Sunday, October 27, 2019

Best Mole Day Yet!

Hands down, this year was the most fun mole day of my teaching career. My students embraced the "mole day celebration item" assignment (yes, it's mandatory fun) with creative, entertaining, and delicious creations. We celebrate the mole on October 23rd, of course. Here are a few of the highlights.
Avogadro's number cookies

mole cupcakes

mole day trivia game

mole-tzart, a first for mole day

mole bowling, another first and very fun

an original mole day board game

moles in space demo, a great finale to mole day

mole cookies

a mole cake

surprise visit from these little people on mole day

mole day t-shirts

a 3-D printed mole made from one mole of material

origami mole


illustrated mole equivalencies

fun mole pun

delicious mole day brownies

Mole day tap dance, another first for mole day

Monday, October 14, 2019

Reworking the Qualitative Analysis and Bonding Lab

Test for the melting point above 500 C.
I have redesigned the Qualitative Analysis and Chemical Bonding (QA) lab to increase student success in identifying an unknown substance.  This lab comes from the Flinn AP Inquiry Lab for Big Idea 2, Investigation #6.  I ran the introductory activity as written in the Flinn lab on the first day; students make observations of representative substances to differentiate between ionic, non-polar, polar, and metallic substances. The changes came in the second day of the lab when I introduced the unknowns. In the AP lab, the goal is to use their QA flow chart to determine the bonding in their unknown substance and then work as a class to match up the substances to a possible list. In past years, the results for the second phase of the lab were not very satisfying because my students did not have enough experience  to design tests for the possible substances. This year I created a list of suggestions/notes that would help direct the students toward confirmation tests that would help them either confirm the identity of their unknown or rule out some possibilities on the list. I modeled the changes after Steve Sogo's lab style in which students can do a lab at almost any level of chemistry experience. The addition of the suggestions was a great improvement to the outcome, especially with the lab occurring in the first month of school when my students have very little experience in the lab. Most of the students were successful in identifying the bonding and the identity of their unknown, and they learned some new lab techniques in the process.
Recording evidence about the unknown for the video CER.

I've been doing this lab for several years with my AP Chemistry class in the spring as part of our AP review. Last year I decided to move it to the fall to accompany the nomenclature unit. It's a nice fit with the introduction to ionic and molecular compounds, and let's face it, there aren't many labs about nomenclature rules. The problem with moving it to earlier in the year is the very limited lab experience my students have in September. At Woodstock Academy, I teach AP Chemistry as a one-year combined honors/AP course. My students come to me in the fall with no chemistry, and they sit for the AP test in May. The QA and Bonding lab was only their third lab of the year.

The lab starts with a study of the properties of a representative ionic, non-polar covalent, polar covalent, and metallic substance. They test solubility, conductivity, and melting point. These are simple tests that inexperienced students can handle, allowing them to learn a few new techniques and practice lighting the bunsen burners. The students use their observations to develop a qualitative analysis flow chart to asses the bonding in an unknown substance. I dedicated a full lab day to the introductory activity because these students have only been in the lab twice so far this year. Everything takes longer when they are doing it for the first time and they work so cautiously in September! We had two regular class days before the second day of this experiment. I dedicated some class time for the lab teams to create their flow charts together. This was time well spent. My kids went back into the lab on the second day with a plan. Up to this point the lab procedure follows the Flinn AP inquiry lab kit procedure.

The changes came in the unknown identification. I've tried this lab for several years, each time with frustrating results. I would watch kids flounder, wondering why they didn't think to test the pH of the solution to see if they had citric acid, or why they didn't just do a flame test to see if it contained sodium. I basically had to tell students how to test for each substance and then what they should expect from each unknown. Very few of the kids were able to determine the identity of the unknowns, even with a short list of possibilities. I knew that something had to change.

