Growing up, I believed there was real magic in the world. I'm not talking about believing in ghosts, ghouls, sorcery, or secret words that unlocked doors; I knew magic was real because acids were real. In my imagination, they could eat through anything. When other kids transformed the living room floor into lava as an excuse to jump from one piece of furniture to the next, I always turned it into acid. Sometime I'd turn it into acid-lava, if a friend was over, as a concession.
Before you pin my love of acid on the chemistry-obsessed geek I would grow up to become, I have to point out that I wasn't the first or the last person to be enamored of this mysterious class of chemical. According to Hollywood, at least, acids are still magic. As chemistry blogger Deborah Blum pointed out in her blog, Skyfall was a relatively recent example of Hollywood casting acid, as it typically does, in a villainous role
Hollywood and Hydrogen, Donors and Dollars
Another example that sticks in my mind is a scene in the 1999 film The Mummy, where a gaggle of workers opening a tomb are horrendously melted by "pressurized salt acid." This got a laugh out of me in the theater. Salt acid is most likely a reference to hydrochloric acid, HCl in chemical shorthand. HCl isn't that dangerous. There's a caveat here, obviously. I'm not saying that you should run out and jump into a swimming pool full of it. It is dangerous. When I say it's not that dangerous, meaning it's not as dangerous as it is made out to be in The Mummy. Concentrated hydrochloric acid in the eyes will probably blind you if you don't have access to water and healthcare. But just getting some on your skin won't melt it off instantaneously.
Acids are really just a peculiar class of generous chemicals that under certain conditions, want to give you a hydrogen ion- a proton. That's it. Beyond that, acids are extremely varied. In fact, it's a little unfair to lump them all together. It's a little like taking every person in the United States who is willing to donate a dollar to charity, and saying, "All these people are the same." Especially when you consider that a lot of those people may be willing to donate a dollar only to specific charities, or that people who normally wouldn't donate anything would if the cause was powerful enough.
Acids are acidic relative to things that less acidic. Whether something wants to give a proton is measured just as much by how badly the other substance it interacts with wants to take a proton. This makes perfect sense if you think about it: How do you measure how reactive something is, unless you know what it's supposed to react with? Going back to the charity analogy, how do you know how willing you are to donate a dollar, unless you know to whom you're donating that dollar?
In fact, isn't everyone with a dollar a potential dollar-donor? If you're guessing that means that anything that has a hydrogen atom in it can be a potential acid, you're on the right track. If you're really astute, you've already thought about it and realized that water has hydrogen, so could it be an acid? Go back up to the last paragraph, "Acids are acidic relative to things that are less acidic." So the answer is yes, water is acidic, compared to something like sodium hydroxide, which much less acidic than water. In fact, we use water as a baseline for acidity, and say that anything less acidic than water is a base, and anything more acidic is an acid. What are bases? How are they related to acids? I want to cover that in its own post. For now, just know that acidity hints at something much larger in chemistry: Reactivity.
I realize that by explaining how acids work, and how just about anything with a hydrogen atom on it can be acidic, I've taken away a little of the magic. While knocking it off the list of universally sexy, Brendan Fraser-endangering substances, acids are still quite fascinating and dangerous in their own way. So let's put some real magic back in.
Working In the Lab, Late One Night
Here I steal an anecdote directly from my high school biology teacher. When she was in grad school, she was working in a lab with someone who regularly left behind a mess in the lab and never cleaned up after herself. My biology teacher took it upon herself to clean up after this person. Maybe it's because she was more of a biologist than a chemist, but she had a lapse in judgement. She picked up a large glass bottle with what, from her description, sounded like about 500 mL of concentrated sulfuric acid sloshing around the bottom of it. She decided to get rid of it, and to dilute it first. She put it under the faucet, poured a fair amount of water into it, capped it, and proceeded to shake it around a little. The chemists reading this are now sitting up in their chairs with interest. She said she shook it once, twice, and before she could bring the bottle down for a third shake, it exploded.
Glass was everywhere, she was bleeding from some cuts, and she was frozen, staring at the remnants of the bottle in her hand and thinking, "Oh, right... exothermic."
If you want to try your own experiment at home. Here's one you can try. Don't worry, nothing will explode disastrously. At worst, you'll make a slight mess in your kitchen.
1. Get a Styrofoam cup, with a lid.
2. Get a reasonably accurate lab thermometer (they're on the internet, they're cheap, and most don't contain mercury.)
3. Get some room temperature water.
4. Get some room temperature white vinegar from the grocery store (it's an acid).
Fill the cup about halfway with water and stick the thermometer through the lid of the Styrofoam cup- or calorimeter (because that's what you've just built.) Check the temperature. The water should be close to the temperature of the room, if it's been sitting out for a bit. Check the temperature of the vinegar, then pour some vinegar in the water. I'm not going to say in what amounts. It's science: Experiment. See what you find.
I think you'll see that the temperature of the water will change. Isn't it odd that two substances of the same temperature will spontaneously heat up?
Got baking soda? Go ahead. Play around with that, just remember that baking soda and vinegar tend to foam up and make a mess. I'm not in the business of telling you what to do. Just don't be stupid and pour vinegar in your eyes, or step on the thermometer with your bare feet. I also don't recommend trying to extend this experiment beyond vinegar and baking soda if you don't know what you're doing. The advice I have for any experimenter, young or old? Buy a notebook, keep meticulous records, and erase nothing. If you make a mistake, cross it out so it's still legible. You never know when a mistake will prove valuable. Want to do some fun, safe, controlled, lab experiments at home? Buy this book.
