Sharing the topics of measurement and the metric system could at first thought be seen as largely a visual endeavor. Students might measure the lengths of various objects and then convert their results from one metric prefix to another. Ditto mass or volume, with their respective measuring tools. What if the sense of touch could be incorporated to provide a different aspect of learning, beyond simply manipulating the objects?

The authors of Communicating Science Concepts to Individuals with Visual Impairments Using Short Learning Modules (available to JCE subscribers) in the December 2016 issue of the Journal of Chemical Education do just that.

Stender et al. offer four brief modules, including one focusing on the metric system, that are designed for use in an informal setting, although they could easily be incorporated into the classroom. The modules “are designed to educate the general public, including both those who are sighted and those with BLV [blindness or low vision].” All four use either a tactile or auditory learning experience. I was particularly struck by the metric system module, in that it would help students of any visual level to experience the differences between metric prefixes in a new way.

The setup is not difficult to construct and could be saved from year to year. A wooden board one meter long serves as the base (see the article's figure 1 photograph below). The authors’ supporting information document suggests a pine board, but any smooth, inexpensive wood could be used, such as hardboard cut down to size, or even sturdy cardboard. Objects related to the different prefixes—decimeter, centimeter, millimeter, etc.—are attached to the board. “For this purpose, we used one 1 dm rubber disk, an array of 1 cm diameter rubber disks, and cutouts of P20 (ISO scale), 150 (CAMI scale), 1000 (CAMI scale), and 2000 (CAMI scale) grit sandpaper corresponding to 1000, 100, 10, and 1 µm sand particle sizes.” The larger rubber disk is a furniture slider (4 in. / 100 mm) and the smaller disks are surface guard vinyl bumpers (3/8 in. / 10 mm). Since only a small amount is needed of each sandpaper, a local woodworker could be asked if he or she could provide some of the different grits needed.

metric_module_figure_1_ed-2016-00461b_0002.jpeg

Figure 1 - Reprinted with permission from Communicating Science Concepts to Individuals with Visual Impairments Using Short Learning Modules, Stend, Newell, Villarreal, Swearer, Bianco and Ringe. Journal of Chemical Education, 93 (12), 2052-2057. Copyright 2016 American Chemical Society.

When done one-on-one with a facilitator, the module took 5 to 10 minutes. Participants touch the various objects on the board, as well as the length of the board itself, and discuss that each object is smaller by a factor of 10 than the one before it. They also connect the idea of nanotechnology to the objects; “Participants are told that the lower end of the nanoscale includes objects that are another 3 orders of magnitude below the smallest features on the board.” While the activity was described for use with a facilitator, the authors also plan to set up the metric module so that it could be done without a facilitator, by adding Braille labels and explanations.

More from the December 2016 Issue

Mary Saecker’s JCE 93.12 December 2016 Issue Highlights shares more from this month’s issue of the Journal. As always, ChemEd X would love for you to offer your take on any article from this or a past issue of the Journal. All it takes is a short blog post! Start by submitting a contribution form, explaining you’d like to contribute to the Especially JCE column. Questions? Contact us using the ChemEd X contact form.

SaveSave

I have used many silver mirror/Tollen's test labs. I have struggled with some and over the years I have found that this version is very reliable if the directions are followed carefully. Timing is very important too. If you choose to use glassware other than the ornaments, I will tell you that they must be very clean. Sometimes residues from other chemicals will interfere so that the silver does not adhere to the glass. As I said, I have used many versions. I have kept many of them in my paper files and on my computer. I found four different versions in my digital files and of course, none of them have author names on them. I cannot take credit for any of the details, but what I have written is a compilation of many versions. You can find kits available through the usual chemistry education vendors if you wish to go that route. If you are preparing your own silver nitrate solution, you should mix it within a couple of days of the activity. 

Have students work in with one or two partners to create one silver plated ornament at a time. Helping each other is important to complete the ornament quickly quickly. Then the group can go through the steps again until all the students have their own.

Preparing for silver ornament Part 1

Students can follow steps #1-3 at any lab counter. It is important that they keep all solutions labeled so they can keep track of them as they move to the fume hood. 

silver ornament procedure under the hood

Under the fume hood, students will add drops of concentration ammonium hydroxide per directed, add the KOH to the beaker, add more drops of ammonium hydroxide if required and then finally transfer the solution from the beaker into the ornament. Some students may opt to use a funnel for that last transfer.

Plating the ornament with silver

Cover the opening with two pieces of parafilm and firmly press down while gently swirling. Within minutes, you will see a silver coating appear.

preparing for silver ornament #1

Be sure to follow the procedure carefully and you will have a beautiful finished product.

Last month, I shared about a new PD opportunity I had the privilege of participating in called Gizmos. You can read about it here. After Thanksgiving break, my Chemistry 1 and Honors Chemistry 1 classes began our Chemical Reactions unit. In previous semesters, my unit plan looked like the following:

Thanks to Gizmos, I decided to revamp the order of my unit to the following:

My hope was that by altering the flow of the unit, students would benefit tremendously. I was hoping that by pushing the more difficult component of the unit (balancing) to the end, students would not be discouraged. I hoped they would have confidence going into that topic.

Students demonstrated mastery over atom counting (using subscripts and coefficients) and identifying reaction types. Then we jumped into the Gizmos for “Balancing Chemical Equations.” After 2 days, each class took a 5 question formative assessment on the Gizmos website. About 3 questions were balancing related and the other 2 dealt with identifying reaction types. My regular classes saw a 59% and 68.2% average scores, while my Honors classes saw 86.2% and 85% average scores. The lower average in my regular class was troubling; I was sure to include additional practice and resources for those students going into the test and made myself available for help. Unfortunately, many of the students chose not to take advantage of my availability or the provided resources. After I graded the unit tests, I noticed a similar result on the balancing section. Many students did not perform well. So, what does any good teacher do? I went over the test the next week, provided additional practice materials, reviewed the balancing concept, and re-assessed students this week. My hope here was to give students an opportunity to redeem themselves, demonstrate proficiency, and pad their assessment grade category a little bit. I do NOT offer extra credit in class but I wanted to help these students the best way I know how.

Fast forward to the next unit: Physical Properties and Change. I was planning to wrap up this unit within 10 days before our winter break. However, 2 snow days changed those plans. Students will be assessed through current content before break and we will tackle Phase Changes and Phase Diagrams in December, using one of the Gizmo activities available for this topic.

At this point, I do not believe I have sufficient data to determine the success or failure of the Gizmo activity or revamping my Chemical Reactions unit. I’ll try again next semester.

"Mr. T, what's that thing attached to the fourth carbon on this structure?"

"Are there hydrogens there or some other element?"

I routinely get questions like this when I draw structures for my students because I simply don’t have good handwriting. This poor handwriting translates into poorly drawn Lewis Structures. I have had this issue since at least third grade when I earned a C in penmanship from Ms.Dodson. The problem is I get so excited to draw and explain the structures that I tend to draw too fast and have trouble going slow enough to draw good structures. To help with this, I have started using ChemDraw for the iPad.

