Curriculum Testing – Determination of Most Useful Concentration of Sodium Carbonate Solution

After evaluating whether or not dry ice would be effective to trigger a noticeable change in pH in a solution, I determined which concentration(s) of sodium carbonate (Na2CO3) would be most useful for demonstration and usage within the curriculum. Previously, I used a 1M Na2CO3 solution a the universal pH indicator showed no change in color. What I want is a color change, but one that takes place at a noticeably slower rate than the other solutions that are demonstrated/tested; this will show how sodium carbonate acts as a buffer to CO2-acidification.

Additionally, I tested the difference in rate of pH change between Instant Ocean and sodium chloride (NaCl). The reason for testing this is to use this as a demonstration that salt water (i.e. sea water, ocean water) isn’t just made up of salt. It’s likely that many students simply think of the ocean as salt water and have not considered that the makeup of sea water is much more complex.

Finally, I performed these tests in larger volumes than I did previously to verify that the larger volumes will slow the rate of pH change, thus increasing the time it takes for the universal pH indicator to change color, making it easier to see/monitor/time.

Instant Ocean mix (per mfg’s recs): 0.036g/mL (36g/L)

For the NaCl solution, I used the equivalent weight (36g) that was used to make up the Instant Ocean solution.

 

Results:

  • Use of 0.001M Na2CO3 is passable, but due to the fact that it’s a diprotic base, the pH indicator didn’t progress lower than ~pH 6.0 in my limited tests. Adding additional dry ice (or using an even more dilute solution) are options to drive the pH lower.
  • The comparison between salt water and Instant Ocean will work well as a demonstration to introduce the concept that sea water is more complex than just being salty.
  • Using 1L volumes works well to slow the color changes of the universal pH indicator to improve the ability of the students to observe and measure the rate of color change.

The table below summarizes what I tested.

SOLUTION VOLUME (mL) DRY ICE (g) TIME OBSERVATIONS
0.1M Na2CO3 1000 3.0 No color change. Dry ice gone.
0.01M Na2CO3 1000 3.3 No color change. Dry ice gone.
0.001M Na2CO3 1000 3.3 ~20s Dry ice gone, but final color indicated a pH ~6.0.
Instant Ocean 1000 3.3 3m Initial color change noticeable within 10s; full color change after ~3m
NaCl 1000 3.0 instant Immediate, complete color change.
Tap H2O 1000 3.3 3m pH started @ ~7.5. Full color change took place.

Curriculum Testing – Viability of Using Dry Ice to Alter pH

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 1.5 <0.5
3 Tap H2O 200 0.5 >5 Doesn’t trigger full color change and not much bubbling (not very exciting)
5 Tap H2O 1000 12 <1
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.

 

Summary

  • 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):

 

 

 

Teaching – OA Lesson Plan Development

I’m currently collaborating on tweaking/developing a lesson plan and corresponding curriculum to teach Washington high school students about the chemistry involved in ocean acidification.

This is a project that’s already been in the works and I’m being brought in to assist (or, take over?) with the development. I’m pretty interested and excited by this. The reason for my excitement is that I was in the secondary education program to become a certified secondary education teacher while I was in graduate school. So, this project lets me apply the knowledge I garnered about teaching science during that time.

The current state of the project has a lab protocol, but no real lesson plan for the teachers to utilize. The lab protocol, in my view, is a bit too dense for high schoolers to digest and is a bit too much of “do this, write down the number: that’s ocean acidification!” It currently lacks an important element of science pedagogy: discovery. My goals are to tweak the protocol in such a fashion that it is more engaging and, possibly, hypothesis-(i.e. discovery) driven. This type of teaching has been shown to greatly improve retention and help improve/develop critical thinking skills.

The lesson plan should have sufficient information for teachers to decide if the lesson is appropriate for them to teach (e.g. which Washington state standards are addressed, what learning level(s) does the lesson require, what materials/supplies are needed, etc.), if they have enough time to conduct the lesson, and if they have ample understanding of the topic to feel comfortable teaching it.

I’ve put this project on GitHub. It allows for active collaboration on projects. Although there are some hurdles for those collaborators who have not used the service before, I think there are some good organizational benefits that are worth dealing with the initial headaches that might come for beginning GitHub users.

One benefit to developing this project on GitHub is that all changes are tracked and a description of the changes are required when they are made. This makes it relatively to see what changes were made, by who, and when. Although using something like Google Docs also automatically tracks changes, it does not allow the ability to provide a comment when changes are made. Because of this, it’s not always clear why the change was made in the first place.

An additional benefit, and this is the main reason I think it’s best to develop this project on GitHub, is the Issues tracker (see screenshot):

 

The Issues section allows for targeted discussion of the project and eliminates the volleys of email that often happen on collaborative projects. It will keep all discussions about this project in a single location and won’t require exhaustive searches of emails that easily get buried during a work week. Additionally, the discussions can remain focused on specific topics without getting lost within a emails attempting to broach multiple topics at once.