red cabbage as a pH indicator. Some flowers can also be used to determine the pH of a substance, and below you will see a few examples of this. We found that pink or purple flowers showed a large color change, but yellow flowers such as daffodils and dandelions did not.
1. Samples were cut into small pieces and placed into three test tubes labeled H+, neutral, and OH-
2. A small amount of water was added (about 2-3mL)
3. 4-5 drops of concentrated hydrochloric acid or 50% sodium hydroxide was added and the test tube was mixed
LEFT: Quince RIGHT: Red Tulip
LEFT: Daffodil RIGHT: White Lilac
LEFT: Dandelion RIGHT: Redbud Tree
LEfT: Rhodadendron (fresh) RIGHT: Rhodadendron (year old)
LEFT: Apple Blossom RIGHT: Wild Geranium
LEFT: Yellow Iris RIGHT: Purple Iris
LEFT: Purple Carnation (dyed) RIGHT: Phlox (Sweet Williams)
LEFT: Red Cabbage RIGHT: Bee Balm
LEFT: Peony (outer petal) RIGHT: Peony (inner petals)
Other references:
Kanda, Naoki; Asano, Takayuki; Itoh, Toshiyuki; Onoda, Makota. Preparing "Chameleon Balls" form Natural Plants: Simple Handmade pH Indicator and Teaching Material for Chemical Equilibrium, J. Chem Educ. 1995 72 1131.
Huntress, Ernest H. The Chemistry of the Red and Blue Pigments of Flowers and Fruits. J. Chem Educ. 1928 5 1392, 1615.
Geissman, T. A. Flower Coloration. J. Chem Educ. 1941 18 108.
Dyeing Seashells with Blackberry Juice
Seashells can be dyed by soaking in blackberry juice. The shells below were soaked in crushed blackberries for about a half hour. Shells that have abraded surfaces tend to turn bluish. I interpret this as the exposed aragonite (calcium carbonate) having a surface with a basic pH and turning the anthocyanins in the juice blue. Some shell surfaces that are not abraded and still have a sort of a "skin" can turn reddish. I interpret this as the anthocyanins remaining at a more acidic pH as they soak into this "skin".
LEFT: Undyed shells. RIGHT: Dyed shells.

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Last updated 1/18/12

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