I am an astrobiologist, sci-fi geek, and professor of everything groovy. I write about science, culture, math, history, space, and science fiction. Perhaps like you, I'm seeking a greater understanding of the nature of life and asking myself why all of this really matters. Come with me, and we'll ask some questions together.
Sulfur is one the coolest chemical elements. It's crucial for life as we know it, has more solid allotropes than any other element, produces a lot of the scents that we recognize with our sense of smell, was one of the few elements in pure form that was known by ancient people (it's even mentioned in The Odyssey), it's yellow in its natural form but melts into a beautiful red and burns blue, and it's become part of the highlight of my graduate research (okay, that last bit probably only makes it super important to me). I recently discovered two rare allotropes of the mineral form of elemental sulfur (also, technically called polymorphs) at Borup Fiord Pass, a glacier system in the High Arctic. One of those allotropes, known as beta-cyclooctasulfur (ya, cool name), usually only forms in warm environments and wasn't expected to be found on an Arctic glacier. I'm working on some videos to share information about my work with sulfur and Borup Fiord Pass. However, in the meantime, here's a fun video from FuseSchool that explains some of the awesome chemical properties of sulfur. Check it out:
Professor C. Bodin was LEGO's first female scientist, released back in 2013. It's awesome to see gender inclusivity with toys for children (and some of us who are really just older children), especially with LEGOs, which were one of my primary influences for creativity as a kid. Professor C. Bodin came equipped with two Erlenmeyer flasks, one containing something blue and one containing something yellow. The only thing I'm left wondering with her character is what those two different substances might be and what kinds of ideas children might have for what happens when Bodin mixes some of the blue stuff with some of the yellow stuff.
Alberta, Canada, has some of the world's largest pyramids. But these weren't megastructures built by ancient peoples for the honor of their leaders, to connect the afterlives of pharaohs with the gods, or to provide a special place of worship for their people. These pyramids are made entirely of yellow elemental sulfur!
Sulfur is currently being harvested in large quantities due to its recovery from tar sand oil and gas in operations in the northwestern U.S. and western Canada. Once the sulfur is removed, the oil and gas companies can try to sell it, but sulfur is down in the markets right now and that means a lot of sulfur is just being stored, in a process called "blocking", where large blocks of elemental sulfur are produced and then stored.
Blocks of sulfur, 25 feet tall (credit: Gord McKenna)
One place where blocking has gone rampant is near the tar sands of Alberta, Canada. As of 2012, oil and gas extraction of sulfur in this region accounted for roughly 1.5 million tons per year of sulfur. At that time, 600,000 tons were being blocked each year. That led one company, called Syncrude, to start building The Great Sulfur Pyramids of Alberta!
These giant pyramids of sulfur blocks can be easily seen in satellite images. Andrew David Thaler, writing in Southern Fried Science, calculated from images and data that the largest of the sulfur pyramids was at 2,840,000 cubic meters in volume back in 2012 (it's continued to grow since then). In comparison, the Great Pyramid of Giza is only 2,580,000 cubic meters in volume. With the current rate of growth of the Great Sulfur Pyramids of Alberta, they're on track to become the largest human-made structures ever (by volume). Here's a comparison of bases of the Great Pyramid and the largest of the sulfur pyramids:
Those are some huge pyramids! I think I'll have to throw a visit to these pyramids on my travel list. Just to see those large, yellow structures of sulfur would be intriguing, even if their presence is due to the fact that we're now pushing the limits on extraction of hydrocarbons from the Earth.