It's $9.99 in the U.S. iPad App Store, and well worth the money in my opinion. The app has a relatively simple interface that makes drawing structures quite simple. And rather than use a bunch of words here, I would rather show you a couple images and share a video tutorial with you.

First, an image from Notability where I drew some structures, just for context to show why I prefer to use ChemDraw rather than draw by hand.

Hand-Drawn Structures

Next, an image from Notability with some structures from ChemDraw.

Structures from ChemDraw

I also recorded a tutorial to show you how I use ChemDraw to make my structures.

A few final thoughts: If you have an iPad, I would suggest the ChemDraw app as a good purchase if you are teaching much organic chemistry - but even for just "standard" Lewis structures ChemDraw is a great tool to draw relatively clean structures. It certainly has some limitations, but I have found with a bit of practice I can create and manipulate the structures I want to show.

My next goal: Gain enough proficiency that I can use ChemDraw on the spot for teaching, such as mechanisms. I need to become more comfortable with the electron-pushing arrows and such, but I am getting close!

Do you use ChemDraw? Is there a feature you like that I didn't highlight or a technique you would like to share? What other iPad apps do you use that are chemistry-specific?

The American Modeling Teachers Association (AMTA) is an international, professional community comprised of over 2800 passionate, innovative, and connected educators. Members include high school and university level STEM educators, educational research professionals, as well as pre-service and retired teachers.  Individuals join AMTA for a variety of reasons, but perhaps the most valuable benefit is access to the entire repository of curricular materials. Members can download and use (within the guidelines of the acceptable use policy) materials from our physics, chemistry, biology, middle school, and physical science curricula. These include teacher’s notes, lab activities, worksheets, quizzes, and tests. Members have access to the Force Concept Inventory and the Assessment of Basic Chemistry Concepts assessment tools to allow teachers to track student growth. Members will be the first to learn of workshop offerings and distance learning courses.

AMTA recently began a monthly webinar series where expert modelers present on a different topic each month. These interactive, hour-long sessions are only open to current AMTA members. The webinars are recorded and archived and accessible from the members only site. AMTA hosts a member retreat every other year to provide opportunities for modelers from across the country to meet face to face and discuss challenges and best practices. Soon, teachers will be able to search our member database in order to connect with other members in their area.

There are several membership options but the standard fee for a classroom teacher for one year is $60.00. Other options can be found here.  

I recently posted a video on Twitter of an experiment my students were conducting in class. I thought I’d blog about the experiment, since it seemed to generate a lot of interest. In the experiment, solid carbon dioxide (dry ice) is placed in three different liquids at room temperature: glycerol, ethanol, and water. You can watch the video here:

I think the differences observed are fascinating. In each liquid, the dry ice sublimes:

CO₂(s) --> CO₂(g)

The sublimation of dry ice causes bubbles to form within each liquid. However, several differences are observed, depending upon the liquid into which the dry ice is placed. Large, slowly rising bubbles are formed in glycerol, but no fog is produced. In ethanol, a rush of tiny bubbles is produced that move chaotically and rise rapidly. Looking carefully, one notices a thin and wispy fog. When dry ice is placed in water, large, rapidly rising bubbles and a thick cloud are observed.

I recently went into the lab to extend this experiment. I wanted to see what happened when dry ice was added to acetone and hot glycerol (over 150^oC). You can see the results in the video below:

Addition of dry ice to acetone causes a frantic burst of tiny bubbles that almost looks like a tiny explosion!  Also, a very thin cloud is produced. When dry ice is placed in hot glycerol, large bubbles that rise rapidly and a thick, sticky cloud are formed. Table 1 summarizes the results from all 5 liquids:

Table 1: Bubbling behavior and cloud characteristics observed when dry ice is placed in various liquids.

In addition to the observations listed in the table, I also noted that the time it takes for dry ice to sublime varies in each liquid. In the first three liquids (water, glycerol, and hot glycerol), the dry ice took a very long time to completely sublime. In ethanol, the dry ice took a minute or two to fully sublime. In acetone, the dry ice sublimed away in less than a minute!

I’m wondering if it would make a good lesson to have students carry out these experiments and then try to explain differences observed on the basis of the physicochemical properties of each liquid (surface tension, vapor pressure and viscosity). I have tried something similar with my students in laboratory, but not with all five liquids. Also, I have never had students focus on all the parameters (bubble size, character of bubble motion, character of cloud produced, and sublimation time) and liquid properties listed herein. If I try out this experiment, it will certainly be helpful to list the properties of each type of liquid (Table 2). I also think a discussion of the strength of intermolecular forces between molecules in each liquid would be helpful.

Table 2: Properties of liquids at 20^oC (except for hot glycerol) used in this experiment. Properties for hot glycerol at 150^oC.

Perhaps you and your students would like to try out this experiment and come up with your own explanations for what you observe. If this is the case, don’t read on, because below I’ll be sharing how I currently think about the different results based on the properties of each liquid.

Bubble motion: Speed of bubble rise seems to correlate somewhat with viscosity. This makes sense if one considers that viscosity is defined as resistance to flow. This correlation is brought home most emphatically if one compares the slow bubble rise in glycerol (viscosity = 1410 cP) with the explosive bubble flow in acetone (viscosity = 0.32 cP).

Bubble size: Bubble size appears to correlate well with surface tension. Liquids with high surface tension (>50 mN m^-1) tend to form large bubbles while those with low surface tension (~25 mN m^-1) tend to form small bubbles. This difference can be approached semi-quantitatively using the Laplace pressure:

Laplace pressure

Where

pressure difference

is the difference in pressure inside and outside a spherical gas bubble in a liquid,

surface tension

is the surface tension of the liquid and r is the radius of the bubble. If we assume a similar pressure difference in each experiment and rearrange the above equation we find that the bubble radius depends upon the surface tension:

Laplace pressure

Thus, we would expect larger bubbles in liquids with higher surface tension, in agreement with observations.¹

Time for dry ice to sublime: Solid pellets of dry ice take a long time to sublime away when placed in water, glycerol, or hot glycerol. On the other hand, dry ice sublimes away fairly quickly when placed in ethanol. And when placed in acetone, the dry ice sublimes away in less than a minute! How can these differences be explained? When dry ice is placed in water or glycerol, the dry ice undergoes film state sublimation (Figure 1). In this case a single large bubble forms a film around the solid dry ice. This film forms a protective barrier around the solid dry ice that insulates it from the bulk liquid. Because of this insulating barrier the transfer of energy from the bulk liquid to the dry ice occurs slowly, making the dry ice sublime away slowly.

film state sublimation

Figure 1: In film state sublimation, a large bubble forms a protective insulating film around the solid dry ice. There is no direct contact between the liquid molecules and the solid dry ice. The oval in the center represents solid dry ice, the cloud surrounding the oval represents the protective film of CO₂ gas, and the small circles represent liquid molecules.

