Half the Chemistry class was gone yesterday, so they had to make up their experiment today. Well, one student of the students who did her work yesterday entreated me to lead her peers through the experiment. It was pretty awesome, because she had been struggling with the topic for the last week and had finally gotten it yesterday.
And she did an excellent job. She not only walked the rest of the class through the theoretical calculations, but guided them through the experiment itself.
Peer teaching works best when students are excited about what they’ve learned and want to share. I’m still trying to figure out the best way of inciting this excitement when I break the groups up for their projects. Giving them choice is important, but also, I think, giving them challenging work that they’re proud to accomplish.
Given the idea that “learning situated in meaningful contexts is often deeper and richer than learning in abstract contexts,” (Lillard, 2007), I’ve been trying to orient our robotics program toward developing devices that we can use at school. Not only can these devices serve a useful purpose, but their presence around the school can, perhaps, inspire other students to want to make their own.
To this end, one of our first practical projects is a timer (by Joe A.) for when students give their presentations in Chemistry class. For the last round of presentations they had 20 minutes, so I had Joe build the circuits and program the Arduino to make the green light to be on for 15 min, the yellow on for 4 min, the red for 1 min, and then the piezoelectric buzzer would go off for 5 seconds and the red light would start blinking.
Joe did an awesome job, and the timer worked remarkably well. I did what we wanted it to do, and it actually worked to help them keep their presentations under time.
A couple of my students asked for worksheets to practice drawing atoms and electron shells. I updated the Atom Builder app to make sure it works and to make the app embedable.
So now I can ask a student to draw 23Na+ then show the what they should get:
Worksheet
Draw diagrams of the following atoms, showing the number of neutrons, protons, and electrons in shells. See the example above.
Calibration curves produced by different student groups to determine the relationship between density and concentration of salt (NaCl) solutions.
To start with chemistry class, we’re studying the properties of substances (like density) and how to measure and report concentrations. So, I mixed up four solutions of table salt (NaCl) dissolved in water of different concentrations, and put a drop of food coloring into each one to clearly distinguish them. The class as a whole had to determine the densities of the solutions, thus learning how to use the scales and graduated cylinders.
However, for the students interested in doing a little bit more, I asked them to figure out the actual concentrations of the solutions.
One group chose to evaporate the liquid and measure the resulting mass in the beakers. Others considered separating the salt electrochemically (I vetoed that one based on practicality.
Most groups ended up choosing to mix up their own sets of standard solutions, measure the densities of those, and then use that data to determine the densities of the unknown solutions. Their data is shown at the top of this post.
Finding the mass of solution in order to calculate its density.
The variability in their results is interesting. Most look like the result of systematic differences in making their measurements (different scales, different amounts of care etc.), but they all end up with curves where the concentration increases positively with density.
I showed the graph above to the class so we could talk about different sources of error, and how scientists will often compile the data from several different studies to get a better averaged result.
Then, I combined all the data and added a linear trend line so they could see how to do it using Excel (many of these students are in pre-calculus right now so it ties in nicely):
Trend line from combined data.
What we have not talked about yet–I hope to tomorrow–is how the R-squared value, which gives the goodness of the fit of the trend line to the data, is more a measure of precision rather than accuracy. It does say something about how internally consistent the data are, but not necessarily if the result is accurate.
It’s also useful to point out that the group with the best R-squared value is the one with only two data points because two data points will necessarily give a perfectly straight line. However, the groups that made more solutions might not have as good of an R-squared value, but, because of the multiple measurements, probably have more reliable results.
As for which group got the most accurate result: I added in some data I found by googling–it came off a UCSD website with no citation so I’m going to need to find a better reference. Comparing our data to the reference we find that team AC (the red squares) best match:
The straight line shows my (currently) accepted values for the concentration/density relationship.
Bending the glass tubing is fairly straightforward, but looks awfully sciency.