Sulfur burning at Kawah Ijen (image: Oliver Grunewald)
Sulfur is most certainly one of the coolest elements. Sulfur was one of the few elements that ancient people knew of (back in a time when it was known as "brimstone", and before people even knew what elements actually are). Sulfur is the 10th most abundant element in the universe and the 6th most abundant element on Earth by weight (although most of it is in the core, along with lots of iron and nickel). Sulfur causes our flatulence to smell bad and allows people to perm their hair (due to the disulfide bonds that are broken are reformed between the amino acids in the hair). Sulfur also presents itself in some awesome colors when it's in its elemental form. For instance, here's a picture of solid elemental sulfur at room temperature from my book shelf:
Elemental sulfur is a beautiful yellow color in its natural solid form. However, when it melts, it turns various beautiful red colors:
Red molten sulfur at Kawah Ijen volcano (iamge: Photovolcanica)
Yellows and reds are cool, but elemental sulfur also burns in a beautiful blue color. Here's a video from scientificpages on Youtube which shows powdered elemental sulfur burning in open air:
In the video you can see the sulfur turning red as it melts, but you can also see the blue flame forming over it. Burning sulfur is something that anyone can try at home, but finding large amounts of elemental sulfur melting and burning in nature will only happen in a few places. One of the best known places where this occurs is in Kawah Ijen volcano, in East Java, Indonesia, where the elemental sulfur extruding from the volcano is harvested by a local company (the image at the top of this post is from Kawah Ijen). Some of the best pictures of the sulfur in Kawah Ijen have been taken by Oliver Grunewald. Here's one of Grunewald's photos of the sulfur being harvested at night:
It's truly a beautiful location for seeing elemental sulfur in all of its various colors.
Update Note, 30 January 2024: I used to have an image from the film Indiana Jones and the Raiders of the Lost Ark at the top of this article. It showed the face melting scene at the end of the film. However, Google constantly sent me violation reports because of this rather famous image, so I removed it. That said, enjoy what follows for the strongest known acid.
The strongest known acids on the planet are something called superacids. These are acids that are more acidic than a pure solution of sulfuric acid! That's most definitely "face melting acidity". Even the word "superacid" sounds like something you don't want to dance with on a Saturday night. There are many superacids that chemists have formed, but by far the worst of the worst (the most hated and cursed? well, no, it's just the strongest) is the superacid known as fluoroantimonic acid. Fluoroantimonic acid can be estimated to be over 10 quadrillion times stronger than sulfuric acid! (see the discussion below on the Hammett acidity function to see how I got that number) Fluoroantimonic acid has the chemical formula H2FSbF6 which shows you that it's composed of bonded atoms of fluorine (F) and antimony (Sb) with some hydrogen (H) as well. Let's chat a tad about the chemistry of fluoroantimonic acid and why you most definitely don't want it on your skin (or anywhere near you, for that matter, unless you're a chemist who's working with the stuff).
Dropping Acid
From left-to-right: strong acid, dilute acid, base (image from SeattlePI)
Acid (which comes from the Latin word(s) acidus/acēre, which means "sour") is something that people have known about for a long time. Acids are literally what you are tasting when you taste something sour (hence the name). Lemons and other citrous fruits have a sour taste due to citric acid. We use microbial lactic acid fermentation (producing lactic acid from glucose) to make sauerkraut, sour beers, and kimchi (and, incidentally, lactic acid fermentation ruined a pot of stew I had sitting out last week). You may have noticed that your vomit has a sour taste. That's because of the acid in your stomach that normally helps you to digest your food, though the burning sensation you feel in your throat from vomit has more to do with your stomach enzymes which cleave amino acid bonds to break down proteins (update: I had hydrochloric acid listed as the main stomach acid that causes the acrid taste of vomit, but a reader clarified that the real nasty smell and flavor comes from butyric acid).
There's a lot more to acids than taste. Put simply, an acid is a substance which can donate a proton. In chemistry, we tend to think of these proton donations as shuffling of hydrogen nuclei (a hydrogen atom, which has one proton and one electron, is only a single proton when it's ionized). There are lots of molecules that can donate a proton to water (to form the hydronium ion) or to another molecule (something that accepts a proton is called a base). Some molecules are much better at doing this than others. The molecules that are the best at donating protons are called strong acids. Strong acids include things like hydrochloric acid (HCl), nitric acid (HNO3), and sulfuric acid (H2SO4). In these cases, the chloride (Cl-), nitrate (NO3-), and sulfate (SO42-) ions are very stable as ions in solution, which is why they're so good at giving away those protons. For instance, in the picture below, the behavior of hydrochloric acid in water is compared to that of acetic acid (HC2H3O2):
As the picture illustrates, hydrochloric acid donates all of its hydrogen (protons) to water, while acetic acid tends to mostly remain as acetic acid and only a small amount dissociates to form hydronium ions and acetate ions. Because of this, we consider hydrochloric acid to be a strong acid and acetic acid to be a weak acid.