When dry ice is placed in ethanol or acetone, the dry ice undergoes nucleate state sublimation (Figure 2). During nucleate state sublimation, an enormous number of tiny bubbles form on the surface of the solid dry ice. In this case, no protective insulating barrier is formed. Rather, the dry ice comes into direct contact with the bulk liquid and energy transfer is rapid. Thus, the dry ice sublimes away quickly – in fact VERY quickly in acetone! It is interesting to note that film state sublimation requires large bubbles, so it makes sense that this type of sublimation occurs in liquids with high surface tension. Many small bubbles form in nucleate state sublimation, so it makes sense that this type of sublimation would occur in liquids with low surface tension. 

nucleate state sublimation

Figure 2: During nucleate state sublimation, many tiny bubbles form on the surface of the dry ice. No protective barrier is formed, so liquid molecules may come into direct contact with the solid dry ice. The oval in the center represents solid dry ice, the several clouds surrounding the oval represent CO₂ bubbles, and the small circles represent liquid molecules.

It now makes sense why the dry ice sublimes quickly in acetone and ethanol but slowly in the other liquids. The tiny bubbles observed when dry ice is placed in ethanol and acetone are indicative of nucleate state bubbling. Thus, acetone or ethanol molecules in the bulk liquid can rapidly transfer energy to the solid dry ice through direct contact of molecules, causing speedy dry ice sublimation. The large bubbles formed in glycerol, hot glycerol, and water indicate film state sublimation. In these liquids, the bubbles produced form a film that prevents liquid molecules from directly contacting the solid dry ice. Thus, the transfer of energy from liquid to dry ice is sluggish and the dry ice sublimes slowly.

Cloud production and persistence

A simple way to relate cloud production to vapor pressure is to state that cloud production requires a liquid to have a high enough vapor pressure. This is evidenced by the observation that only hot glycerol does not form a cloud of any sort, while a cloud is formed in all other liquids. However, it appears that if the vapor pressure is too high, a thin and transient cloud results (ethanol and acetone form very thin and transient clouds, while water and hot glycerol form thick and persistent ones). Thus, it appears that in order to achieve a thick, long-lasting cloud, dry ice should be placed in a liquid with a vapor pressure that is neither too high nor too low.   

In order to understand why this is so, it is important to note that any cloud produced in this experiment comes from the liquid into which the dry ice is placed. Thus, when dry ice is placed in acetone, a fog consisting of tiny liquid droplets of condensed acetone is formed. Likewise, dry ice in water forms tiny liquid droplets of condensed water vapor, and dry ice in hot glycerol forms a glycerol fog. You can read more about how this might happen here http://pubs.acs.org/doi/abs/10.1021/ed400754n or here https://www.chemedx.org/blog/dry-ice-water-cloud .

Now we can make sense of the persistence of each fog formed. Tiny droplets of acetone will evaporate quickly because liquids with high surface tension evaporate easily. On the other hand, tiny droplets of glycerol will persist for quite some time, because liquids with low surface tension do not evaporate easily

To summarize: a high enough vapor pressure is required to get a cloud to form in the first place, but once the cloud is formed, its liquid droplets will persist longer if that liquid has a low vapor pressure. Isn’t it fantastic that plain old water at room temperature strikes a perfect balance of surface tension so that clouds are produced upon adding dry ice to it?

If you try this experiment out in your classroom (or on your own) please be sure to let me know in the comments. How did things work out? Did you try any extensions? I also welcome comments and criticisms on my explanations. Where do you think my explanations are on track? Where am I off the mark? Do you have any experiments that might help convince me to change my current thinking?

Happy experimenting!

Acknowledgements: Thanks to to Winthrop Chemistry (@WinthropChem) for alerting me to consider liquid viscosities and intermolecular forces in this experiment.

Notes:

1. If you’d like to take this a bit further, note that the surface tension of water is about 3 times bigger than that of ethanol or acetone. Assuming spherical bubbles, recognizing that r is direction proportional to g, and noting that volume depends upon r³, we would expect bubbles in water to be approximately 9 times bigger than those observed in ethanol or acetone. This seems to fit pretty well with observations. I think a good exercise might be to have students film the bubbles formed in this experiment using slow motion video (most smart phones can do this). Students could then take measurements of the bubbles to quantitatively test the prediction that bubble radius is directly proportional to surface tension.

What are we doing to help kids achieve?

    I am always searching for a good isotope activity that I can use with students.  I want something that is quick, easy, effective and demonstrates the idea of isotopes and weighted average.  I have tried examples using “pre” and “post” 1982 pennies.  The pre 1982 are pennies made of copper.  Post 1982 pennies are zinc with copper coating.  There are activities where pre and post pennies can be analogous to an isotope.  I have also attempted the same idea with peanut and plain chocolate covered candies that model isotopes.  A hazard of that experiment is that the materials are sometimes eaten before the data is taken

    I have finally found a nice little experiment thanks to the chemistry department at Delta College in Michigan.   Here is how the experiment works.  First, I scrounged and found some really cheap plastic Easter eggs.  These represent the “isotopes”.  It is helpful to have eggs that are the same color.  Next, I went to a tractor and feed store and bought a couple hundred of the cheapest nuts that they had in the hardware section.  About half of these I painted black.  Each group of students then received a bag of about 10 “isotopes” (eggs) and were asked to measure the mass of each (the eggs were numbered for accounting purposes).  Students discovered that about six of the isotopes “eggs” were the same mass, two were lighter and two were heavier.  They were asked to put these in groups, to choose one isotope or egg from each group and look inside.  Each of the eggs (isotopes) had the same number of black nuts but different number of the silver or non painted nuts.

    Now here is where the background information started to kick in.  The black nuts were analogous to protons and the silver ones were analogous to neutrons.  Students were even able to take the “average” masses a variety of ways and discovered that the weighted average was most similar to their data.

    This is the first isotope activity I have tried where the students can look inside the model that resembled the atom and find information that reinforced what an isotope actually is.  Furthermore, the quantitative data forced them to examine beliefs about different types of averages and what the numbers really mean.  This took a bit to set up but was inexpensive and can be used year to year.  Give it a try.  Do you have an isotope activity that you like?  Why not share in the comments below….

Obvious answer to my title: Because the College Board (CB) tells me to. Moving on to a more philosophical response...

The first year I taught AP chemistry, I focused on the nuts and bolts of unit design with support from a few friends (“Do I have materials? Quizzes? Labs? Tests?). The second year and beyond, I worked to smooth out nuances, and I'm sure your story is likely similar if you've had the luxury to teach the same course multiple times. Here are a few things that are on my mind now as I reflect on teaching kinetics a few times now. (Quick context: as I shared in my AP Chemistry - Scope and Sequence post, students engage in this unit after stoichiometry, intro to spectroscopy, gases, and reactions units.)

Noticing in year one: I taught my students how to use the method of initial rates. I taught my students rate laws. However, they strugged to differentiate when to use what method. Upon further probing, they struggled to articulate why one might use one method over the other. They could parrot back some ideas ("The rate law tells you about the particles involved in the rate determining step of the reaction."), but I wasn't convinced of mastery and connections. However, I realized this pretty late in the game, mopped up the mess the best I could, and moved on to race through content.

