Field of Science

Shedding some light on chemistry: Mole Day and the Year of Light

[If you want to participate in some science about science blogs, see the bottom of this post!]

It's October and there is lots of science to celebrate.  Chemists in the US and elsewhere are celebrating Mole Day on Friday (October 23 at 6:02 pm) to honor Avogadro's number (6.02 x 1023 items are in a mole -- it's the chemist's version of a dozen).  It's also the International Year of Light, and while you might think that light is the purview of physicists, it's an element of chemistry as well.  I suggested in a recent essay that one might want to celebrate the year of light on the 10th October at 3 in the afternoon (3 x 1010  is the speed of light in cm/sec)

I've written two pieces on the relationship between chemistry and light for the celebration.  The first for Nature Chemistry, The Enlightenment of Chemistry, looks at the two-way relationship between chemistry and light.  Light is  not just an energy source for doing chemistry, but the production of light in various ways has pushed chemistry forward.  The full text is here.

The second, for the UN's Year of Light blog celebrates the October 27th anniversary of Bunsen's and Kirchhoff's publication on the spectroscope and atomic emission spectra — and the role the spectroscope played in not only filling out the periodic table, but in confirming the periodicity of the table.
"Hunting for new elements spectroscopically meant you didn’t actually need to have any of it in your lab or even on your planet, as long as you could observe the light from a burning sample. In 1868 several chemists and astronomers independently observed a faint line in the spectrum of the sun, and assigned it to a new element, helium, which as far as they knew did not exist on earth. It would take nearly 30 years for two Swedish chemists to confirm that it was present on earth — by matching the spectrum with that of a gas found in a uranium ore. (The helium to be found on earth comes from radioactive decay.)" — read the rest here.
Want to participate in some science to celebrate?

Help us do science! I’ve teamed up with researcher Paige Brown Jarreau to create a survey of the Culture of Chemistry's readers. By participating, you’ll be helping me improve the blog and contributing to SCIENCE on blog readership. You will also get science art from Paige's Photography for participating, as well as a chance to win a t-shirt, a $50 Amazon gift card and other perks!   It should only take 10-15 minutes to complete. You can find the survey here:

Building scientists #istandwithahmed #kierawilmot

So what's this kid doing in the high school auditorium after school?  He's drilled holes and put pipes into a cooler, there's some kind of heating device or trigger. Wires.  And it looks like a boat load of some sort of chemical in that bowl that he's dumping in there.  And then...and it shoots out some kind of gas.  Kids scream. The gas begins to cover the stage.

"What's happening?" wants to know the teacher who hears the commotion from the hallway.  "I'm testing a fog machine I built for the class play."

Yes, at first glance the situation looks potentially perilous.  But a quick question, followed by a bit of common sense and the teacher is reassured that all is well.

Now that everyone is sure that there is no bomb, what should happen to the kid?

A.  Pull the child into the principal's office and demand that he sign a statement admitting his guilt.

B.  Call the police, who will arrest him and charge him with building an explosive device.

C. Call the police, who will arrest him and charge him with building a "hoax bomb"

D. Nominate him for a theater award for special effects, for having designed and built an inexpensive fog machine to use for the school's upcoming production of Grease.

The kid is my kid and the school's response was D.  But imagine if my kid wasn't white and male.  If his name were Ahmed Mohamed or Kiera Wilmot?  There might have been handcuffs, felony charges, letters home to parents about "the incident".  If someone had called the police, would they have arrested him because he couldn't explain why he'd built one, when they could have rented a fog machine?  (The police thought it suspicious when Ahmed Mohamed couldn't tell them anything more than his device was a clock.) Why would you build a fog machine, or a clock?  He must have built it for a purpose, nefarious almost certainly.

Perhaps the purpose was to understand how these machines work?  There is an amazing amount of joy in showing that you understand something well enough to build a working apparatus. To tweak and fix.

As a parent, I want the school to exercise an abundance of caution.  But once you're sure it's just a clock — or a fog machine — perhaps it's time to slow down, and engage some common sense.  Is there anything else that suggests this kid would build anything danger?  Besides his name, or the color of her skin, or his religion.

