Monday, October 2, 2017

What students need to understand gases at the particle level

Student #1 - The gas particles expanded because there was empty space.
Student #2 - Gases like to fill their container.
Student #3 - The balloon filled up because there was a vacuum.

There is a common misconception or lack of conception about gas particle motion.  The ideas start when students are very young as we teach them about solids, liquids and gases very early.  To compensate for the fact that students are not ready for the particulate level at this age we use observations of what happens at the macroscopic level.  Liquids take the shape of the container but do not fill it.  Gases fill the container and take its shape.  Solids are unaffected by their container.  Even though we do not express the particle level (or do so very poorly) students will still formulate ideas about why these differences exist.  By the time students finally get to a chemistry class where they can connect the macroscopic and particulate levels there are significant obstructions in place.  
There are a number of demonstrations available to test these obstructions and misconceptions and get students thinking.  But teachers must be very wary of oversimplifying the demonstration and offering their own explanations.  This can cause students to reinforce their misconceptions.  Instead focus on observations and begin providing students with the tools to organize particle level pressure analysis based on speed/temperature, direction, number of particles, size of the container and surroundings.  For an example consider the demonstration where a balloon is blown up backwards using a flask with hot water.  
Initially the flask has mostly air in it at a similar pressure to the surrounding atmosphere.  As the flask is heated, steam pushes some of the air out leaving the flask to contain steam and some hot air.  There is a smaller density of particles in the flask than out because the higher speed creates a similar pressure with fewer particles.  If there were the same density of particles in the flask as outside then the higher speed would result in a greater pressure in the flask than the atmosphere.  A greater pressure would mean more frequent collisions with the the container, and also the hole which would lead to more particles leaving the flask than entering.  It is only when the particle density is smaller in the flask that the pressure will be the same.  
Now the balloon gets placed on the flask and the flask is removed from the hot plate.  The particles in the flask begin to slow down as the temperature drops.  This causes fewer collisions and smaller collisions and thus a drop in pressure occurs.  The external or atmospheric pressure is constant and thus becomes larger in pressure and the balloon is pushed in until the smaller volume in the flask reaches a similar pressure to the atmosphere again.  
In order for the student to properly analyze such a situation they really need to articulate multiple steps and critically analyze the number of particles, volume of container, speed of particles and how each of these affects the overall pressure.  This task can be aided by using particle level drawings but it is indeed a formidable task.  Most students being overwhelmed with this task resort to adding in human features to the particles instead.  The particles have less space so the air particles move in to fill the empty space.  An underlying feature of these student alternative conceptions is that particles will move towards an empty space but students do not realize why this occurs.  This is crucial to eradicating some of the structures that we begin with. To begin addressing this have students draw a simple diagram with multiple colors and motion in multiple directions such as in Figure 1 below.

Figure 1:  Student representation of an initial state of a gas.  

Then instruct the students to determine where the particles will be a short time later (IE after the time needed to move the length of each arrow).  Have them draw four different diagrams in sequence showing the particles’ positions based on their motion.

Figure 2:  Student works showing how the particles move about based on their initial positions and motions

Ask the students why the particles moved the way that they did.  Ask clarifying questions if needed such as should the particles change speeds, will the particles collide with the walls and other particles?  Try and emphasize that there is no special direction or cause of the motion but that the particles were just moving to begin with and thus changed where they were.
Now the plot twist.

Have the students restart on a new whiteboard if possible and draw a bunch of particles in one location such as in Figure 3 below.  

Figure 3:  Students restart having all particles in 1 location (IE in a balloon)

Now have them complete the same process as before.  They should note that as the particles move about that the particles spread throughout the container because the motions are in different directions and there is nothing to oppose their motions.  

Figure 4:  Gas particles starting in a confined space that become free to move around

Why did the gas particles fill the container?  Was it because they like to spread out?  Was there a big reason or did they just happen to be moving in a way where they would spread out for no reason other than they were already moving to do so?  The particles that stay in the corner bump and collide causing them to change directions while those moving away from the corner are not impeded.  There is no force needed for the particles to fill the container, there is no suction.  The gas fills the container solely because gas particles move and they are moving in various directions.  (AP Chemistry teachers might even have seen a professor express that it is equally likely that all particles could have all of the energy as an equally likely microstate as a somewhat even dispersal.  This is false because the initial conditions make it impossible for that to occur.)

Figure 5:  Teacher representation of gas particles moving and a confined gas that was released moving.  The bottom image is a confined gas for comparison purposes.