To be honest, until I observed these qualities in my students, I did not realize I suffered from the same short-sightedness. Why is the method of initial rates useful? Why do I teach multiple methods in such a jam-packed course, where from my very limited perspective, the emphasis on the exam, sans maybe ONE multiple choice question, is on application of Integrated Rate Laws? While I’m sure there are many reasons, I realized I wanted my students to take away the notion that different techniques are useful based on the data immediately available, and there are limitations on each method. I made a mental list of considerations for next year (slightly cleaned up for your viewing pleasure):

screen_shot_2017-01-04_at_6.45.55_pm.png

Flash forward one year:My students engaged in the same introductory lab “factors that impact reaction rates”, and then I lectured on the Method of Initial Rates - heavily  based upon Aaron Glimme’s lecture posted online.

What was new-ish: I figured I could then just hammer my students with problems, right? Bummed that my textbook didn’t provide the kind of practice I wanted for my students (too focused on integrated rate laws), I went to the internet. I found a treasure trove of “Advanced Starters for Ten” within the Royal Society of Chemistry’s (RSC) Teaching Resources”, warm ups on a myriad of topics developed by  Dr. Kristy Turner, RSC School Teacher Fellow 2011-2012 at the University of Manchester, and Dr. Catherine Smith, RSC School Teacher Fellow 2011-2012 at the University of Leicester. I gave pages 1 and 3 as a homework set from the Kinetics document. This “10-20 minute” activity served to be pretty challenging for my students (based on the number of kids who sought out help), but it opened up dialogue among my students and I.

Additionally, I engineered a mash-up lab where students practiced the method of initial rates, based upon a lab from Flinn and a lab from Paul Price (here is a link to a video to get the gist). Students had to use the method of initial rates in the formation of a precipitate. I tailored the awesome resources roughly based upon what I felt my students needed - to understand WHERE the initial rate came from, and more practice. (Note 1: Shout out to a student from the previous year’s AP class who optimized the conditions for me - I totally didn’t have time. Note 2: Do you see the pun in the title of this post now?). In my mind, here lay the foundation for my students to be able to articulate pros and cons of the Method of Initial Rates.

20170107_drawing.png

After this lab, my students learned about the Integrated Rate Law, and we had more discussions to continue to flesh out pros and cons of each method after engaging in the "classic" Crystal Violet Lab. (As I write this now, I wonder why I did not give my students an empty version of this table above to fill in throughout the unit???? Note to my future self here, and if you try this, let me know how it goes.)

While no learning sequence is perfect, I am proud of the clearer vision of this progression from Method of Initial Rates to Integrated Rate Law. The previous year  lacked vital practice and thus time for students to create and build a schema. By the end of the unit and even the school year, more students made deeper connections than the previous year. So why do I teach both methods? To help my budding scientists make intelligent choices in the lab, and experience a small slice of that in a controlled fashion. I think that's what CB wants too.

The ever pertinent question - how did this translate to AP results? As I look at the data, I want to tell you it translated to higher scores. To be perfectly candid, for the short answer questions labeled kinetics, the data is about the same- both years between 63% and 73% scored in the highest fourth. Could it have helped in the multiple choice? I’ll never know. One: There were fewer than 5 multiple choice questions on kinetics last year, so no general data. Two: I only received data for 16/20 students from last year - the rest were swallowed up by the CB, never to be found after multiple phone calls to CB and support from my school’s test administrator.

Next time: J. Chem. Ed. Pick- How to improve results from the classic crystal violet integrated rate law lab.

Thanks for reading! What do you notice in your classroom as you teach kinetics? Also, what might you add to my pros/cons table above?

What are we doing to help kids achieve?

     I have a love-hate relationship with people who officially call themselves "Modelers" and who have been trained by the American Modeling Teachers Association (AMTA). Here is the love part: Every teacher I have met who is an official "Modeler" is a pretty incredible person. They are passionate, willing to share, student-centered and love what they do. More importantly as they share their students' work it is clear that the students have advanced conceptual abilities. By "advanced", I mean they seem to be doing much better than my students. They don't just put stuff on paper but explain it extraordinarily well. Mary Palmer is one of those teachers. She has been trained in modeling. She is my "go to" person when I am stuck and trying to figure out a better way to teach something. Her students' journals are nothing short of amazing. I have tried joining the AMTA, examined their curriculum, talked to Mary but something has been missing. I have not yet been able to officially take a workshop. This is the "hate" part. I know it works but I just can't seem to figure it out...something has been missing.

     This week, thanks to Mary, I saw a video by Paul Anderson of Bozeman Science on Modeling called "What is Modeling?". It is one of the best explanations I have ever seen. Let me put it to you this way...stop reading this and watch the video now.  As soon as I saw Mary she said, "That is really it!"

     Here is the "how to" piece in the video that REALLY helped my light bulb go on. Show the kids an event. Have them develop a model. Have each kid draw and write about the model and force them to ask themselves if this model can explain the event. As a teacher, first say something nice about it and then look for their misconceptions and use this as a formative assessment. Combine the individual models with others. Slowly build a larger model and constantly ask if this really explains the event.

     The reasoning that Paul and others suggest this pedagogy is that we use models all the time in science so why not let kids develop them first?  Instead of just putting them into the heads of students, let the students make their own and guide them with experiments. Come to think of it...isn't this what scientists do? Paul mentioned an experiment he had his students model in his video. It just so happened I was on the same topic and decided to try it. The results were far better than if I had just said, "Here...this is the model scientists use for this event..." It was difficult at first but students asked really good questions based on prior information.

      Was this simple the first time? No...it was messy..kind of like eating street tacos. But, like the street tacos, is was a good messy. Students who are not typically confident about science spoke up. It forced some students to think.

     The video and this experience certainly has encouraged me to try this more often. In a perfect world, I would definately take a Modeling workshop. For now, it will be eating lunch twice a week with Mary who has agreed to help me get started. Thinking about going down this path? Don't be afraid. Check out the AMTA now. Have ideas about Modeling...why not leave a comment?

The Gates Foundation has spent over two billion dollars cumulatively and many other organizations and governments also spend millions of dollars each year to fight malaria, the disease that takes more human life than any other.  Suppose that you could wipe out either the mosquitos that are vectors for the Plasmodium parasite that causes malaria or the parasite itself. Would you do so? - or would you hesitate to massively interfere with a worldwide ecology that is not completely understood? The tools that look likely to be capable of exterminating entire species are being developed in laboratories now, especially the technique known as CRISPR, combined with "a gene drive". CRISPR is a revolutionarily powerful and relatively simple chemical technique that makes it possible to edit or delete any sequence in a genome of billions of nucleotides. A "gene drive" is a natural process that tips the scales of natural selection to favor a particular genetic element over the others. The combination of these phenomena could force a man-made genetic modification to proliferate through a population.  For a species that reproduces on short time scale, such as insects or bacteria, such a modification could soon cause a permanent change in the genetics of an entire species. A driven CRISPR modification has the potential to attack malaria at its molecular level, either by modifying mosquitoes or Plasmodium.

Michael Specter builds his description of CRISPR around Kevin Esvelt, whose work in synthetic biology has consistently incorporated an emphasis on the societal implications of the technology. That aspect of his science is reflected in his current affiliation, the Media Lab at MIT, that he joined last year. One of Esvelt's interests is the possibility of a controlled experiment to eliminate Lyme disease on the island of Nantucket. While deer are widely recognized as carriers of Lyme disease, it is believed that the real reservoir is the white-footed mouse population. If the genome of the mouse were modified so as to make it immune to the disease, it is believed that the disease would disappear, without significantly affecting the populations of any mammals. Nantucket Island, off the coast of Massachusetts, would be an intriguing test case for gene-driven population intervention. Lyme disease is a serious problem there, causing people living or vacationing there to take the possibility of infection through the bite of a tick into consideration. Esvelt recognizes that public approval of an experiment in which lab-modified genes are released in the wild would require an extraordinary degree of education about the possible gains and the negative consequences.  Those downsides are not completely knowable in advance, but he worries as much about them as much as he endorses the concept of human-directed biology. Nantucket represents a confluence of favorable factors for a demonstration project. Lyme disease is recognized as a serious problem there; the human population is relatively well-educated (and affluent); the fact that is an island can isolate the test from other areas for control and to limit the extent of unintended consequences, should something go wrong.

This story lies at the intersection of biology and public health, but teachers of chemistry should be prepared to discuss it with students. 

What are we doing to help kids achieve?

    This is about some topics that can sometimes be viewed as nasty four letter words...but maybe they do not have to be. Let’s start with the first topic….curriculum maps. For years I have been involved in a number of schools that at one point or another have said, “Hey, we are going to pull you out of class and in some way, shape or form, have you communicate to us what you are teaching. This will be called a curriculum map.” These people were and still are generally good people who mean well. And from their side of the desk, I get it. An administrator, board member, parent, student or new teacher should have access to what is being taught. It makes complete sense. The hard part is coming up with some meaningful working document. It is kind of like jury duty.  You dread doing it but feel better when it is done. My experience has been pretty bad. Years ago I was told to develop a rough draft of a curriculum map for a course I was teaching. The rough draft would be handed to a secretary who would retype it, make corrections, allow for final approval and then provide it to the school board to be accepted or rejected. I made the rough draft and even included some hand written notes and "post-it" notes about things that I thought might need to be rephrased or changed a bit. I never heard of it again and it did get approved. Years later I saw the final copy. It was the exact same as the rough draft, including scribbled notes in the margin and "post-it" notes. Nobody read it...including the school board. It was thrown in a copier and passed along.

    Next come standards. I live in a state that has standards that many people feel are poorly worded, confusing and are going to be changed soon anyway. You can imagine my enthusiasm when I was told our department had to develop a curriculum map on standards that I did not understand. However...a light appeared at the end of the tunnel…First, an administrator had the courage to say that this would be a living document that everyone knew would change somewhat over time. She wanted a document that everyone in the department could really use, see and have stock in. She gave us the time to work on it.

    Second, she and others picked a program called “Masteryconnect”. This is a program that has an electronic copy of the map for all teachers to see. The entire map is tied to standards that are a version of state, federal and or local standards. Any formative assessment can easily be graded and tied to a standard. The data can be used to break down how the kids are doing in any one standard and plan future lessons accordingly. If we need to change to meet the needs of our students, we can and should immediately. It is not perfect but is trying to maximize data collection and analysis to help teachers and students.

    The ultimate goal of "Masteryconnect" is to have a dynamic document that will allow us to formatively assess the students by the standards and help us to plan and change based on the needs of the students. Although it looks like “teaching by the standards”, grades will certainly not disappear. Instead, everyone will know what those grades mean. Students and teachers should have a good idea before the test how things will go based on the formative assessments. An “A” will mean the student has excelled at mastering the standards. It will not mean that the student had a “B” and brought in a box of tissues for extra credit to get an “A”.

    Here is the real genius of this. As I walked around the room during our inservice I heard more talk than ever before from teachers debating about the strength or weakness of a particular standard, the depth of knowledge of questions in a lab or test or if certain standards might be more important than others and how much time should be spent on each. In the end we did not come up with the perfect curriculum map, timeline or set of standards...but we did embark on a worthwhile fruitful journey. Maybe that is the real goal. Perhaps it is this journey that is far more important than the end product and it is this one that will benefit our students the most. It will be exciting to see where the future takes us….

While we were driving through Tennessee recently, we visited the American Museum of Science and Energy in Oak Ridge, the de facto museum of the ambitious WWII project that separated the uranium and plutonium isotopes used in the atomic bombs dropped on Hiroshima and Nagasaki. I recommend that other scientists and science educators make the effort to visit this historic town and the museum. Of course, the Oak Ridge National Laboratory is still an important research center, involved in applications of nuclear chemistry and computer science, but it evolved from the wartime origins that are described in The Girls of Atomic City by Denise Kiernan. My wife and I both thoroughly enjoyed the book, which describes a time that would be as foreign as North Korea to today’s students in the degree to which workers’ minds were controlled. The story is compelling, and would be unbelievable were it not true. Eighty five thousand Americans were recruited from across the country to work in hastily-constructed factories and a new town, on a project that they was so secret that the workers themselves were not told what they were working on. Most of the workers were women, because so many young men were serving in the armed services. Conditions were primitive and uncomfortable, with snow and cold in the winter and calf-deep mud in the spring and summer. Three different, unproven technologies were being scaled to unprecedented size even as they were being developed. Separate factories were built under wartime urgency to harness the three processes: differential gaseous diffusion, liquid thermal diffusion, and Calutrons (preparative mass spectrometry, for separation rather than analysis). Only a few of the workers had any training in chemistry or physics, and most of them worked at tasks that they were not allowed to not understand. Security was very tight: workers were not allowed to speak or write about their work, even with coworkers from other parts of the plant, and the focus of their work was always referred to as “Tubealloy”. Even the town of Oak Ridge, which had grown to a medium-sized city, did not appear on maps until after the war was over.  These dedicated women were real “Rosie the Riveters”, who helped create America’s war machine while most of the men were fighting overseas. The scientific story of the first atomic weapons has been told elsewhere, but this is the human story – described in the personal lives of six women, whose stories intertwined in a sociological experiment of unprecedented magnitude, ultimately resulting in the surrender of Japan.

Ringing in Volume 94

The January 2017 issue of the Journal of Chemical Education is now available online to subscribers. Topics featured in this issue include: NMR spectroscopy; examining assessment; inquiry-based practices; cost-effective instrumentation; miscibility demonstrations; innovative laboratory experiments; from the archives: lightsticks.

Editorial

To kick off the new volume, Editor-in-Chief Norbert J. Pienta muses on How To Make a Journal Better.