Superacids
When considering the acidity of a substance, many acids are compared in their acidity to that of sulfuric acid. The sulfate ion is very stable in its ionic form in solution and so it's not a happy camper when bound to a proton or two (which is a state called "protonated"). Like I mentioned earlier, a superacid is one that is considered to be more acidic than 100% sulfuric acid. When you have that strong of an acid, a measure of something like pH (the negative log of the concentration of protons in solution) is no longer adequate. Instead, chemists can turn to something called the Hammett acidity function.
I won't explain the Hammett acidity function here, but it can loosely be thought of as what the pH of a solution would be if it were possible to pack trillions of trillions of hydronium ions into a solution. A pure solution of sulfuric acid would have a Hammett acidity function value of -12 (so, kind of like having a pH of -12, if that were possible).
This is Magic Acid, the second most acidic superacid. It's Hammett acidity function is -19.2!
What About Fluoroantimonic Acid?
Fluoroantimonic acid, the strongest known acid, has a Hammett acidity function value of -28! (though there are also sources out there stating an unconfirmed value of -31.3) This is what the pH of a solution would be if it were possible to pack 1028 moles of hydronium into each liter of solution. To give you an idea of how crazy that is, a solution with a pH of 1 (which is easily acidic enough to burn your skin) has 0.1 moles of hydronium per liter. Since the molar mass (the mass per mole) of hydronium is 19.02 g/mol, a quick calculation will show that fluoroantimonic acid is as acidic as a solution would be if it contained over 1026 kg/L of hydronium. That's more than the known density of neutron stars! (Luckily, that's not really how these superacids work.) As I mentioned above, it can be estimated that fluorantimonic acid is about 10 quadrillion times stronger than sulfuric acid. Since sulfuric acid has a Hammett function of -12 and fluorantimonic acid has a Hammett function of -28, the difference is 16, or about 1016 more moles of hydronium. That's 10 quadrillion times more! However, as I mentioned above, this isn't really how superacids work and the Hammett function can only loosely be idealized as the negative log of the acid concentration.
This is the structure of fluoroantimonic acid. White balls are hydrogen, green - fluorine, and purple - antimony.
Fluoroantimonic acid is a ridiculously strong acid. It will eat through glass and plastic. It will react explosively with water (so it is only mixed in solution of hydrofluoric acid). It can protonate almost any organic molecule (force a proton onto the molecule), and it will most definitely cause some massive trauma to any living organism (by massive trauma, I mean it will certainly destroy any and all flesh it comes into contact with). There's really only one way to store it. A bond between fluorine and carbon is the strongest chemical bond in organic chemistry. Polytetrafluoroethylene (PTFE), brand name known as Teflon, is composed of repeating units of carbon bonded to fluorine atoms. For a container to hold fluoroantimonic acid, it has to be made out of PTFE. Yup, you read that right: the strongest acid known to humanity can be stored in the same stuff that keeps your eggs from sticking to the pan when you make breakfast.
PTFE - Keeps your breakfast from sticking to the pan and kicks the snot out of the world's strongest acid
I bet you'll never look at your non-stick frying pans the same way again! There are some uses of superacids like fluoroantimonic acid. These acids are great at creating substances known as carbocations (molecules with ionized carbon atoms) and providing environments for studying such substances. Carbocations are intermediates in some economically important reactions, so studying their behavior when isolated is pretty important. Outside of the need to protonate things that normally aren't protonated or to create these carbocations, it's pretty safe to say that there's absolutely no need to have superacids like fluoroantimonic acid around. Well, maybe not. Here's a TEDxGhent talk from a couple years ago by Lennart Joos where he suggests using a superacid known as phosphotungstic acid to combat smog:
So maybe there are some great uses for superacids. Still, I don't think I have any need to play with something like fluoroantimonic acid during this lifetime. My hats off to those chemists who deal with this stuff safely and securely (and my hopes that it remains that way in their future work). The science behind fluorantimonic acid is awesome, but when I think of the stuff all I can imagine is all of my skin melting off in the most painful of ways. Scary.
