IS 220 Class 11 (2/2/2005)
Carbon dioxide has been a major "character" in the life processes we've studied. Today we'll get to know it more closely, and test some of our ideas.
Materials
- Seltzer, water
- Clear cups, straws
- Bromthymol blue (indicator dye)
- Hotpot
- NaCl (cubic crystals)
Activities
(DON'T FORGET TO TKE A CLASS PHOTO!)
- Demo to class of color change as way of detecting carbon dioxide
- water alone: no change
- seltzer (water plus what??): what happens?
- blowing through straw - supports (BUT DOES NOT PROVE!) our belief that we breathe out carbon dioxide
- Teach them (with demo) how to use a straw to count drops for a titration
- Prepare before class 2 diluted soda solutions: one hot, one cold
- Distribute glasses, indicator, straws for titration and have them test diluted soda
- Record procedure (draw or write), make & record observations, draw & record hypotheses
- Have them put a few crystals of salt into full-strength seltzer & watch and record
- Repeat for boiled seltzer & watch and record
- Remind 'em of hot water dissolving salt - relate, solicit explanations of differences
- Relevance for animals in the sea
Wrapup: the ocean dissolves not just salt but also gasses, CO2, and O2 - very important for respiration! We've investigated some features of this today.