The vast majority of molecules you will ever see here don’t contain a metal ion. And so it goes for many chemists - myriad possibilities exist with just carbon, hydrogen, nitrogen, and oxygen - add in sulfur and the halogens and you have lifetimes of work for armies upon armies of chemists. The chemistry of metal compounds merits its own subfield, inorganic chemistry, which encompasses essentially the rest of the periodic table (plus the aforementioned atoms).

The number of possible molecules, as you can imagine, goes up sharply as you start putting other atoms in there, so many inorganic compounds are only known to inorganic chemists and those who work routinely with them. There are a few inorganic all-stars that every chemist will recognize, though. In synthesis, Grignard reagents are amazing compounds that are generated by the addition of magnesium (metal - you actually use bits of metal!) to alkyl halides. These are workhorses in organic chemistry, as are Grubbs’ Catalysts, a series of ruthenium complexes which won Grubbs the 2005 Nobel.

In biochemistry (and laundry science - more on that in a minute), the inorganic-complex forming hero is EDTA, or ethylenediaminetetraacetic acid: Read the rest of this entry »

Hydrogen peroxide seems boring at first blush- after all, you can get it in those little brown bottles at the drugstore, and they don’t do much but fizz - and then, only when

you pour it on a cut (more on that later). H₂O₂ has a structure a lot like water - H-O-O-H instead of H-O-H. That O-O bond is the peroxide bond, and it’s what’s responsible for H₂O₂’s oxidizing power.

The drugstore H₂O₂, you’ve probably noticed, is only a 3% solution (and it can still burn your skin a little bit). Even in a lab, the highest concentration I can easily get is 30%. These bottles are vented, since peroxide tends to decompose to water plus oxygen. This is the bubbling reaction you obersrve when you pour it on a cut. This is due to the action of the enzyme catalase, which exists to do just this. Like many enzymes, catalase is present at an unusually high concentration in liver. Chop some liver up finely and pour some peroxide on it (3% from the store will do) and you’ll see what I mean. Certain other metal compounds will work, notably silver and manganese dioxide.

The 30% peroxide we get in the lab comes with dire warnings not to spill it on paper or anything combustible (because it would ostensibly start a fire). I believe it, but it’s never happened to me. Peroxide actually gets dangerous in the 70%+ range. It will happily propel a rocket. It’s really amazing how a 25-fold or so increase in concentration can make something act like a completely different substance.

Inspired by yesterday’s entry, which wasn’t really a molecule proper, today’s entry is about the diamminesilver (I) complex, better known as Tollens’ Reagent. In practice, this is usually generated by taking a solution of silver (I) nitrate and adding a drop of NaOH solution. This generates some Ag₂O, or silver (I) oxide. Addition of aqueous ammonia will dissolve the silver oxide, generating the diamminesilver (I) complex. Why do we care? Read the rest of this entry »

As we’ve discussed, gold is among the so-called “noble metals,” named as such for their lack of reactivity. Gold won’t dissolve in concentrated solutions of nitric acid or hydrochloric acid. Both are strong acids, and nitric acid is a potent oxidizer, which tends to help quite a bit in dissolving metals. It turns out chloride and an oxidizer are the necessary and sufficient conditions to dissolve gold.

Enter aqua regia, which is just a mixture of the two acids (providing both the chloride plus the oxidizer). Typically you use ~25% concentrated nitric acid and ~75% concentrated hydrochloric acid, but other proportions are known (the other one I see some people use is 75/25, which I think is quite a bit nastier.

Like so many colorfully named classics, aqua regia derives its name from alchemy. As you have no doubt figured out, it is from the Latin for “royal water,” from its gold-eating superpowers. It was discovered in 800 AD by the alchemist Abu Musa Jabir ibn Hayyan.

One unique thing about aqua regia is that it decays after being mixed up, so you always have to make it fresh. The nitric acid slowly works on the chloride ion, generating chlorine gas, leading to a pleasant swimming-pool aroma if you just catch a whiff, or choking fumes if you get more than that (Chlorine is really a violent poison in much higher concentrations than you run into at the pool, and it has been used as a war gas).

Also generated is the toxic nitrosyl chloride (NOCl), which is a beautiful reddish-orange. So you mix concentrated nitric acid (colorless, or maybe tinted just barely yellow, but mostly clear), concentrated hydrochloric acid (colorless), and you get a red-orange, bubbling, smelly solution that can dissolve gold. Can you imagine what the alchemists must have thought of this?

My very favorite story about aqua regia is this: during World War II, a Hungarian chemist living in Denmark, George de Hevesy, dissolved two fellow scientists’ Nobel Prizes in aqua regia literally as the Nazis stormed into Copenhagen so they wouldn’t be stolen (he assumed, correctly, that the Nazis would just leave the chemicals alone). After the war, he recovered the gold, and the Nobel committee recoined the prizes. You can read more about it here.