Our steam distillation apparatus for extracting lavender oil started off fairly simply — a steamer connected to a glass tubing running under the cold water tap to a collection flask — and evolved from there. One of the final tweaks we attempted, was to make a coil in the glass tubing so the steam would have a longer transit through the ice-water bath to enhance condensation.
We heated the glass using a small butane burner until it became pliable, then bent the tube into shape around a piece of wet wood. Using the wood was not as effective as we’d hoped because the glass tubing is fairly thin and cools down quickly when in contact with the water.
You also have to be very careful when bending the tubing to make sure you don’t pull on it. Pulling stretches the glass, making the walls thinner, making it more likely to break. My students discovered this the hard way.
While steam distillation is the recommended method for extracting oils from herbs, we’re trying a quick an dirty method of simply heating up the lavender leaves in water (up to 40 ºC) and seeing if any of the oils float to the top. If this does not work, we’ll still have produced some lavender scented water for our soapmaking.
The lavender leaves came from the large bushes out by the preschool that the outddoor group trimmed for Ms. Dicker.
pH measurements from soil, bird manure, composted horse manure, and kitchen compost.
We’ve acquired a selection of manures and composts for revitalizing our orchard, but don’t quite know if they’re safe to add to the soil. Too much nitrogen in the manure will “burn” plants. Therefore, we tried a simple pH test as a quick-and-dirty proxy for estimating the nitrogen/ammonia concentration of the samples.
Since we’ve been working on the orchard, Dr. Sansone has contributed a pile of composted horse manure, a pile of composted kitchen scraps, and a pile of mixed compost and pigeon manure. You’re supposed to let bird manure compost for quite a while (months to years) before using it because of the high ammonia content that is produced by all the uric acid produced by birds.
The “burning” of the plants happens, primarily, when there’s too much ammonia in the manure. Ammonia becomes basic (alkaline) when dissolved in water (thanks to Dillon for looking that up for us). The ammonia (NH3) snags a hydrogen from a water molecule (H2O) making ammonium (NH4+) and hydroxide ions (OH–).
NH3 + H2O <==> NH4+ + OH–
The loose hydroxides make the water basic.
When excess amino acids are broken down the amine group becomes ammonia.
The ammonia, in this case, comes primarily from the breakdown of urea and uric acid in the manure. Animals produce urea (in the liver) from ammonia in the body. The ammonia in the body comes from the breakdown of excess amino acids in food. We get the amino acids from digestion of proteins (proteins are long chains of amino acids. The urea is excreted in urine, or in the case of birds as uric acid mixed in with their feces.
Experimental Procedure
Weigh 100 g of soil/compost/manure.
Add enough water to fill the beaker to the 300 ml level. Some of the samples absorbed significant amounts of water necessitating more water to get to the 300 ml level.
Stir to thoroughly mix (and melt any ice in the soil) then let sit for 5 minutes.
Pour mixture through filter (we used coffee filters).
Test the pH of the filtrate (the liquid that’s passed through the filter) using pH test strips.
Important Note: We did the experiment under the hood, because the pigeon manure was quite pungent.
In addition to testing the manure and compost, we tried a soil sample from the creek bank, and a sample of fresh pigeon manure to serve as controls.
Results
The results were close to what we expected (see Table 1), with the bird manure having the highest pH.
Table 1: pH of soil, manure, and compost samples.
Sample
pH
Topsoil from Creek Bank
6
Fresh Pigeon Manure
8-9
Kitchen Compost
5-6
6 Month Old Pigeon Manure/Compost Mix
6-7
Discussion/Conclusion
While the high pH of the fresh pigeon manure suggests that it probably too “hot” to directly apply, it was good to see that the composted manure had a pH much closer to neutral.
This is a simple way to test the soil, so it may be useful for students to do this as we get new types of fertilizer.
We’ve looked at the simple acid/base reactions that produce the carbon dioxide bubbles in chocolate-chip cookies, but this video goes over a number of other relevant chemical concepts and the temperatures at which changes occur, including:
Emulsions: butter is an emulsion that separates into its constituent fats and water at 92ºF,
