Acid base chemistry is always a popular topic. The struggle with this topic is that there is always so much a teacher can demonstrate. Demonstrations are great but it is tough at the end of the year when students are tired and time is precious. I did a couple of these demonstrations that students seemed to enjoy. I like these demonstrations because I will take any teaching moment that serves more than one purpose....especially at the end of the year.
The first demonstration involved a few drops of universal indicator and about 200 mL of tap water. Tap water in Ohio is slightly basic. I had the tap water with indicator in a beaker and a stir plate. I then added the candy "Toxic Waste". Yes...there is such a thing that students actually pay to ingest. Toxic Waste candy is rich in citric and malic acid. It tastes EXTREMELY sour (or so I am told). The acid is also just enough to change an indicator. See video 1.
Video 1: Natural Acid Base Indicator with Acidic Candy, ChemEd X Vimeo Channel, 5/31/2023.
There was a lesson on acid base chemistry, several changes in pH and a colorful reaction with a popular candy.
The next experiment was the Bromothymol Blue (BTB). Students are familiar with BTB. Most students used BTB in biology to detect carbon dioxide. A few drops of BTB in Ohio tap water is slightly blue. The BTB turns yellow if a person slowly and carefully bubbles their breath through the BTB solution. Many students did not realize that the BTB responds to carbonic acid that is formed from carbon dioxide in water. Pop Rocks are a popular candy that contains pressurized carbon dioxide. We put some Pop Rocks in with BTB and we could perceive a change in color. The next reaction showed a much more dramatic change in BTB. I placed a funnel with rubber tubing on the exhaust pipe of my car. I made sure to start the car with the garage door open and it was a cold start. I placed the rubber tubing in a clean 2 liter bottle for about 10 seconds. 10 seconds was enough to flush it with exhaust. I quickly capped it. The exhaust can stay in the sealed bottle for the day. I took a small drill bit, about 1/8 inch, and drilled a hole in a separate cap. (If you do not have a drill bit, simply use a hot nail in a bunsen burner and then use that to make a hole in the cap.) I take the cap off just before the experiment and put on the cap with the hole. Then I bubbled it through the BTB solution. The carbon dioxide quickly changes the BTB as seen in video 2. After the demonstration we then discussed some numbers concerning estimated volumes and gases in the air and the acidification of the oceans. It really gets student's attention.
Video 2: BTB Car Exhaust and Pop Rocks, ChemEd X Vimeo Channel, 5/31/2023.
Overall it was a fun, quick and applicable demonstration that tied real life chemicals, experiences and acid base chemistry together. Do you have a quick demonstration that you like? Please share!
For Laboratory Work: Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016).
For Demonstrations: Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations.
Other Safety resources
RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies