If using a sunny window for light, experiments may take longer than 24 hours. The core inquiry activity entitled Bad Breath Test, might be used prior to the pre-lab activity to give students practice in using bromthymol blue. Do not provide the hypotheses and experimental setups to the students. Elements of a good science experiment Prior to this lab, give the students several experiences in following methods that scientists use to design and conduct experiments. Students should be grouped in collaborative teams of four to six.
Alternative strategies Have teams design experimental setups for more than one hypothesis.
To extend this investigation, have student teams create their own pond ecosystem models using terrariums or two liter. Students could experiment with water samples from their own ecosystem models and might also compare results with pond samples taken from a local outdoor area. Explain to the students that carbon dioxide acidifies water. The color of bromthymol blue is an indication of the presence or absence of carbon dioxide in a water sample. Carbon dioxide can introduced it to a water sample by exhaling through a straw then using the bromthymol blue indicator solution to test for acidity.