Testing for decomposition at high temperature.
My goal was to give the kids a way to successfully identify their unknown substance from a list of possibilities that would work with limited chemistry experience. First I took a closer look at the twelve unknowns that came in the kit. I expanded the list of unknowns to include a few more ionic compounds with distinctive flame test colors, more non-polar compounds with very different melting points, and sand for a network solid. Next I started to develop some "hints/suggestions" that would lead the students toward tests that to confirm the identity of their unknown. The suggestions were designed to compliment the flow chart, not replace it. I still wanted the students to use the QA scheme as the basis of their work. Some of the suggestions were general like "ionic compounds that contain Na, K, Ca, and Li have distinctive colors when burned, use the flame test station if you want to test for this property". Other suggestions were very specific like "when heated, glycine produces ammonia gas, test for ammonia by inserting a moist piece of pH paper into the mouth of the test tube after heating the sample". During the course of the lab we discovered another lab hint to include that would provide a confirmation test for iron(III) oxide in addition to the distinctive color. One group was testing the melting point with the burner and found that it turned black. Curious. Well, of course, iron(III) oxide decomposes to iron(II) oxide when heated. I added this to my suggestion list for next year.
Testing melting point in boiling water.

My inspiration for these improvements came this summer at ChemEd when I spent some time with Steve Sogo. I was so happy to reconnect with him and catch up on his new projects. Steve has a gift for creating labs that are teaching events that include lab techniques and the chemistry necessary to solve a problem. I went to his workshop at ChemEd and got several great ideas for what I call "challenge labs" for this year. I talked over my dilemma about this QA lab with Steve. He helped me brainstorm so possible directions to go with this lab to incorporate enough chemistry to turn this into a learning event. The results were good this year. Most of the kids were able to confirm the identity of their unknown substance with tests for physical and chemical properties using the suggestions. Many of the kids said they enjoyed the lab and felt confident in their final answer. Each student created a video CER to justify the identity of their unknown. More about that process in the next post.

Sunday, September 29, 2019

Go Fish (for acids)

Go Fish for Acids!
Sorry I've been off the grid for so long. I'm ready to get back into this space again.

Students using the stir bar retriever to catch an acid fish.

Have you suffered through teaching acid nomenclature? It can be pretty rough. I've changed my approach completely and it really works. This year I passed out a set of acid matching cards to each student. The cards consist of about 20 names of acids and their corresponding chemical formulas on two difference colors of card stock. Starting with the chemical formulas, I have them sort the acids into binary and oxyacids. I write a brief definition of each on the board along with the naming rules for each type. Then I ask them to use the rules to match the correct name with each acid. By using the rules and a list of polyatomic ions, they can complete the task with success. Then I have them "Go Fish for Acids". I made up a set of "acid fish" from the names and chemical formulas. I cut out crude fish shapes from construction paper and taped the names and chemical formulas of the acids on them. I put a paper clip on each fish and threw the whole mess into a fish tank. The kids use the magnetic stir bar retriever (I call the magic wand, or fishing pole in this case) to catch an acid fish. They take the fish to their seat, write the name or chemical formula on their white board, and then check it with me. They cycle through the fishing about five or six times until I feel confident that everyone has had enough practice. It's really fun and interactive. And it works.

Tuesday, March 14, 2017

Colligative properties are BACK!

Snowy Day in New England
Winter in New England is the perfect time to teach colligative properties. The snow plows are out nearly every week prepping the roads for another winter storm, coating everything with rock salt. Ah Ha! Freezing point depression in action.

I brought back colligative properties this year because it is in the UConn ECE curriculum. Even though the topic was removed from the AP Chemistry curriculum in the recent overhaul, the undergraduates at UConn are required to learn it so we are too. I was secretly dreading it. However, the addition of a freezing point depression lab into our schedule made it all worth it. And, thanks to Flinn, I found a few fun demonstrations for class discussion that helped to bring this mini-unit to life.