In Figure 5 above one can see the difference between gas particles moving throughout an enclosed space and gas particles confined to one small section of a confined space.  Did the left corner exhibit “suction” towards the particles?  Did they move towards the empty space because they wanted to fill it?  Absolutely not.  Rather the fact that gas particles move in various directions as an intrinsic quality of the particles is all that is needed for the spread of particles to occur.  There is no differentiation between the top series and the bottom series in Figure 5.  There is no way for the empty space in the second series box 1 to pull or force the particles to move.  There is no such thing as a suction force.  A gas particle cannot be pulled.  But there is an interesting tendency for the gas to spread based on the particles various motions.  
A high-level discussion that may be appropriate is what happens when you breathe.  It is probably natural for most people to assume that when they take a deep breath in, that they pull air in.  If you breathe in right now it will appear to you that you are controlling the air.  But you are not.  Your lungs cannot exert a force on air outside of your body.  Only the particles touching your lungs can be affected by your lungs.  The air that moves in when you breathe in was already on its way towards your lungs, you just caused fewer particles to be restricting their motion in.  By expanding your lungs using your muscles, fewer particles leave your mouth and the same amount of air is still moving towards your mouth and lungs as before.  Thus a net flux of air in occurs.  But those particles weren’t sucked in, or pulled into your lungs.  
(This discussion might also bring up the misconception that air leaving a rocket causes the rocket to move forward, a common misconception from Newton’s 3rd law)
After discussing breathing I had students ask about slurping noodles and drinking out of a straw.  Both were fantastic additions to the discussion as slurping requires contact between the substance and this makes it possible to create a force on the noodle particles.  The straw of course is dependent on the external pressure.  Some follow up concepts worth using to assess are why do gases move from high pressure to low pressure and modifying that with varying temperatures.  For example, if a high temperature gas and low temperature gas have the same pressure, why is there not a net transfer of particles?  Would the densities of the gases be different?  What would happen if  the hot gas cooled down?  Do the collisions cause speeds to change?  Do all gas molecules in a sample move at the same speed?  
With a better understanding of why a gas will fill its container and a better model to work with students should now be ready to give a much better analysis of common gas law demonstrations.  If anyone does the 2-L with a nail in it or the notecard on a mason jar filled with water; both of these demonstrations rely on a small amount of water leaking.  This causes the trapped gas inside of the container to decrease in pressure because the space available increases from the small amount of water leaving.  This causes the pressure from the atmosphere to be greater by enough to balance the pressure of the weight of the water and trapped gas.  For the 2-L the water stays in as long as the cap remains on and for the notecard the notecard stays in place and prevents a student from being soaked.  
If you use a vacuum pump to show marshmallow, balloon or shaving cream expansion make sure to explain to the students how the vacuum pump is engineered to allow particles to leave the glass dome and get pushed out by the engine, but particles are prevented from re-entering the dome.  Vacuum filtration is always a much more visible representation of this that students that continue on to organic chemistry in college will likely see repeatedly.  
When I first did gas pressure demonstrations the goals were simple.  I wanted students to articulate that gas pressure was caused by collisions and that pressure could be exerted in multiple directions.  But now I want them to be able to get to the point where they do higher levels of analysis of what is happening during demonstrations.  I want them to organize when temperature changes and when it doesn’t.  I want them to identify when there is a difference in particle densities.  I also want them to avoid adding human qualities to gas particles and this exploration where students draw arrows and then follow them through like a comic book strip might just be the key to seeing that to fruition.  


