Please consider, for a moment, the 1999 Twentieth Century Fox movie "Fight Club." You know that movie, don't you? Edward Norton as the unnamed narrator? Brad Pitt as the seductive subversive, Tyler Durden? Helena Bonham Carter playing a deliciously deviant psycho chick? Lots of sweaty men beating the crap out of each other? Homemade explosives for fun and mayhem? If you've never seen it, I strongly advise watching it.
I would draw your attention to a particular scene that begins approximately 61 minutes and 11 seconds into the movie where, in the rundown kitchen of a rundown house on a rundown street the characters played by Norton and Pitt are making soap. The scene starts with a history lesson and ends with a patch of burnt flesh.
"This is Lye."
Lye, also known as sodium hydroxide or caustic soda, is typically sold as a powder and can be purchased in many hardware stores or online without much fuss. Each sodium hydroxide molecule is made up of one sodium atom (Na), one oxygen atom (O) and one hydrogen atom (H), written by chemists as NaOH. In solution, lye is highly alkaline meaning it has a very high pH (percent hydrogen) value.
Higher pH, between 7 and 14 = alkaline like baking soda
Lower pH, between 1 and 7 = acidic like vinegar
pH of 7 = neutral like water or human blood
Concentrated sodium hydroxide is one of the most powerfully alkaline chemicals you'll ever encounter. An alkaline solution is also known as a "base" which is the opposite of an acid. Remember acids and bases from science class? ("Oh boy! Lemon juice turns blue litmus paper red! Look at that! Ammonia turns red litmus paper blue! My god, this is so lame!!") A refresher on acids and bases later, but for now, back to soap...
The fancy word for the chemical process that produces soap is saponification. You get things started by performing the somewhat hazardous task of mixing a lye solution and then boiling it along with some kind of fat -- be it whale blubber, olive oil, cocoa butter, or (as in "Fight Club") the creamy, bloody flab that's been liposuctioned out of vain rich people. Unwanted byproducts are scooped away and the hot mess is then allowed to cool producing glycerin and a no-frills kind of soap that's solid or liquid depending on the concentrations of the ingredients you added.
"Can I see your hand please."
"This is a chemical burn."
Acids can be extremely useful -- like the hydrochloric acid your stomach produces to help you digest food. But mostly, we tend to think of acids as being super-dangerous chemicals. Strong acids can certainly damage your fleshy bits, but strong bases can truly wreck 'em. Your skin and soft tissues are mostly made up of weak amino acids, and when you introduce a strong base like sodium hydroxide, your skin does not come out the winner.
This is why the soap-making scene in "Fight Club" gets very lively when Tyler Durden, wearing gloves and protective glasses, pours powdered lye on his friend's hand. Lye is hygroscopic, meaning it takes in moisture from the surrounding atmosphere. Eventually, the powder poured on Norton's hand would have absorbed water from the air and gone into solution, but because the hand was moistened by the kiss, the lye immediately dissolved into solution becoming an incredibly caustic, very strong base that immediately started doing very nasty things to Norton's flesh. A man giving another man's hand a big wet kiss followed almost immediately by spasms of pain and smoking skin is so much more entertaining to the typical, jaded movie viewer than waiting for chemicals to dissolve.
At this point, it's legitimate to wonder if the concentration of the solution produced by the saliva and the powdered lye could have caused the dramatic reaction shown in the movie, but [a] I'm not about to test it, and [b] people who nitpick the science in fictional, Hollywood movies are evil and deserve lingering, horrible deaths... so we're just gonna go with the flow here.
Please consider, for a moment, this popular misconception: A lot of people think products like Drano and Liquid Plumr are strong acids that melt away clogs. Not so! Their main ingredients are strong bases that dissolve the organic matter that is usually the cause of blocked pipes. In general, clogs are mostly proteins... proteins that (like the skin holding your organs together) are mostly made of amino acids. Here is where we need to be reminded about the special things that happen when acids and bases come together.
Some of the foods we like, we like because of acid-base reactions. If the people around you aren't walking around filthy and stinking, it's because of the acid-base reactions that help give soap the power to clean. Our bodies function because of acid-base reactions. Typically, when an acid reacts with a base, you get a solution that is electrolytic, meaning it's full of ions and can conduct electricity. Not un-useful for electrically powered sacks of meat that need the energy provided by electrochemistry to breathe and shtup and write about Brad Pitt movies. Students study acid-base reactions in school because [a] teachers get to let kids play with litmus paper and see very clearly (and with reasonable safety) the effects of a chemical reaction, and [b] there are common, inexpensive acids and bases readily available so students can see that chemistry isn't like mathematics with its completely-divorced-from-a-seventh-grader's-reality mathy abstractions. And, as your science teacher may have mentioned, understanding the behavior of acids and bases is really, really, really, really, really important... but unless you were taking college-level chemistry at the age of twelve or thirteen, that point probably wasn't sufficiently hammered into your little clay-like adolescent/tweener mind.