Cover: NMR Spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy plays an integral role in the chemistry curriculum, spanning theory, concepts, and experimentation; it is imperative that the instruction methods for NMR are both efficient and effective. The cover features the laboratory experiment, Rapid Determination of Enantiomeric Excess via NMR Spectroscopy: A Research-Informed Experiment. John S. Fossey, Eric V. Anslyn, William D. G. Brittain, Steven D. Bull, Brette M. Chapin, Cécile S. Le Duff, Tony D. James, Glenn Lees, Stephanie Lim, Jennifer A. C. Lloyd, Charles V. Manville, Daniel T. Payne, and Kimberley A. Roper describe an experiment that exploits chiral supramolecular assemblies for the determination of enantiomeric excess by ¹H NMR spectroscopy.  (This article is available to non-subscribers as part of ACS’s AuthorChoice program.)

Other laboratories that use NMR in this issue include:

Introducing Students to NMR Methods Using Low-Field ¹H NMR Spectroscopy to Determine the Structure and the Identity of Natural Amino Acids ~ Aleksandra Zivkovic, Jan Josef Bandolik, Alexander Jan Skerhut, Christina Coesfeld, Nenad Zivkovic, Miomir Raos, and Holger Stark

Quantitative Analysis of Multicomponent Mixtures of Over-the-Counter Pain Killer Drugs by Low-Field NMR Spectroscopy ~ Aleksandra Zivkovic, Jan Josef Bandolik, Alexander Jan Skerhut, Christina Coesfeld, Momir Prascevic, Ljiljana Zivkovic, and Holger Stark

Using Esters To Introduce Paradigms of Spin–Spin Coupling ~ Kyle T. Smith and Christian S. Hamann

Ideas about using NMR in the high school classroom is discussed in:

Bringing NMR and IR Spectroscopy to High Schools ~ Jessica L. Bonjour, Alisa L. Hass, David W. Pollock, Aaron Huebner, and John A. Frost

Research on how students understand NMR is examined in:

NMR Spectra through the Eyes of a Student: Eye Tracking Applied to NMR Items ~ Joseph J. Topczewski, Anna M. Topczewski, Hui Tang, Lisa K. Kendhammer, and Norbert J. Pienta

Examining Assessement

Analyzing the Role of Science Practices in ACS Exam Items ~ Jessica J. Reed, Alexandra R. Brandriet, Thomas A. Holme; this article is available to non-subscribers as part of ACS’s Editors’ Choice program.

Choice of Study Resources in General Chemistry by Students Who Have Little Time To Study ~ Diane M. Bunce, Regis Komperda, Debra K. Dillner, Shirley Lin, Maria J. Schroeder, and JudithAnn R. Hartman

Inquiry-Based Practices

Characterizing Teaching Assistants’ Knowledge and Beliefs Following Professional Development Activities within an Inquiry-Based General Chemistry Context ~ Lindsay B. Wheeler, Jennifer L. Maeng, and Brooke A. Whitworth

Developing and Supporting Students’ Autonomy To Plan, Perform, and Interpret Inquiry-Based Biochemistry Experiments ~ Thanuci Silva and Eduardo Galembeck

Using Computational Visualizations of the Charge Density To Guide First-Year Chemistry Students through the Chemical Bond ~ Jonathan Miorelli, Allison Caster, and Mark E. Eberhart

Cost-Effective Instrumentation

An Inexpensive Programmable Dual-Syringe Pump for the Chemistry Laboratory ~ Mark S. Cubberley and William A. Hess

Authentic Performance in the Instrumental Analysis Laboratory: Building a Visible Spectrophotometer Prototype ~ Mark V. Wilson and Erin Wilson

Simple and Inexpensive 3D Printed Filter Fluorometer Designs: User-Friendly Instrument Models for Laboratory Learning and Outreach Activities ~ Lon A. Porter, Jr., Cole A. Chapman, and Jacob A. Alaniz

Miscibility Demonstrations

Partially Miscible Water–Triethylamine Solutions and Their Temperature Dependence ~ Johan P. Erikson

For some miscibility video demonstrations available at ChemEdX see:

Chemical Mystery #5: How to burn water ~ Tom Kuntzleman

Like Dissolves Like - Demonstration ~ ChemEdX video collection

Innovative Laboratory Experiments

Magnetic Microorganisms: Using Chemically Functionalized Magnetic Nanoparticles To Observe and Control Paramecia ~ Lynn M. Tarkington, William W. Bryan, Tejas Kolhatkar, Nathanael J. Markle, Elizabeth A. Raska, Michael M. Cubacub, Supparesk Rittikulsittichai, Chien-Hung Li, Yi-Ting Chen, Andrew C. Jamison, and T. Randall Lee

Synthesizing and Characterizing Mesoporous Silica SBA-15: A Hands-On Laboratory Experiment for Undergraduates Using Various Instrumental Techniques ~ Emma M. Björk

Simultaneous Introduction of Redox and Coordination Chemistry Concepts in a Single Laboratory Experiment ~ Philip J. Ferko, Jeffrey R. Withers, Hung Nguyen, Joshua Ema, Tim Ema, Charles Allison, Christian Dornhoefer, Nigam P. Rath, and Stephen M. Holmes

Two-Photon Absorption Spectroscopy on Curcumin in Solution: A State-of-the-Art Physical Chemistry Experiment ~ Julie Donnelly and Florencio E. Hernandez

Improving Student Results in the Crystal Violet Chemical Kinetics Experiment ~ Nathanael Kazmierczak and Douglas A. Vander Griend

From the Archives: Lightsticks

Peroxyoxalate chemiluminescence reactions in lightsticks are perennially popular in JCE. This issue is no exception, where Iain A. Smellie, Joanna K. D Aldred (née Prentis), Benjamin Bower, Amber Cochrane, Laurie Macfarlane, Hollie B. McCarron, Roxana O’Hara, Iain L. J. Patterson, Marie I. Thomson, and Jessica M. Walker discuss Alternative Hydrogen Peroxide Sources for Peroxyoxalate “Glowstick” Chemiluminescence Demonstrations.

Some past JCE laboratories and demonstrations using glowsticks include:

"Cool-Light" Chemiluminescence ~ Bassam Z. Shakhashiri, Lloyd G. Williams, Glen E. Dirreen, and Ann Francis

The Chemistry of Lightsticks: Demonstrations To Illustrate Chemical Processes ~ Thomas Scott Kuntzleman, Kristen Rohrer, and Emeric Schultz

Glowmatography ~ Thomas S. Kuntzleman, Anna E. Comfort, and Bruce W. Baldwin

The Effects of Temperature on Lightsticks ~ JCE Staff

Lightstick Kinetics ~ Catherine L. McCluskey and Charles E. Roser

Lightstick Magic: Determination of the Activation Energy with PSL ~ Thomas H. Bindel

Demonstrating the Antioxidative Capacity of Substances with Lightsticks ~ Robert R. Wieczorek and Katrin Sommer

A Thousand Reasons to Explore JCE

With over 1,000 issues of the Journal of Chemical Education to examine, you will always find something useful—including the articles mentioned above, and many more, in the Journal of Chemical Education. Articles that are edited and published online ahead of print (ASAP—As Soon As Publishable) are also available.

