In films, on TV, and in comic books, an "acid" is any liquid that can eat away at and completely dissolve skin and muscle, leaving only bone and sometimes not even that. Even stronger "acids" will melt steel, glass, plastic, concrete, and ultimately everything it comes into contact with. Well everything except the glass flask that it is stored in. Such liquids are almost always either a bright green or sickly yellow color. They bubble and fizz on the counter or floor when you spill them, give off visible, smoky fumes (which never seem to be harmful in their own right), and they never dissipate. If a drop of acid eats through the floor, it will continue to eat through things on the next level down, and so on. There are even some video games where puddles of this stuff can move around and try to kill you.
This stuff will usually be referred to as either "acid," "toxic waste," "poison," or simply "chemicals," unless it's given some highly scientific name at its introduction, after which it will simply be called one of the names above. Expect it to show up at least once in any work involving a Mad Scientist. If this stuff is ever spilled on a person or other living creature, say hello to the Nightmare Fuel.
In real life, acids are the broad class of substances that react with bases, transferring electrons and/or protons. The best-known such reaction is the one between baking soda (a base) and vinegar (an acid), as in the classic "Science Fair volcano". Acids are also found in certain vegetables, in citric fruits, in soft drinks, and in your stomach, dissolving food. Some acids can be dangerous, and even the mildest ones are painful if they get in your eyes, but very few are as bad as Hollywood Acid. And most of them are colourless. The most common corrosives known for being powerful are sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl) and these do not even come close to being as strong as the stuff shown in movies. There are some chemicals called "superacids" that would (the most corrosive of which is fluoroantimonic acid), but the expense and complexity involved in making them would make using them the way they are in movies impractical.
A subtrope of Hollywood Science. Compare Poison Is Corrosive and Acid Pool (when this is applied to a Death Trap). Has nothing to do with those otherkinds of acid.
Examples:
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Advertising
A gout medication ad features a man walking around with a giant flask of fluid, which shrinks to illustrate how his uric acid levels fall once he tries the medicine. Uric acid is colorless in solution or yellow when crystallized, yet the flask's contents are a sickly greenish hue.
If you don't pay attention it appears that he has quite a love for his homemade Mt Dew.
Anime & Manga
In Gantz, the Thousand Arms Buddha statue carries a vial full of acid corrosive enough to completely liquify a person in the blink of an eye, even if he's wearing the protective Gantz suit. This actually worked in the hunters' advantage, as it was the acid spilled by Sei Sakuraoka that eventually disabled the Buddha statue's regenerative ability. (Although this didn't happen until Kei Kishimoto, among others, had met their fate because of the same acid.)
Comic Books
Three Donald Duck stories by Don Rosa involved a liquid called "The Universal Solvent" that compresses the atoms of anything it comes in contact with, turning all matter into a superdense powder. In real life, unless you're an alchemist, the term 'Universal Solvent' usually refers to water...
Batman loves this stuff; it's used to kill the villain in his very first story, The Case of the Chemical Syndicate, and is the comic-book source of Harvey Dent's scars as Two-Face. Deconstructed in Dr. Scott's article on an issue where Batman counteracts The Joker's acid by spraying the target with a strong base. Hello exothermic reaction!
Film
In Tomie: Replay, Tomie pushes Yumi, the protagonist, out of the wheelchair she was in onto a floor covered in acid.
Superman III featured "beltric acid," which became super-corrosive if it heated up far enough. It ends up as a Chekhov's Gun in the final fight against the rogue computer.
The blood of the xenomorphs in the Alien movies is made of a "concentrated molecular acid" (sic) that can eat through a starship's hull but not through the body of the xenomorph itself, due to being Silicon-Based Life. It seems to have less effect on human flesh when convenient. In Aliens, Private Hudson gets some splashed on his arm when Corporal Hicks shoots a Xenomorph in the head at point-blank range, causing little more than painful burns. Drake isn't so lucky when Vasquez attempts to shoot a Xenomorph off of him. Its potency freaks everyone out; one character makes noises about "molecular acid" in Alien, and an executive speaks of "concentrated acid" in a patronizing manner in the second - they're saying, "Umm... Acid isn't supposed to do that!"
Alien vs. Predator is inconsistent with the lethality of Alien blood. A hunter's arm is seared off by a splash of facehugger blood, and another unfortunate human has his skull melted by a blast of Xenomorph blood to the face. However, the first film also presents it as mild enough to use for body scarification.