Freezing Point Depression Lab
I spent a lot of time preparing for the freezing point depression lab. I poured over the pages from the UConn lab manual, trying to adapt the procedure to the equipment and chemicals I had available at my school. This lab presented the perfect opportunity to learn how to use the Bluetooth Vernier temperature probes that my students can run from their iPads. With only minor adjustments to the procedure, an excellent pre-lab video I found online (prelab video link), and some email exchange with the lab technician at UConn, we conducted this experiment with great success. Our cooling curves were absolutely gorgeous! Never mind that the melting point of our pure solvent was not exactly accurate, more to discuss in the error analysis. We didn’t have any of the unknowns that the technician recommended for the lab, so I bought a box of (smelly) moth balls from Lowes to use for our “unknown”. The lab turned into an analysis of the technique rather than an identification lab. With our beautiful graphs, the analysis was straightforward. About half the students calculated the molar mass of the moth balls to within 10% accuracy. Not a rousing endorsement for this technique, but still a valuable lab experience that I plan to do again next year.

These students are watching their solutions freeze.

One thing I loved about the lab was the “meta-lab” experience. To record the freezing point of the solution, the students had to make an ice/salt mixture for the cold bath. They had to use the freezing point depression of water to study the freezing point depression of cyclohexane. Boom! That’s my students’ minds blowing in lab.

Ice Cube Challenge!
In addition to the freezing point lab, we did several fun demos in class related to colligative properties and solubility. The first one was the classic “lift the ice cube with a string” challenge (Flinn Scientific Publication No. 91359). Using only salt and a string, I challenged my students to  lift an ice cube off the table without touching it. It’s harder than it looks! The salt melts the ice cube just enough to freeze the string to the ice cube. It’s delicate work.

I also used the classic demonstration of the conductivity of electrolytes with the light bulb conductivity tester. This quick and easy demo shows student how to identify an ionic compound from a molecular compound, and the difference between a strong and weak electrolyte. But, this year I added another wrinkle to the demonstration. Using a solution of lime water (saturated calcium hydroxide), I attempted to “blow out” the light bulb by bubbling carbon dioxide through the solution (Flinn Publication No. 91353). This reaction was a great review of precipitation reactions, and a way to give another tangible observation to go along with the cloudy product formed. The students could see the ion concentration decrease as the light grew dimmer, while simultaneously watching the solution get more cloudy from the insoluble calcium carbonate formed.

Look at the solubility of gases at three different temperatures.
Solubility of gases is a tricky topic to throw into the mix when learning about solutions. Just when my students are getting the hand of solubility trends, I added gases which are completely opposite from solid solutes. I used a simple, yet effective, demonstration of the solubility of carbon dioxide at three different temperatures to help them understand the trend. Using a can of soda and three water baths, I showed the kids how a higher temperature causes a gas to come out of solution faster (Flinn Scientific Publication No. 91457).

Solubility of gases is a tricky topic to throw into the mix when learning about solutions. Just when my students are getting the hand of solubility trends, I added gases which are completely opposite from solid solutes. I used a simple, yet effective, demonstration of the solubility of carbon dioxide at three different temperatures to help them understand the trend. Using a can of soda and three water baths, I showed the kids how a higher temperature causes a gas to come out of solution faster (Flinn Scientific Publication No. 91457).

Super Cool Demo!
I added another fun demo to the list, even though it was a little bit of a side step from the topic. All the kids have seen videos on YouTube of water bottles freezing while being poured. The trick is to make the water super-cooled in the freezer; a very delicate state that takes the liquid below the freezing point but still in the liquid state. This can only happen with liquids that are packed under pressure. I decided to try this supercool demo with my students, (Flinn Scientific Publication No. 91605). I used small bottles of club soda that I chilled in the refrigerator overnight. To make the super-cooled liquid, I made an ice/salt bath (freezing point depression again!) to cool the soda to -8 degrees for 10 minutes. I tried this demo three times, and I only got one good freezing event to happen. The super-cooled soda has a mass freezing upon opening, that spreads from the top all the way down to the bottom of the bottle. It’s very exciting to watch the ice crystals spread throughout the soda. I was nervous about the bottles exploding if the soda actually froze, so I didn’t cool them thoroughly enough to get the freezing effect until the last try.

The colligative properties unit was a lot of fun to teach this winter. Adding molality to our repertoire seemed worth the effort to explore the freezing point depression of water and other interesting properties of solutions.