Do you have something to share? Write it up for the Journal! For some advice on becoming an author, read Erica Jacobsen’s Commentary. In addition, numerous author resources are available on JCE’s ACS Web site, including recently updated: Author Guidelines, Document Templates, and Reference Guidelines.

I am not a January resolution maker, but I do appreciate the transition to a new year as a regular marker for reflection on the past, present, and future. Pienta’s editorial in the January 2017 issue of the Journal of Chemical Education serves a similar purpose, as he reflects on its title question: How To Make a Journal Better (article freely available).

What makes up the Journal? At a basic level, content—the articles we see each month. But, as Pienta points out, the pieces that make the published articles possible are many. Authors, partnership with the ACS Publications division, reviewers, and JCE staff, including associate editors and the editor-in-chief. Where can you, the reader, fit in? Consider, are you an author and/or reviewer? What steps could you yourself take to make the Journal better as a resource for other chemistry educators? Consider these excerpts from the editorial.

Be an Author

Reflection:“Creative contributions to the Journal of Chemical Education (JCE) would appear to be a limiting commodity, but our authors never cease to amaze me with keeping the endeavor moving forward…”

Action:“A better Journal means that you, the authors, need to keep up your efforts and to keep the contributions at the cutting edge. Do not forget that new colleagues may need to be mentored about the value of the Journal and getting the next generations to extend that value.”

JCE’s authors continue to come up with novel applications and ideas, as well as updated twists on past material. During my time as JCE’s high school section editor, a main goal was to encourage high school authors to share their work and expertise. I am always pleased to see the fruits of their labor in print. For example, don’t miss Bringing NMR and IR Spectroscopy to High Schools (available to subscribers), particularly for high schools with International Baccalaureate and Advanced Placement chemistry programs, and organic and/or materials chemistry courses. What work can you share through JCE?

Be a Reviewer

Reflection:“Finding appropriate reviewers and asking these volunteers to contribute their time and expertise may be the biggest challenge to running the Journal.”

Action: “If you are not a reviewer, please log in or register an account at the ACS Paragon Plus portal and update your areas of interest/expertise; alternatively, encourage your younger colleagues to use reviewing as a means to find out about cutting-edge research and practice, and to improve their own writing.”

Serving as a reviewer gives a unique behind-the-scenes look at the earlier stages of articles. It is a great opportunity to share your view as a potential reader and user of an article, with the goal of making it an even better article if published. We are all busy, as Pienta states, but reviewers do have the ability to decline an invitation to review a specific article if schedules do not permit. Sign up today!

“How does one make a Journal better? It should be clear that everyone has to contribute.”

Are you?

More from the January 2017 Issue

Mary Saecker’s JCE 94.01 January 2017 Issue Highlights brings together content from this month’s issue of the Journal. Look for further offerings from this month’s authors that are relevant to your own chemical education environment.

How can you make ChemEd X better? Share your take on any article from this or a past issue of the Journal in a short blog post. Start by submitting a contribution form, explaining you would like to contribute to the Especially JCE column. Questions? Contact us using the ChemEd X contact form.

A favorite experiment of mine is the bucket launch. My students and I recently tried two variations on this experiment. Watch the video below and see if you can explain the differences we observed.

Consistently, the one method always worked better than the other. Why do you think this is so?

If you know your chemistry you can figure this out!

HAZARDS:  I describe here some useful tips if you plan on trying this experiment yourself. Please know that all details required for a safe and successful launch have NOT been described herein.  If you try this experiment, you do so at your own risk. The bucket needs to be liberally reinforced with duct tape.  Otherwise, the impact from the explosion will not launch the bucket in the air. Rather, the bucket will shatter into many pieces. After tightly sealing the bottle, STAND BACK.  Pieces of plastic from the exploded 2 L bottle can be thrown as far as 30 m. If the bottle is not sealed properly, hissing noises can be heard as gas escapes from the bottle.  In the event the bottle is not sealed properly, DO NOT approach the assembly until you are certain that all of the gas has escaped.

College Board runs AP Insight, a website full of teaching and assessment tools for teachers and students of AP courses. The site focuses on specific "challenge areas" that tend to give students trouble on the exam. Chemical kinetics is one of the five challenge areas in AP Chemistry. My students and I have been working our way through one of the teaching and learning activities called Concentration vs. Time. The graphical analysis, guided-inquiry questions, and application to past and future content are seriously challenging, and my students report higher levels of understanding than in past semesters.

The "Concentration vs. Time" activity is broken into three tasks: 1) Graphing concentration vs. time data given for three reactions, 2) Analyzing the graphs with guided inquiry to help students understand graphical connections to differential rate laws and then integrated rate laws, 3) Making predictions about a reaction and devising a plan to test the predictions.

Task 1) Graphing concentration vs. time data given for three reactions:  In groups of three, students graph concentration vs. time for a zero, first, and second order unimolecular reaction. The students then work together to devise a list of how the three graphs are similar and different. Finally, the students write statements summarizing what the graphs mean about the relationships between concentration and time.  My students never truly understood the significance of zero order reaction rate being independent of concentration. Some also never understood fully that average rate IS the rate for a zero order reaction while average rate is virtually meaningless for first and second order reactants. They pointed out those important concepts to me this time!

Task 2) Analyzing the graphs: After a short lecture and practice interpreting other graphs and data, the students view a table with zero, first, and second order rate laws and integrated rate laws. The guided-inquiry questions lead them to understand the differences in changes in concentration vs. time in the graph is also displayed mathematically in the rate law.  The integrated rate laws for zero, first, and second order reactions are given in slope-intercept form, which is not how they are displayed on the AP exam's resource page. Students are asked to use their understandings of slope-intercept form and the given integrated rate laws to derive graphs for first and second order reactions. In the past, I taught the integrated equations and showed the graphs simultaneously. The method of asking the students to derive the graph again deepened their understandings. This ability to visualize a graph seems to have helped them in reading and understanding "word problems" as well. I'm not being asked what number matches what variable anymore.

Task 3)  Making predictions:  Students read the description of a reaction and make predictions about the reactions order. They then devise a plan to test the hypothesis. Admittedly, two and a half snow days  cancelled this activity for my students. I will try it out next year.

I guess I'll find out in July if using this activity was the best use of short time! The exam may not have many kinetics questions, but if it does...we're prepared!

See a previous post about using AP Insight.

What are we doing to help kids achieve?

   Some of the biggest misconceptions students hold on to in my course relate to how ionic substances dissolve in water. Thanks to a great experiment developed by Bob Worley it is simple to “probe” a student’s understanding (see“Puddle Chemistry” here) . Starting with a conductivity tester and a few simple ionic solids such as sodium chloride, sodium carbonate and copper(II)sulfate, students do some simple microscale experiments that involve testing the solids separately and together. Students “push” a few crystals in a “puddle” and test the conductivity. The “puddle” conducts. It did not before. They make models to try to describe their experience. I went a step further and incorporated“Atomsmith”(see blog here) so students could look at other models after they attempted to develop their own. Finally, students dropped the sodium carbonate and copper sulfate in opposite sides of the “puddle” and a precipitate formed in the middle. If you are logged in to your ChemEd X account, you can see the activity linked at the bottom of this post. The ultimate goal is that they can develop models and predict the outcome of simple double displacement reactions.