This is actually a nod to the previous AVP fluff, where the Predators are said to have antacid blood that neutralizes the Aliens' acid blood. It will damages their skin but stops once it reaches their blood.
Cube has one of the characters meet his end when a trap splashes acid in his face.
The technobabble version is used in Richie Rich, where Richie and his estate's Gadgeteer Genius use a thick, foamy white experimental corrosive, "hydrochloric dioxic nucleic carbodium", disguised as a tube of toothpaste to help break Cadbury, his butler out of jail.
In Gremlins 2 The New Batch, there is a bit with a beaker of acid labeled "Acid: Do Not Throw In Face". One gremlin throws it in the face of another, who then assumes a Phantom of the Opera mask and cape.
The goop that Jack Napier falls into in Tim Burton's Batman is astroturf-green and has the consistency of a milkshake. It's later casually described as "acid". Later in the same film, the Joker's trick flower squirts acid strong enough to eat through thick metal in seconds (when he sprays it on the bolts holding up the church bell).
The same fate befalls some nameless extras in The Mummy as well. Rick even identifies the substance as "Salt acid. Pressurized salt acid." ('Salt acid' is the period-authentic name for Hydrochloric acid.) Although, in a subversion, the acid here burns the extras rather than dissolving their skin.
The DIP in Who Framed Roger Rabbit? acts like Hollywood Acid, though it only works on Toons. It's essentially made of the solution used to clean cels (which is to say, it's a blend of powerful paint thinners), but it still is colored green and is constantly steaming.
Slightly justified. The mix of paint-thinners may very well have a green appearance, and it's not unreasonable to have it heated by the motion and such. More pain for the toon, and less viscosity.
Averted in Runaway, in which the acid sprayed by Gene Simmons' insectoid robots causes ugly black burns on the hero's skin rather than dissolving his tissues.
In Return of the Living Dead, one of the zombies gets blinded by a faceful of nitric acid, which audibly sizzles on contact with dead flesh.
Jeff Goldblum's character Seth Brundle uses his stomach acid in the 1986 Cronenberg remake of The Fly, both to externally digest food and in one stomach-turning scene, as a weapon. It's actually specified as containing digestive enzymes.
Played straight in Saw III. In the infamous "Angel Trap" scene, Kerry has one minute to grab a key (which, contrary to Jigsaw's warning, never actually dissolves) inside a beaker of highly corrosive acid and free herself from a harness before it tears open her ribcage. By the time she finally retrieves said key, her hand is horribly mangled and the acid is dark red. What makes the scene even scarier is that the key actually doesn't free her, so she still dies.
And then there's the acid in Saw VI, which dissolves a man from the inside out in about ten seconds. While the victim was injected with a large carboy full of hydrofluoric acid, which is extremely corrosive and can also cause cardiac arrest by interfering with calcium levels in the blood it would not take effect nearly that quickly or be quite so dramatic.
In Seed of Chucky, John Waters' character dies when Glen accidentally scares him, causing him to back up into a shelf in his red room, sending photo developing chemicals crashing down on him and melting his face.
The Tall Man is killed in Phantasm II when the fluid he uses to reanimate corpses is tainted with hydrochloric acid and then injected into him, melting him from the inside-out. If that wasn't improbable enough to bother all of you chemists, this somehow causes his eyeballs to explode. This may be justified as the Tall Man's physiology is alien.
In the first RoboCop movie, Boddicker's henchman Emil attempts to crush Murphy with his car, only to miss Murphy and drive straight into a tank full of corrosive toxic waste. He survives... kind of.
Stomach acid serves as this trope in the final battle of Innerspace, when Tuck Pendleton drops his pod into Jack Putter's stomach with Mr. Igoe clinging to the side. The pod survives; Mr. Igoe doesn't.
The House On Haunted Hill in 1959 had a tank full of acid in the basement as big as a swimming pool, still caustic enough to reduce human bodies to skeletons.
A janitor is killed by having his head dunked in a sink that was randomly full of acid (or some kind of corrosive chemical) in Hospital Massacre.
In Mindhunters, a quantity of acid small enough to be concealed undetectably in a cigarette is sufficient to kill the FBI trainee who smokes it. While her death might be reasonable under the circumstances, her entire body emitting vapor from, at most, a few mL of acid isn't, nor is the dropped cigarette melting its way into the ground beneath it.