Scientists and engineers are not hatched full grown from eggs in labs.  As kids, they tinker and think and build and design, with Legos and parts from Radio Shack and Home Depot.  They are in theater and on robotics and Science Olympiad teams.  We need to get as excited about what they do as we are about how the football team is doing.

From the portals of hell to built-in fire protection: intumescents

A friend posted the link to this demonstration, wondering if it was safe. (Do listen to the children in the background - their cries of "kraken" at 1:02 are worth it.  Science is great fun!)

The caption that came with it noted that it was a mixture of ammonium dichromate ((NH4)2Cr2O)and HgSCN (mercurous thiocyanate).1 Mercury and chromium, probably not something you want to eat I told my friend. The whole thing made me curious, just what were those tentacles come out of the burning pile? And what chemical reactions were driving it?

It's a coupled set of decomposition reactions. The volcano comes from the decomposition of ammonium dichromate

(NH4)2Cr2O7(s) → Cr2O3(s)+ N2(g)+ 4H2O(g)

The reaction produces a lot of heat, which makes the particles being thrown off by the rapid expansion of the two gases (nitrogen and water vapor) glow.

The heat then triggers the decomposition of the mercury compound:

2 Hg(SCN)2(s) → 2HgS + 4CS2 + carbon nitrides

The erupting tentacles are an example of intumescence2, a property of mercury thiocyanates noted long ago by the venerable Friedrich Wöhler3. It's a well known demonstration, often called Pharaoh's Serpents. Many material intumesce when heated, and thus produce their own insulation.  Some passive fire protection systems rely on this property of polymers, by which they essentially rapidly produce their own insulating layer upon heating, or by swelling up to block air ducts to prevent smoke and other gases from spreading too quickly through a ventilation system.

It works with mercuric thiocynate as well (Hg(SCN)2) — by some accounts even better — and better yet if you toss a bit of potassium nitrate and a bit of fuel in the form of sugars. In other bits of historical trivia, the mercuric thiocyanate was originally made by the aptly named Otto Hermes. The sale of mercuric Pharaoh's Eggs ceased after some kids ate them with deleterious (fatal) effects.

If you just want to see the snakes minus chromium salts or mercury - try this demonstration based on calcium gluconate instead or check out pyrotechnic expert Tenney Davis suggestions in the Journal of Chemical Education.

1.  From the Latin verb "to swell" — related to thumb and tuber (as in root vegetables like potatoes)

2.  The chemist who showed in 1828 that compounds made by nature do not have some "vital essence" that distinguishes them from the same structure crafted by a chemist from inorganic (never living) materials.  Something the Food Babe and hawkers of 'bioidentical' hormones do not get.

Read more:

Brian Clegg at Chemistry World.  A paper on the demonstration from Journal of Chemical Education in 1940, by Tenney Davis of MIT who taught courses in explosives way back when ($).

A chemistry decoder

A basic guide to decoding organic compound names
© Andy Brunning/Compound Interest
The August 17th edition of C&EN — Chemical and Engineering News, the American Chemical Society's weekly newsmagazine — was devoted to the intersection of chemistry and the internet.  I have a piece in there on the ways in which the internet allows pseudoscience to spread and what chemists might do to counteract the spread.  I point to Andrew Noymer's work on the mathematical modeling of rumor spread, which suggests that rumors and autocatalytic reactions such as the classic Lotke-Volterra systems are not dissimilar.

Noymer's results suggest that damping down the spread of rumor requires both persistent debunking and increased resistance among the susceptible population.  Though at first glance it seems counterintuitive, just periodically debunking rumors leads to a steady state situation, where there is always a (not so small) part of the population who believe.  Debunking needs to be strong and regular, and even then, if you don't have a resistant population, you land in a steady state regime.  The best you can do is to reduce a rumor to something that periodically breaks out.  Like the "Mars will be as big as the Moon in the sky!" meme which you see circulating on social media every summer like clockwork.  (Spoiler alert: It wasn't. It won't be.  Ever.)