    In theory, this should have worked. In reality, it only worked for some of the students and not all.  After reflecting, here is what I would do differently.

    First, students are dealing with some pretty big conceptual concepts: Dissolving ions, solubility, chemical reactions. My students are 16-18 year old kids that I have in class for 50 minutes a day. I should have introduced these concepts earlier on in smaller chunks and scaffolded them much more. Second, I should have known this if I had taken time to better understand and learn about my students. This is where formative assessment and the standards come in (check out some thoughts here).  Looking over my student's papers, there may have been more misconceptions created because of the way I planned the curriculum. In all of the experiments students can see and observe that not all of the crystals or material dissolves yet the water starts to conduct. In their minds there is evidence that they believe either something DOES dissolve or it does NOT. Clearly, partial dissolving is initially too much to consider.

    So….where to go from here? First, understanding my students, their abilities and teaching accordingly is more important than getting to the last chapter.  People are always more important than test scores. Second, repeated baby steps are not a bad thing...start small and continue to build. Finally, scaffolding...there probably is a way to repeat these concepts in smaller chunks so it is not just a “one and done” activity.  Something tells me that I am not the first to wrestle with this….any thoughts??? If you log in to your free ChemEd X account, you can leave a comment below.

In Chemical Mystery #9, a 5-gallon bucket is launched into the air using the energy released during gas explosions. These explosions result from gas pressure buildup inside a sealed 2 L soda pop bottle. Two slightly different methods of launching the bucket are used, and one works better than the other. Why does one method work better than the other? Check out the original Chemical Mystery #9 post.

As you can see in the video, two different methods of pressure buildup are used. In the first case, a 2 L soda bottle is filled one-third full with liquid nitrogen and sealed. The sealed bottle is then placed in a metal pan of water, and a 5-gallon bucket is placed on top of the assembly. The liquid nitrogen vaporizes inside the bottle and pressure builds until the bottle can no longer hold the contents. The bottle explodes, launching the bucket into the air.  In the second case, the 2 L soda bottle is first filled one-third full with water. Next, several pieces of dry ice (solid carbon dioxide) are placed in the bottle. As before, the bottle is sealed, placed in a metal pan of water, and a 5-gallon bucket is placed on top of the assembly. The dry ice sublimes inside the bottle and pressure builds up until the bottle explodes, launching the bucket into the air.

We routinely observe the bucket to ascend about twice as high when using liquid nitrogen rather than dry ice and water. Why is this so? 

The short answer is that more expansion of gas occurs during the explosion when using liquid nitrogen than when using dry ice in water. For a more detailed answer, read on.

The combined gas law (see equations 2a and 2b, below) can be used to describe the difference in height between the two methods (for a more comprehensive treatment on what occurs during the explosion please see this earlier post).

We’ll begin by assuming that the bucket is launched by gas expansion (the change in volume) as a result of the explosion: 

Equation 1

To find the expansion that occurs in each case, we need to know the volume of the gas just prior to explosion (V_initial) as well as the volume of the gas after the explosion (V_final) for each situation. We can use these values to calculate the change in volume, and the larger this change the higher we would expect the bucket to be launched into the air. 

Since the 2 L soda bottle is filled about one-third full with liquid in each case, V_initial should be approximately equal to the remaining headspace volume of 1.33 L (2/3 of 2L). 

The combined gas law is used to determine V_final in each case:

Equation 2a and 2b

To do this, we need to know the pressure (P_initial) and temperature (T_initial) just prior to explosion. We also need to know the pressure (P_final) and temperature (T_final) of the gas after the explosion. 

It takes about 10 atmospheres of pressure to cause a plastic 2L soda bottle to fail. Thus, we can use 10 atm as Pinitial in each case. We also know that after the explosion, the gas will take on the temperature and pressure of the ambient air. Thus, we can use Pfinal = 1 atm and Tfinal = 273 K (we conducted the experiment on a cold day in January). 

So far, all parameters are identical. The difference between each method becomes apparent when we consider the gas temperature just prior to explosion. In the case of liquid nitrogen, the Tinitial = 105 K.¹ In the case of dry ice in water, the temperature is around 273 K.²

Using these values in the combined gas law, we find:

Equations 3

Substituting the results from Equations 3a and 3b into Equation 1, we find a change in volume of 33.3 L for the liquid nitrogen method and 12.0 L using dry ice in water. Thus, we would expect the liquid nitrogen to expand 2.8 times more than the carbon dioxide under the conditions used. This is in fair agreement with the observation that the bucket tended to go twice as high using liquid nitrogen rather than dry ice and water.

Thus, the greater expansion in the nitrogen over the dry ice in water method stems from the fact that the nitrogen enclosed in the bottle is much cooler prior to explosion than the dry ice in water. This cooler temperature allows for greater expansion upon explosion, which results in a bucket that is launched higher. 

HAZARDS:  I describe here some useful tips if you plan on trying this experiment yourself. Please know that all details required for a safe and successful launch have NOT been described herein.  If you try this experiment, you do so at your own risk. The bucket needs to be liberally reinforced with duct tape.  Otherwise, the impact from the explosion will not launch the bucket in the air. Rather, the bucket will shatter into many pieces. After tightly sealing the bottle, STAND BACK.  Pieces of plastic from the exploded 2 L bottle can be thrown as far as 30 m. If the bottle is not sealed properly, hissing noises can be heard as gas escapes from the bottle.  In the event the bottle is not sealed properly, DO NOT approach the assembly until you are certain that all of the gas has escaped. Do not attempt to try this experiment by placing dry ice alone (with no water) into the 2L soda bottle. We have observed the bottle to take a VERY long time (up to an hour) to explode when placing only dry ice (with no water) in the bottle.

NOTES

1.    Nitrogen boils at 105 K at a pressure of 10 atm. See https://www.bnl.gov/magnets/staff/gupta/cryogenic-data-handbook/Section6...

2.    In the second case, a binary CO₂-H₂O system is enclosed in the bottle. A phase diagram for this binary system shows that CO₂(g)/CO₂(s)/H₂O(l)/H₂O(s) exists at 10 atm and roughly 273 K (see J. Chem. Educ. 1994, 71, 903 – 904.)

Register now to attend the AACT webinar on January 25 at 7:00 EST. This webinar will introduce demonstrations you can use when they first learn the material, or as they prepare for the AP test. You'll be provided with demonstration questions that can be scaled up or down depending on the level of chemistry that you teach.

Hosted by Jamie Flint.

Free Webinar for all AMTA members!

The NGSS calls for the use of the engineering design process in science classrooms K12. Let’s discuss what this means for the modeling classroom. Bring your ideas about how and when to integrate the engineering design process and engineering projects into your classroom.  

This session will be hosted by Kathy Malone and Anita Schuchardt.