Deep Rising features giant worms with stomach acids so strong that they get their nutrition by merely engulfing and digesting their prey alive. The acting effects of this are shown in one particularly gory sequence appropriately know as "half-digested Billy".
The 1985 B-grade horror flick Attack of the Beast Creatures features a whole river made of acid, which coincidentally looks exactly like normal water. When one person tries to cross it, his body gets dissolved until only the skeleton remains. It's never made clear how such a large body of highly corrosive acid came to exist, nor how the tropical rainforest on the river bank manages to prosper.
Aversion in A Darkness at Sethanon - the Tsurani Empire's homeworld has very little metal, so they have had to find other means of torture, which consist of using caustic bases to blister the skin, not acid.
In the novel of God Of War, one of the Temple Of Pandora's boobytraps is a tripwire that spills a substance so powerful that it turns the room into a sinkhole. The fumes also burn Kratos on contact.
In Discworld, the metal-dissolving aspects of this trope are applied to scumble, as well as (justifiably) to the caustic beverages favored by trolls.
In Antony Horowitz'sRaven's Gate, The Dragon is pushed into a tub of incredibly concentrated, liquid, boric acid at a nuclear power plant. By the end of her ordeal, there is nothing left of her.
In the New Jedi Order, the Jedi-hunting voxyn beasts can vomit acid (which is, unusually, not depicted as stereotypical acid, but rather mucus that happens to be strong enough to burn through faces), and their blood is both acidic and a neurotoxin.
The rogue cleaner droids in Galaxy of Fear: The Doomsday Ship can squirt acidic cleaner. No one is ever actually killed by this directly, but when The Captain is climbing and needs both hands, they attack his face, and when he tries to paw them away frantically he falls to his death.
Live Action TV
Averted in the AMC series Breaking Bad. Walter White and his partner Jesse Pinkman need to get rid of a body. Walt tells Jesse—who at this point has not yet learned to follow Walt's instructions regarding chemistry to the letter at all times—to pick up a specific type of plastic tub, because hydrofluoric acid will dissolve any other container. So what does Jesse do? Takes a shortcut and dumps it in a ceramic bathtub. The result is a very... messy hole in the ceiling (the tub being on the second floor). Since the body, at this point, is no longer recognizable as human, the result, for those who are not completely disgusted, is Bloody Hilarious.
Averted in an episode of The Lucy Show of all places. Lucille Ball and Vivian Vance attend a night-school chemistry class, and Lucy panics when she gets splashed with a very weak acid... until the instructor tells her that the stuff she got covered in was effectively harmless.
Better Off Ted had an episode which featured a biocomputer that leaked an "acid-like goo," or "ass-goo" for short that burned through several floors and desks.
Surprisingly, The X-Files gets the bit about acid vapors right. The aliens have acid blood similar to the Xenomorphs, but most of their victims die from inhaling the stuff. This may have something to do with the fact it's cheaper to film than acid eating through people's bodies.
The blood emits toxic vapours which cause swelling and reddening around the eyes and death by coagulation. It may be acidic, but that is incidental to its effectiveness.
In the Tales from the Crypt episode "99 & 44/100% Pure Horror" a woman murders her soap magnate husband and disposes the body by putting it through the machine at his factory and turning it into soap. She takes the soap home with her and uses it when she takes a shower, but to her horror the acid from his stomach starts eating away at her skin... never mind that the manufacture of soap involves adding enough lye to give the mixture a neutral to slightly alkaline pH, so the soap-making process itself should've rendered the acid harmless. (The fact that one of her husband's eyeballs was in the soap and still moving and looking at her as she died suggests that the effect is more supernatural than chemical).
The live action Batman had an inspired variant in a Riddler story when the villain gets a special wax. It is the perfect safe-cracking tool: a powerful corrosive that is potent enough that a pocketful of the stuff will quickly and silently penetrate thick steel doors or concrete walls in minutes and yet is perfectly safe to handle until you expose it to direct flame. In fact, you'd almost wonder why Riddler didn't make a bundle simply auctioning the stuff to other criminals.
In the Friday The 13th: The Series episode "Crippled Inside" a teenaged attempted rapist backs away from his apparently cured victim into a rack of various chemicals. Body Horror ensues, and one must assume that his surviving family will be getting a wrongful death settlement.
Clark Kent, in the 1950’s The Adventures of Superman series, was lowered into an enormous vat of acid by chortling villains, who then walked out to arrange their next evil deed. Naturally, Superman then emerged, his costume soaked, but unharmed. Presumably, Kent’s glasses and clothes were dissolved.