What does it take to make a population resistant to pseudoscience?  Some tactics are not unique to the pseudoscience issue:  teaching critical thinking (as Phil Plait points out and Joel Achenbach implies here). Slower fingers when it comes to hitting "share." But it also means giving the population some basic tools for reading science.  After the Royal Society of Chemistry released a large study of the public awareness of chemistry, I wrote that it might be helpful if instead of periodic tables, chemists handed out a cheat sheet for decoding chemical names.  I wished and voilà, the brilliant Andy Brunning of Compound Interest created this graphic.  Print it out and post it in your kitchen.  Link to it on Facebook.  Browse the rest of his collection.  Buy his forthcoming collection about the chemistry of food and give it to the family member who keeps sending you links to the Food Babe.

Most all, talk about what you do as chemist, debunk garbage science when you hear it, swiftly and without mocking, and grab as many opportunities as you can to help people learn to decode chemistry on their own.

Eating periodically: is there thallium in your wasabi?

Wasabi, Iwasaki Kanen 1828
via Wikimedia Commons 

Could your wasabi peas be poisoning you?  Short answer. Maybe.

Delish recently posted an article on thallium — a highly toxic metal — in kale, the quintessential healthy green.  The Internet relished the irony of finding toxic metals in the highly touted greens. The piece points to an article in Craftsmanship magazine, which attempts to make a link between consumption of kale and thallium levels.  This is not new news.  There are dozens of reports, going back two decades, in the scientific literature of thallium in cruciferous vegetables, such as kale and brussell sprouts — and wasabi.

Thallium is definitely a nasty element, and has an infamous history of use as a poison in fact and fiction, starting with Ngaio Marsh's Final Curtain.  Read Deborah Blum's hair-raisingly fascinating Poisoner's Handbook (or her short article at Wired about a recent murder case in Princeton).  But as with everything, dose makes the poison, and the amounts of thallium in plants vary widely depending on the concentrations in the soil.  In highly contaminated soils, plants can contain enough thallium to be hazardous.  But if such highly contaminated soils were widespread, we'd have seen the effects already. (See this paper for some background.) (Also, you can leverage this ability and use it to clear out the thallium from a contaminated area.)

So how does thallium get into the plants? There is some evidence that thallium ions travel the same pathways as potassium ions (which play key roles in plant metabolism), and so might find their way into plants (and animals) though similar processes.

Thallium is also in the same column as boron, and elements in the same column of the periodic table often have similar behaviors, because their electrons are arranged in similar patterns.  For example, strontium, which is underneath calcium, sneaks into the body by way of the same processes calcium does. Boron is found in plants (coffee is a good source, and plants in the same family as kale are also heavy absorbers of boron); it is believed to be critical to cell wall formation.

And if there is boron and thallium, indium - in the same column is another likely companion. And yes, indium has been detected in plants in the cabbage family.  

As always, eating a wide variety of things is good advice, and it's key to remember that "natural" is not the same as "safe."

First woman in 'space'

I keep checking to see how far away New Horizons is from Pluto (459,770 km at 0235 GMT) even though I know there's nothing to see at the moment, but I am a space junkie.

The first space launch I can remember seeing is the last of the Mercury missions, launched in May of 1963.  I was 5 and I was hooked on space.  In retrospect, I suspect my hours watching rockets erect on their launch pads, the vapor streaming off the only sign this was live TV,  fed my desire to do science as much as the biography of Marie Curie I chewed through while ill one summer or my parents' careers.

I'd be glued to the TV for every launch I could for the next decade, and I confess I can still be found streaming a launch in the corner of my screen while grading.  I'm still hooked on space.

S o I was delighted to discover the first woman to leave the atmosphere — at least the breathable part of it — was both a chemist and an alum of the college where I teach.  In October of 1934, Jeannette Ridlon Piccard, a licensed balloon pilot, flew a balloon with her husband on board to an altitude of 17.5 km, well into the stratosphere.  Her altitude record (for women) would not be broken until Russian astronaut Valentina Tereshkova's flight in June 1963.  You can watch the Piccards take off in this video and see the wreckage of the gondola after they crash landed.  Her first person account of the trip was published in the New York Times the next day, including her chagrin at such an inelegant landing.

