Stop!! -- Go!!
(The traffic light demonstration)
- 250-mL Erlenmeyer flask
- Rubber stopper
- 100-mL 1.0 M NaOH
- 10 mL indigo carmine solution (1%)
- 100 mL dextrose solution (0.133 M)
Caution: Eye protection should always be worn when handling chemicals. Adult supervision is required.
Place a 100 mL of NaOH and 100 mL of dextrose solution into a 250-mL Erlenmeyer flask. Add 10 mL indigo carmine solution.
Let solution sit until amber. DO THIS SETUP BEFORE THE SHOW!
Shake gently. The solution will turn red. Shake vigorously. The solution turns green.
If it becomes difficult to achieve the green color, unstopper the flask and let some air in. Than continue as before.
You are flipping between oxygenated and deoxygenated states of indigo carmine. Each structure absorbs and transmits light in a different part of the spectrum.
----Contributed by Jackie Stewart, Mark Twain Section