The Columbo episode "Mind Over Mayhem" features a killer who disposes of certain key bits of evidence — a wallet, file folder with papers, and a metal can containing heroin — in a vat labeled "contaminated acid". It looks like water until the items drop in and starts to boil. Which may be a case of Truth in Television since many acids look exactly like water and items dropped into the acid often give off bubbles of gas as they dissolve (albeit not usually fast enough to produce a truly "boiling" effect).
Several episodes of 1000 Ways To Die play this trope straight with various degrees of accuracy, particularly "Deep Fried", "Fools Russian", and "Caught In A Lye".
Played with in The Adventures of Brisco County, Jr.- a skeleton is found in a bathtub full of acid. The skeleton was a fake, left by the supposed victim to fake his own death. But despite only sitting about waist deep in the acid tub, the entire body was bones, which is retrospect was an early clue that it was staged.
The Doctor Who two-parter "The Rebel Flesh"/"The Almost People" is set in a facility that mines this substance, which is simply called "acid", used for unknown (but likely military) purposes. Because it's so dangerous, the actual miners are remotely-operated Expendable Clones.
The Christmas Special "The Doctor, the Widow and the Wardrobe" involves something called "acid rain", which is a lot less like real acid rain than it is like this.
Tabletop Games
Dungeons & Dragons has this as a major damage type in 4th Edition, as well as it being one of the few ways to put down a troll for good.
Earlier editions have it too, with spells such as Acid Fog, and a black dragon's Acid Breath. And whenever the stuff is illustrated, expect it to be a bright green.
A very common damage type in Mortasheen, as well as a more specific Corrosive type of damage that specifically does heavy damage to metal (Perfect for the Mecha-Mooks the game has as its main villains)
Rogue Trader has two separate chemicals availeable that work like this. One is a substance that will dissolve anything except pure silica glass, tho the reaction causes it to quickly become inert in process. The other is a Dark Eldar poison created from a Stryxis-made "universal solvent", weaponized through a clever use of contaiment fields.
Video Games
Reptile from Mortal Kombat. His fatality in Ultimate MK3 has him vomit a gallon of "acid" on his opponent, melting their flesh clear off their skeleton. He also has acid fatalities in Mortal Kombat 4 and Deadly Alliance.
The "Dead Pool" from Mortal Kombat 2.
Borderlands features "caustic" weapons that fire acid-filled rounds that dissolve armor and flesh. "Caustic" usually refers to corrosive bases, not acids.
Any falling sand clone that features acid has it behave this way. The Powder Toy has acid not only dissolve everything it touches except diamond, but it's also flammable.
The Mac game Spin Doctor had droplets of bright green acid that activated when you passed over them and chased you.
In Metroid, Brinstar is full of some kind of acid that depletes your energy by roughly twenty points per second of contact. Considering the sort of damage the power suit can endure, that makes it about as strong as 10-12M HCl. The acid is also boiling, looking at its animation, which means that, if it is HCl, the air in Brinstar must be largely chlorine gas.
Fridge Brilliance: Samus is wearing a sealed suit of Powered Armor every time she's headed down there, and nobody ever said anything about Brinstar's native lifeforms being obligate aerobes. In-universe logic would tend to argue that they aren't, given that the surface of the planet (Chozodia, Crateria) is constantly bathed in a mild acidic rain, and given that OrphanedToddler!Samus had to undergo fairly extensive genetic engineering, courtesy of the Chozo, just to survive there.
With the modifications, it was stated she could only survive unaided on the areas around the surface. Super Metroid also features "acid lava" , which is yellowish boiling liquid that is found in lower Norfair and is able to damage Samus even after she acquires the Gravity Suit (which renders her immune to damage from lava). Whether it's actually acid or not isn't clear, as "acid lava" is just the fan nickname (to differentiate it from regular lava).
Metroid Fusion and Zero mission both feature some areas with pits of bright green liquid that serves the same function as the Super Metroid "acid lava" (ie. damage Samus even when she has the Gravity Suit, which makes her immune to damage from any other liquid hazard). Interestingly, in Zero Mission the stuff only appears in Mother Brain's chamber after the self-destruct mechanism has gone off, replacing the lava pits that were there when you fought the boss.