See you tomorrow.

The noble metals seem to have the most interesting chemistry. Silver (I) nitrate, or AgNO₃, is a soluble compound. Its crystals are boring, whitish, maybe violet or gray if they’re a bit old, but only just. Its solution in water is clear. If you spill the dilute solution on yourself, it doesn’t sting at all (in fact, many hospitals still use silver nitrate eyedrops on babies, in case mom is harboring an STD that might make its way in through the newborn’s vulnerable eyes). Nothing too interesting happens until you go out into the sun. Then, photoinduced electron transfer from silver to, well, whatever’s lying around happens. It stains skin and clothes pretty readily. The silver (I) ion is reduced to silver (0), or silver metal. Interestingly, it looks boring and black, not silvery. Nitric acid will remove it, albeit at the risk of losing the use of your hands and/or pants. Better to try sodium thiosulfate.

Read the rest of this entry »

Lead is one of the most familiar heavy metals to people. Disquieting is the fact that so many people haven’t handled it because of all the concern about its toxicity. Fishing weights are increasingly being replaced with heavy but less-toxic alternatives, like bismuth.

If you’ve never handled lead, please try it. I worry that it will go the way of mercury and you just won’t be able to get it in ten years. I can get all sorts of weird stuff in a chemistry building, but you don’t really have that luxury. It is soft and magic. If you have it in bar form you can bend it like Superman. It will make your week. Just wash your hands afterwards, and don’t store it in the butter dish.
Enter one of my heroes, Theodore Gray, with his Periodic Table Table. His entry on lead does the element more justice than I will. He also notes a few places you can get lead: hardware stores, fishing stores, and Wal-Mart. With lead’s wide use in plumbing, it probably won’t go away as quickly as I claim (the symbol for lead, Pb, comes from the latin plumbum. as you might expect, this is where the word plumbing comes from).

Lead is a lot like mercury - toxic, but not so terrible. You can handle lead pretty freely - for instance, I’d hold lead in my hands, not mercury. You can dent it with your fingernail. It’s surprisngly heavy, but not as heavy as gold or tungsten. Like mercury, the soluble compounds are much worse. One is Lead (II) acetate:

Read the rest of this entry »

This is the yellow pigment in turmeric, the spice responsible for curries being nuclear holocaust yellow.

Read the rest of this entry »

So, as we mentioned yesterday, good old Thomas Midgley had made quite a mess of things with his organolead snafu. By way of apology, he gave us CFCs. Why would we want them?

To make a refrigerator, you need a gas that can go pretty easily between liquid and gas - so, something with a near-room temperature boiling point at atmospheric pressure. If you’re a chemist, you’re thinking: ether, anhydrous ammonia, sulfur dioxide, and a bunch of other nasties. That was, in fact, the stuff we used first (Well, not ether. But loads of SO2 and NH3). Trouble was, it was so toxic it kept killing people. We needed something that balanced volatility with low toxicity.

Read the rest of this entry »

Tetraethyllead is another one of those organometallic compounds that is absolutely bizzare unless you work with them yourselves. It’s got lead in it - in fact, it’s over 60% lead by weight, but it’s a clear, lipophilic liquid. It has the effect of decreasing the tendency for gas to combust prematurely in an engine, or “knock.” That is, when added to gasoline, it increases its octane rating. This is all an octane rating is - a measure of a fuel’s propensity to prevent knock. 87 is more likely to knock in a high-compression engine than 91.

Here is the structure of tetraethyl lead:

Read the rest of this entry »

A lot of people have heard of “noble gases” - this is that rightmost column of the periodic table: Helium, Neon, Argon, Krypton, and Xenon. They exist pretty much on their own; it is very hard to make a compound out of them, and when you manage to, they’re fleeting sorts of things, waiting to react with whatever’s around.

Another series of noble compounds exists; the noble metals. These are named “noble” for the same reason - their relative lack of reactivity (the idea being that there are “noble” metals that hold onto their electrons in a dignified fashion, and “base” metals that deign to react with the other peasant molecules). Because of their lack of reactivity, they occur as the “native” metal much more often than the base metals (which occur as ores).

All that aside, when you want a metal that won’t react, you’re pretty good with platinum. Platinum is also very high-melting, so the development of a crucible made of platinum was a help, since various things could be heated in it without reacting with their vessel. These are curious objects. If you have any platinum jewelry, you know it really doesn’t wear. Unless it’s polished, though (and Pt crucibles usually are just brushed), it just looks like stainless steel. It doesn’t look like as expensive or special as it is until you pick it up - then you realize it’s denser than gold, and nearly twice as dense as lead - and maybe you are holding something a little bizzare.

Read the rest of this entry »