Ridlon's entry in Bryn Mawr's Undergraduate Catalog of 1916, she
would concentrate on chemistry and physics over the next 2 years. 
Piccard was a Bryn Mawr College graduate, class of 1918, taking course work in chemistry and physics, as well as psychology and philosophy.  She went on to get her master's degree in chemistry from the University of Chicago and later a Ph.D. in education from the University of Minnesota.  All wonderful preparation for being an...executive secretary (those were not the days), pilot and stratospheric explorer.  Piccard's papers are the Library of Congress and I'd love to go read the experimental notes from that epic flight.

Piccard's grand-nephew Bertrand Piccard is one of the pilots on the Solar Impulse, a solar powered plane attempting to circumnavigate the globe.

My thanks to Bryn Mawr College's registrar, Kirsten O'Beirne, for figuring out how "majors" worked in the early 20th century.

Sequencing data

The New York Times recently posted a piece on problem solving which asked readers to first solve a problem:

"We’ve chosen a rule that some sequences of three numbers obey — and some do not. Your job is to guess what the rule is. We’ll start by telling you that the sequence 2, 4, 8 obeys the rule."

You can test your hypotheses by typing sequences into three boxes to see if they follow the unstated rule.  Once you think you know, you type in a description.  Most people it turns out, suggest an answer without ever trying a sequence that returns a firm "NO."  Psychologists interpret this as being evidence of confirmation bias: once we get a "yes" for our theory - we don't poke around trying to find a "no."

When I teach chemical kinetics, I point out to students that few experiments can prove a reaction goes in a particular sequence, only that the data is consistent with a proposed mechanism.  No answers can be as or more critical to problem solving as yes.

I failed to 'correctly' solve the puzzle, [SPOILER ALERT] though I did get several no answers.  One rule I tried was an: 21, 22, 23 = 2, 4, 8.  The sequence 1, 1, 1 follows that rule (11, 12, 13 are all one), but yielded a no.  The rule an = 2 x an-1: 2, 2x2=4, 2x4 worked for every sequence I tried, but is not 'the 'answer.  The answer is that correct sequences have each number larger than the last.

The study suggests I failed not only because of confirmation bias, but because I complicated the problem, assuming that there was some sort of trick to the rule. Actually, I assumed the technical mathematical meaning of sequence held, in that there was a rule that uniquely specified each number in the sequence given the starting value(s). An ordered list of numbers, each of which is larger than the previous value is not a sequence in the mathematical sense.

In retrospect, I should have tried the sequence 0, 0, 0. It follows the rule I proposed (an = 2 x an-1) as the correct one, but returns a "no." It would have ruled out my proposed rule, a useful "no".  (I might also have tried non-integer numbers.)  I failed in part because I didn't understand the question they were asking, we didn't have the same definition of "sequence."  In some sense I fell prey to the "when all you have is a hammer, everything looks like a nail" scheme.

There are more than 2500 rules that would give you the mathematical sequence 2, 4, 8.  See Sloane's encyclopedia of integer sequences.  My first proposed sequence is A000079 in the collection.

For more about sequences and Sloane's encyclopedia, read this article at AT&T.

Eating periodically (not a quantum diet)

What elements are in chocolate?

Answer #1

Carbon (Chocolate)
Hydrogen (CHocolate)
Oxygen (ChOcolate)
Holmium (CHocolate)
Cobalt (ChoColate)
Lanthanum (ChocoLate)
Astatine (Chocol(ChocolAte)
Tellurium (ChocolaTe)

So you could have: CHoCoLaTe or CHOCOLate or....

Answer #2

(Presuming the letters are not required to be used in order - and yes, I wrote a piece of code to give me this for any word)
All of the above and
aluminum (Al), chlorine (Cl), calcium (Ca), cerium (Ce), helium (He), actinium (Ac), Technetium (Tc), thorium (Th), thallium (Tl) and tantalum (Ta)

Answer #3

Elements that have been detected in chocolate (in this case dark chocolate, rough percent of my recommended dietary allowance in parentheses assuming I eat only a 100 gram bar).