Figure 6: More student creations

Friday, September 29, 2017

Teach Students the Positive Impacts of GMOs

Scientists often have difficulty communicating their research to the public and false marketing has filled that gap for some time with regards to nutrition and food production.  Meaningless and deceptive labeling have been used and misconceptions have developed.  Social media has exacerbated the disconnect between public perception and reality with regards to nutrition and food production and there are consequences to this distortion.  This gap exists for many well intentioned people and teachers might be the key to bridging the gap.   Public opinion has begun to reverse this trend in topics such as climate change and vaccines but agriculture and food lag behind.  It would surprise many to find that there is greater agreement on the safety of genetic modification of food than there is on climate change.  Many would assume that this ignorance is of minor consequence.  They would be wrong.  As the world population has increased and poverty levels diminish farmers have quietly gone about their business.  Most are unaware that over the past twenty years farming has had very little increase in farming acreage despite farmers feeding many more people due to population growth and reduction in starvation.  
The benefits of using genetic modification with regards to food are diverse and impactful.  The environmental impacts alone are huge and include a reduction in carbon dioxide emissions, less pesticide use, safer pesticides5 and the potential for reductions in animal cruelty6.  Genetic modification has the potential to allow those allergic to peanuts to eat peanuts safely, those with Celiacs disease to eat bread and vegetarians to eat the Impossible Burger © that cooks and tastes like meat due to genetically engineered yeast that produces hemoglobin.  The healthiness of produce that is organic, genetically modified or non-GMO are similar but typically most healthy for the genetically modified versions.  Foods with non-GMO labels often lack vitamins in order to meet the criteria for labeling.  Organic food and traditional agriculture are similar in health benefits but for many the price of organic food would cause the consumer to purchase fewer fruits and vegetables that are one of the most critical components of a healthy diet.  
Scientific evidence can be drowned out by loud voices.  Posting or sharing an article with an exaggerated headline is much more common than one that is scientifically sound.  Many people have heard false information for so long that they are unwilling to believe evidence and will dismiss experts as shills.  These people still influence the supply of food distributors and producers by being organized and frequent communication.  But it is time for the evidence and truth to trump fear-mongering.  Teachers are in a key position to do this.  We have an audience and we are tasked with educating that audience about using evidence, critical thinking and evaluating sources.  Science teachers of all fields can find connections to the environmental impact and potential for genetic modification.  Teach your students about the different methods of genetic modification and point out the absurdity of transgenics being singled out in spite of no evidence of safety differentiation between other genetic modification methods.8    Teach your students about the historical methods of food production and some of the amazing things we do today that improve our lives.  Teach them that the non-GMO movement was one of deception and marketing and that scientific evidence continues to struggle against fear of consumers.  Play an NPR interview with farmers and have them write about whether farmers should cave to financial pressure or do what is best for the planet.  If you want to have a discussion on capitalism and economics make sure to discuss the organic industry and its lobbying efforts along with their deceptive marketing to make money off of the vulnerable (or that purchasing non-GMO leads to an increase in slavery).  Even if you do not teach science you can still make a large impact on your students and your community.  

Resources for science teachers that I have found helpful:
9.  Video about GMOs for students
10.  Food Evolution narrated by Neil DeGrasse Tyson

Twitter accounts to follow

Please add suggestions for good resources in the comments below too.


Sunday, September 10, 2017

Book Recommendations for Chemistry Instructors

It can be easy as a teacher to slip into a routine where your focus is solely on student learning.  But as teachers it is important that we value education and learning and a great way to do this is by reading about our fields.  Here is a variety of chemistry and chemistry-related books that I have enjoyed many of which I now use annually in my teaching.  

The best book for chemistry teachers to read is a textbook about physics.  There is yet to be a chemistry version of this, but the author (Arons) spent considerable effort to interview students at various levels about their physics understandings.  One of the key ideas from this book is that students can produce correct answers without understanding what they are saying and this book explores what questions to ask to get to the point where understanding can actually be assessed.  For a chemistry teacher there are topics that might not directly impact their teaching, but energy, force, measurement and many other topics will influence your understanding of the topics and allow you to question at a particle level what is happening in chemistry in a way that you were not able to before reading the book.  The approach to assessment is valuable in all science courses and this book frequently impacts my teaching of chemistry.  This book is quite expensive, so try and find it through a colleague or library first.  It is worth tracking down.

#2 The Periodic Table - Eric Scerri
Eric Scerri has a lot of wonderful books and is able to get into a lot of material that chemistry teachers will often hand wave over.  Here is a blog post about 3d and 4s orbital ordering.  In this book he discusses the first periodic tables developed and what traits each scientist included and omitted.  He talks at length about Dmitri Mendeleev and compares what he did with what others had done before him as well as what others did better than him.  This book also includes some chemistry content about the periodic table that is masterfully presented.  The book’s subtitle “Its Story and its Significance” is also appropriate as the book builds an appreciation for the wealth of experiment that resulted in the modern periodic table.  Chemistry teachers often celebrate the mole, but the periodic table is a much more important accomplishment.  

#3 The Poisoner’s Handbook - Deborah Blum
The title of this book caught my eye and the book far exceeded my expectations.  Deborah Blum works through a series of different poisons all through the lens of the founding of respectable forensic science during the prohibition era in New York City.  This book discusses poisons, antidotes, detection, history and politics along with some captivating stories.  This is a much lighter read than the first two books but also might contribute many interesting anecdotes to your teaching.  

#4 Napoleon’s Buttons - Penny Lecouter and Jay Burreson
Napoleon’s Buttons suggests 17 chemicals that could be considered to be the most influential in world history.  The book goes through some chemistry and some history and it absolutely loaded with interesting information about both.  The connections between the two are also really well developed and this was an enjoyable and educational read.  

