Ran some basic tests to get an idea of how well (or poorly) the use of dry ice and universal indicator would be for this lesson.
Instant Ocean mix (per mfg’s recs): 0.036g/mL
Universal Indicator (per mfg’s recs): 15μL/mL
Played around a bit with different solution volumes, different dry ice amounts, and different Universal Indicator amounts.
|Indicator Vol (mL)||Solution||Solution Vol (mL)||Dry Ice (g)||Time to Color Change (m)||Notes|
|3||Tap H2O||200||0.5||>5||Doesn’t trigger full color change and not much bubbling (not very exciting)|
|3||Instant Ocean||200||1.5||<0.5||Begins at higher pH than just tap water. Full color change is slower than just tap water, but still too quick for timing.|
|2||1M Na2CO3||200||5||>5||No color change and dry ice fully sublimated.|
|2||1M Tris Base||200||5||>5||No color change and dry ice fully sublimated.|
|2||Tap H2O + 20 drops 1M NaOH||200||5||2.75||~Same color as Na2CO3 and Tris Base solutions to begin. Dry ice gone after ~5m and final pH color is ~6.0.|
- Universal Indicator amount doesn’t have an effect. It’s solely needed for ease-of-viewing color changes. Use whatever volume is desired to facilitate easy observations of color changes.
- Larger solution volumes should be used in order to slow the rate of pH change, so that it’s easier to see differences in rates of change between different solutions.
- 1M solutions of Na2CO3 and Tris Base have too much buffering capacity and will not exhibit a decrease in pH (i.e. color change) from simply using dry ice. May want to try out different dilutions.
- Use of water + NaOH to match starting color of Na2CO3 and/or Tris Base is a good way to illustrate differences in buffering capacity to students.
- Overall, dry ice will work as a tool to demonstrate effect(s) of CO2 on pH of solutions!
Some pictures (to add some zest to this entry):