As things in science so often do, our understanding of acid-base reactions starts with the hydrogen atom. On its own, a hydrogen atom does not have an electrical charge; it's got one negatively charged electron, and one positively charged proton that add up to a charge of zero. Take away the electron, and you've got a positively charged hydrogen ion (H+) that's basically just a proton. In an acid-base reaction, it's those protons, H+ ions, that get moved around. An acid is a substance that, in a chemical reaction, gives up a proton, and a base is a substance that takes up the proton. This is known as the Brønsted-Lowry definition of acids and bases, named after Johannes Brønsted and Thomas Lowry who suggested it in the early 1920s. This isn't the only way acids and bases are defined, but it's a very useful one when you're talking about solutions. (For now, let's skip over some stuff about aqueous solutions and hydronium ions [H3O+] and the assorted byproducts of organic chemicals interacting and focus on the essentials.)
So you have some lye, A.K.A. sodium hydroxide -- a combination of sodium atoms, oxygen atoms and hydrogen atoms in the form of sodium ions (Na+) bound to hydroxide ions (OH-). If ultra-alkaline sodium hydroxide solution gets on your amino acid-rich skin, the components of the NaOH molecules break apart, the hydroxide ions start stripping hydrogen ions out of your flesh to form new molecules, and you, you lucky duck, get to experience new adventures in agony.
Bottom line: Lye can be dangerous stuff. It's a strong base that does not mix happily with the weak acids in your skin... as demonstrated by the dramatic, searing, girly-scream-inducing reaction portrayed by Mr. Norton's character.
"What you're feeling is premature enlightenment."
Actually, what Mr. Norton's unfortunate cinematic alter ego would have been feeling was lots and lots of pain as the damaging acid-base reaction liberated electrons in the molecules of his epidermis and sent them shooting through his nervous system into his brain to announce, "HOLY FUCKING SHIT!! THIS IS CAUSING LOTS AND LOTS OF PAIN!!"
But then, Tyler Durden said this...
"You can pour water on it and make it worse, or... use vinegar to neutralize the burn."
When it comes to what to do about this sort of a chemical burn, Hollywood might be misleading us here. (Imagine!) Vinegar is a not-very-concentrated form of acetic acid (HC2H3O2). A sufficient quantity can be used to neutralize even a concentrated base like lye, but when somebody kisses your hand and pours lye on it, is vinegar really the best response? Not according to the MSDS for NaOH... not to mention The Soap Queen.
For every industrial chemical, you will find a Material Safety Data Sheet (MSDS), a summary of the dangers posed by the chemical and recommendations for what to do in case of exposure. According to the MSDS for sodium hydroxide, if you get some on you, you should flush the exposed area with water for no less than 15 minutes. The MSDS does not suggest attempting to neutralize the base (lye) with an acid (such as vinegar), even though this would seem to make sense. On this matter, mucho macho tough guy Tyler Durden gets a beat down from the MSDS as well as The Soap Queen and her court.
If you take a look at The Soap Queen's online forums, frequented by actual soap makers who have dealt with actual exposure to NaOH, they will tell you that using vinegar in response to a lye burn is definitely plan "B" because, before vinegar makes things better, it makes things way worse. Pouring vinegar on the lye will result in a chemical reaction that is exothermic, meaning energy, in the form of heat, will be one of the byproducts. The lye causing your pain and irritation will be neutralized, but relieving the chemical burn with vinegar will lead to a thermal burn that will feel just as bad before it subsides. And it certainly won't help to minimize the scar that will be left behind.
So much delightful science in one silly little movie scene! And if you really just wasted the last few minutes of your life caught up in this nonsense,
"Congratulations. You're one step closer to hitting bottom."
- Prometheans in the Lab: Chemistry and the Making of the Modern World by Sharon Bertsch McGrayne. ©2001. Published by McGraw-Hill.
- The Modern Soap and Detergent Industry by Geoffrey Martin. ©1951. Published by The Technical Pres Ltd., London.
- Biochemistry, 3rd Ed. by Lubert Stryer. ©1988. Published by W.H. Freeman and Company.
- Chemistry: The Central Science, 10th Ed. by Theodore L. Brown, H. Eugene LeMahy, Jr., Bruce E. Bursten, Catherine J. Murphy. ©2006. Published by Pearson Education, Inc.