#5 Great Physicists - William H. Cropper
This is a book that is a series of biographies about famous physicists.  The best part of this book to me is that it gives a fantastic rundown of the development of thermodynamics that includes the key experiments and the confusion that resulted from them.  The book balances the personal stories of the scientists with their key experiments and also some basic theory about the physics they did.  Your lectures about entropy and Gibbs free energy will be better after reading this book.  

#6 Chemistry in your Kitchen - Matthew Hartings
A chemist that loves to experiment with cooking and is well versed in the chemistry we know and do not know about with regards to cooking.  This book was very interesting, a lighter read and also might inspire you to cook something.  The book is very well written in that it will connect chemistry and other science concepts with cooking, give some potential recipe alterations but it allows you to put together your own alterations rather than just providing too much direction.  I very much enjoyed this book and I will be seeking out more reading about the topic.  This book has 15 chapters that each detail a specific food or drink, some personal connections and some science behind the cooking variations possible.  

Andy Brunning makes infographics for chemicals that you typically are not aware of but have experienced nonetheless.  He is great to follow on twitter and this book is a collection of his most interesting chemistry graphics organized by themes such as poisons, colour and lots of food information.  If you are a chemistry teacher I highly recommend you purchase a poster for your room from his collection.  

#8 Uncle Tungsten - Oliver Sacks
This is the story of Oliver Sacks as a  young child who has a surprisingly large access to chemicals.  Oliver describes his curiosity as a child, how his family and friends supported this curiosity and a variety of experiments and experiences that shaped his knowledge of chemistry.  There were a few experiments that were new to me that I ended up trying from this book and the perspective is a good one to experience as a chemistry teacher.  

#9 A Tale of 7 Elements - Eric Scerri
Prior to Moseley’s experiments determining atomic charge, there were many quibbles over element discovery.  After his development of the answer key for the periodic table so to speak there were 7 elements missing between hydrogen and uranium.  This book describes the search and discovery of these 7 elements.  The philosophy of how credit should be awarded is discussed with some interesting plots such as an element that was discovered and then later a more stable isotope was found.  And Tc was discovered frequently before it was actually discovered.  Eric Scerri was the one author to appear on this list twice and he has written several other great books that I have enjoyed reading besides these two.  

#10 Transforming Matter - Trevor H. Levere
Starting with alchemy this book moves through the history of chemistry particularly focusing on the early scientists and their struggles to make conclusions from experiments when there was not a lot of knowledge to build on.  A lot of good information about Antoine Lavoisier, Jacob Berzelius and a wide variety of scientists that were familiar and many that I was not aware of.  This book had a lot of interesting stories about the politics and drama behind the scenes of the famous experiments with plenty of chemistry mixed in.  

#11 Elements - Theodore Gray
This book is now a series of books (Molecules, Reactions, The Element Vault) that pair good photographs along with chemicals.  I have used these books to start class off by reading to my students about a particular element or compound and there are many interesting facts presented about them along with a quality picture to go with that information.  The Element Vault also comes with a thin sheet of gold foil (and a couple other fun things) if you happen to teach Rutherford’s gold foil experiment.

#12 Plutonium - Jeremy Bernstein
This book caught my eye at a bookstore and I enjoyed it very much.  The book discussed the discovery of plutonium in the context of world war II.  It combines the historical perspective with the challenge of being able to separate elements with such similar electronic structures from each other when elements only differ based on electrons two energy levels beneath the valence shell.  

#13 Chemical History of the Candle - Michael Faraday
There is a horrible tendency in chemical education to avoid understanding what a flame is.  A flame combines chemical reactions with light and to really comprehend at the particle level what happens in a flame is often diminished by vocabulary in place of visualization.  This book is unique in that it discusses a brief history of the lectures at the Royal Society and then works through the demonstrations done by Michael Faraday to show how a candle works.  The chemical demonstrations are brilliant given the time they were executed and could be replicated in the classroom with a bit of glassware preparation.  The lecture is really a great example of phenomena based teaching or utilizing evidence in the classroom.  

Currently reading
The Chemistry Book - Derek B Lowe - This book is a similar to the Elements series by Theodore Gray but from a historical lens.  It moves through major milestones in chemistry by assigning each a date as best as possible.  On one page is a picture of the chemicals or scientists or apparatus and on the other are a couple of paragraphs describing the event and its significance.  

I lucked into this book while in a used book store.  It was written in the 1950s and is a really interesting perspective as it discusses the challenges that accompanied scientific discoveries (before cars, before paid lab positions, before science supplies could be purchased).  I have not yet reached the gold foil experiment, but Rutherford really accomplished a lot prior to that experiment that might often be overshadowed by one of the most important experiments in science.  

In queue
The Secrets of Alchemy - Lawrence M. Principe