Skulls and Crossbones
Still, I understand, you're reading this in the hope that I'm going to write something unexpected, something cool and sexy about acids. You yearn for me to tell you there's an acid out there that will do this (warning, even if you know it's just latex, it's still pretty gory.) I understand. There's something deep and dark and fascinating about a killer. Acids can be of course, dangerous and corrosive and worth being careful around for many reasons.
Strong acids will both burn you and not burn you. It's a little confusing, because highly concentrated acids will react with water in your body to release heat. This creates a thermal burn. But, what most people describe as a chemical burn, is really just chemical cellular poisoning. Strong acids will denature, or warp the proteins that are the building blocks of your cells. Either they destroy them or they twist them out of shape so that they no longer function. They will directly destroy cell membranes, essentially popping your cells open. Then, there's hydrofluoric acid.
If you want to think of acids as Hollywood villains, there are the henchmen, like hydrochloric acid, which is harmful- but you do carry around a bunch of it in your stomach. It gets used a lot in high school chemistry labs. A friend in high school got some in his eye (he wasn't wearing goggles- an unwise choice on his part) and had to wear an eye-patch for a week, but he recovered. Sulfuric acid can be pretty nasty. It's often employed by the scum of the earth to attack women in certain parts of the world. But these acids are just strong. They're burly and macho and shove things around. If you want scary, if you want a serial killer, hydrofluoric acid (HF), is one of those. HF has an acidity about one hundred times that of vinegar, but that actually means it's fairly weak. Stomach acid is about ten billion times more acidic than HF (literally, I don't just throw the word billion in there for hyperbole). Sulfuric acid is even stronger. Yet an experienced chemist, Hylton Jolliffe, had this to to say about it on his blog,
"Actually, it's just barely a gas. In a cool room it'll condense out as a liquid (it boils at about 20 degrees C, which is 68 F.) The straight liquid must really be a treat, but I've never seen it in that form, and would only wish to through binoculars."This is because the fluoride part of HF will wreak havoc on your body's biological processes. It is a protoplasmic poison-- a cell murderer, and it wreaks havoc with your body's electrical impulse system by binding to calcium, and never letting go. The worst part? Initial exposure can be painless. Victims will not realize they've been poisoned until hours after exposure, after damage is well underway. By then, Calcium fluoride crystals have solidified in their bodies, causing intense pain, and fluoride is invading the bones, stealing calcium, all while interfering with muscular function, including your heart function. Like any hazardous chemical, sulfuric acid demands respect. Hydrofluoric acid demands fear.
Avast! Ye Rum-Soaked Scurvy Dogs!
Of course, knowing that vinegar is an acid is a good hint that acids are not all so deadly. As I mentioned above, acids are as varied as people. You need ascorbic acid, for instance, to survive. Ascorbic acid is better known as Vitamin C, and unlike other certain other vitamins, we cannot make our own vitamin C, or store it. We lost that ability with our primate brethren. if you go back far enough, our ancestors likely synthesized it in their bodies. However, primates naturally have diets sufficiently high in Vitamin C, and so as they evolved, a mutation occurred somewhere along the line that meant we lost that ability. This is an example of evolution "running backwards" or rather, of the fact that evolution is not some neat, linear process. Early primates that couldn't create Vitamin C in their bodies weren't adversely affected by the mutation, at least not seriously enough to die off before they could reproduce.
Much later in history, as humans evolved and began undertaking lengthy sea voyages, this mutation came back to hurt us in the form of scurvy. The "vita" in vitamins is the Latin word for life. We require these substances to survive. Scurvy killed sailors in the early modern era (circa 1500 CE) and when citrus was discovered to ward off the effects (at the time, it was not known that ascorbic acid was the reason) it became a closely guarded military secret, since it allowed navies to extend their voyages.
Other beneficial acids? Well, I don't exactly know about beneficial, but anyone who has ever uncorked a wine bottle or mixed a bloody Mary has encountered the intoxicating effect of a weak base known to most people as alcohol. Relative to the alcohol, you are very slightly acidic.This popular and mildly addictive drug has affects your nervous system in many different ways, and there is no one effect caused by alcohol. The high you experience from alcohol isn't solely due to its interplay with your acidic properties, but these properties do play a role play a role. Actually, the acidity of alcohol and water is nearly the same. And sometimes alcohol will play the role of acid or base, depending on what it's doing in your body. This property, or acting both as acid and as base, is known as being amphoteric, and it's not all that uncommon.
There is so much more to the world of acids and bases than can be contained in a blog post. Acids are not so much interesting as a class of chemicals, as they are a reminder that the chemical universe is vast and varied. Their properties are not limited to a single number, like pH (yet another post). They kill and they save, and the dangers they sometimes present serve as a reminder that nature is can be quite the savage beast. They can get you high and they can cut you down. The central theme, the big lesson, is that a lesson in acids is a lesson that gets at the root of what chemistry is: What reacts with this? Why? How? Why do things with similar properties in one respect (the acidity of water and alcohol) behave so differently in other respects (one hydrates and the other dehydrates)? This story is the entire story of chemistry. Once you start to pull at the threads that will answer these questions, you find that the stories get a lot more complicated, and a lot more interesting.