Carbon, hydrogen, nitrogen, oxygen, potassium (why cocoa is detectably radioactive), calcium (about 5% of my RDA), iron (125%), magnesium (70%), phosphorous, potassium (almost a gram, 20%), sodium, zinc (40%), nickel, sulfur, silicon, cadmium, lead (yep, lead, mostly from dust contamination during transport), mercury, arsenic, uranium (trace amounts, but yes, more radioactivity), aluminum, copper (from pesticides, but on the plus side gives you your RDA for this element), and manganese

Nearly one fifth of the known elements have been detected in chocolate, which clearly should be the backbone of any periodic diet.

What other elements are you eating?

Just in case your chocolate doesn't have enough radioactivity for you:

Chemists are wildly polysemous

STO-3G//STO-3G calculated Raman spectrum of arsole
A few months ago this BBC news report - about the evacuation of a building because of a volatile compound got chemists on Twitter talking about language, particularly those words that mean one thing to chemists and something quite different to the rest of the world.  (Thanks @NatalieFey_NLS, ‏@stephengdavey and @stuartcantrill!) Like volatile (high vapor pressure vs. explosive) or to my mind the most overexposed chemical example and the inspiration for far too many t-shirts: mole.  One thing led to another, or at least, one comment by @stuartcantrill led to my Thesis column in  this month's Nature Chemistry.
Is RT retweet or 2.5 kJ/mol?

This piece was pure fun to write.  I enjoyed crowdsourcing examples of chemical double meanings. (List of 200 examples is here.) By far the favorite mechanism of formation for chemists is polysemy, where words share a common ancestor, but the meanings have drifted apart.  Take flush, as in flush a column, or flush a toilet or  flush game or even a straight flush.  All these senses derive from the Latin fluxus for flow.  (Don't see the connection to poker? The OED suggests you think of a flush as a "run" or flow of cards.)

Sometimes the two meanings sit close to the surface for chemists, other times we are pretty blind to the lexical ambiguity.  My youngest son is toying with the idea of a chemistry major, and when I read him examples from the list, he was quick to note both senses for many words: cell, salt, aromatic.  But when I got to molar, he wanted to know what else it meant beyond the concentration of a solution.  "Teeth?" I suggested.  He face palmed.  Whether he majors in chemistry or not, we've already messed with his mind.

Polysemy is productive — as the linguists would say — not just in terms of the language, but of new chemistry.  We ought not to discourage lexical play in chemists (not that one has much control over language in any case, IUPAC's gold book notwithstanding) it gives us a rich set of images to draw on and as I said in the essay, "we can't look for what our language doesn't let us imagine."

Read the essay here. ($)

What is the half-life of a tweet?

My tweets apparently have a half-life of about two hours, but I have no idea if that's unique to me.  My spouse is new to Twitter and as I was showing him how he could see some data about his tweets, I noticed that the graph of the data looked familiar.  Probably because I taught chemical kinetics twice last year (in pchem and general chemistry).

Over lunch today, while waiting for my car to be serviced, I decided to explore the kinetics of my tweets.  I used data from the first 10 hours after I posted a tweet, and used tweets that had several hundred total impressions and few retweets.  Using five data sets from the past month, I fit the tweets to linear models for 0th, 1st and 2nd order kinetics.  R2 values suggest that a 1st order model is most appropriate, with a rate constant of 0.35/hour, which translates to a half-life of 2.0 ± 0.4 hours.  I'm curious if that's relatively constant for me, or whether it's characteristic of other parameters, but time is up.

Perhaps because I'm writing this outside in a park, I'm reminded of an infamous problem about the temperature dependence of the chirp rate of male snowy tree crickets in many general and physical chemistry texts.  A discussion of the phenomenon (first recorded in the late 19th century, and not true of cricket everywhere) can be found in Thomas Walker and Nancy Collins. “New World Thermometer Crickets: The Oecanthus Rileyi Species Group and a New Species from North America.” Journal of Orthoptera Research 19 (2010): 371–376.