The stuff is also a serious threat in the Metroid stages featured in the first two Super Smash Bros. games; the lava filled the pit at the bottom of the stage and constantly rose, often to the point where the only available fighting space was a tiny platform. Any character who touches it is launched skyward.
In the Monkey Island games, grog is so acidic that it dissolves the pewter mugs it is served in as well as the locks on cell doors.
In Uninvited, the servant ghost kills you by engulfing you into his "misty form", which covers you in a thick, sticky goo that turns out to be acid that not only hurts, but turns you into a "lifeless lump of flesh".
In the Flash game Crush the Castle 2, acid projectiles play the trope 100% straight. They are green and hissing, will completely dissolve almost any substance it touches, and will leak down, dissolving any objects beneath that the target point directly contacts. This can create a chain reaction which can bring down entire structures by itself. Oddly, though it can disintegrate solid iron, it will not eat through the much softer earth once it reaches down that far, and a few kinds of rock walls are impervious to it. Human targets are naturally dissolved.
Several Gauntlet games have puddles of green acid as enemies.
In the first No One Lives Forever game, KateArcher is given (among other Bond-like gadgets) small bottles of an acidic substance that dissolves a dead human body in seconds without leaving a trace. This is claimed to be because someone of Kate's size can't be expected to be able to lug around dead bodies of large men. While this helps preserving stealth in some parts of the game, Kate only has a limited amount of uses for the acid. The sequel allows Kate to carry bodies (even though her size and strength haven't changed) to hide them, although she can still get the acid. Mooks in the sequel will also have an equivalent to dispose of their dead comrades (a Russian soldier will usually say something like "Sorry, comrade, there's less paperwork this way").
The Powder Toy has this. It's pink, dissolves everything, and it's flammable.
Subverted in 8-Bit Theater. Garland has the Light Warriors (plus White Mage) tied up over a cauldron full of a hissing, bubbling green liquid - which turns out to be Mountain Dew, swapped with Garland's real acid by the Forest Imps.
In a Wonderella strip, Jokerella threatens her with citric acid (which can be harmful in its pure form, but it's not exactly Joker-level evil).
Western Animation
The Batman/Superman episode World's Finest both subverts this and plays it straight, kinda. When the Joker leaves Superman and Batman trapped in one of Luthor's laboratories (with a chunk of kryptonite slowly killing Superman), Batman begins looking for ways to escape. He finds a container of hydrochloric acid. Batman notes that while it will take a week for the acid to eat through the wall of the room they're in, it will destroy the kryptonite almost immediately.
Similarly, Superman's Anti-Kryptonite suit is supposed to be designed to resist corrosion by acid, yet is destroyed by it anyway.
In Jimmy Two-Shoes, Jimmy's "dog" Cerbee actually has acid as waste, which dissolves anything he relieves himself on.
Homer was also about to quaff a beaker of acid, but it was knocked out of his hand by Frank Grimes. It splashed all over the wall, creating a hole big enough to drive a car through. Grimes was then chewed out by Mr. Burns for destroying the wall.
And for wasting his precious acid.
In another episode heavy pollution had covered Springfield in Hollywood Acid Rain which corroded soft materials in seconds. The effects on human flesh (and underwear) weren't so extreme, but according to Willie still "stings like a Glasgow bikini wax!"
Real Life
Real acids actually do some of the things commonly attributed to Hollywood acids. Common acids do dissolve ordinary metals, producing flammable hydrogen gas in the process(though plastic, glass, concrete, and most other common materials are unaffected). The stronger ones can also burn flesh, and produce some very nasty fumes, like smelling vinegar but far stronger. Most acids won't dissolve flesh, though, bases are actually better at this (since human bodies are slightly acidic). However, most of the common acids are clear liquids that look just like water, and they certainly don't bubble continuously for the sake of it.
Nitric acid looks like plain water until you drop in a piece of material to dissolve, at which point it eagerly plays the trope straight by boiling and bubbling as well as emitting toxic fumes. There's a reason why labs always keep beakers of the stuff under venting hoods and clearly labeled.
Hydrofluoric acid is probably the most dangerous acid someone not working in a lab could get a hold of and reasonably store. It rapidly penetrates the skin and proceeds to destroy the human body from the inside out by reacting readily with calcium. To make matters worse, because calcium is used in the propagation of action potentials (those thingamajigs that let you feel pain), many people don’t realize they’re dying until it’s too late. Standard handling procedures usually require full Hazmat suits.
Also, it's poisonous, when it reaches the blood stream and it doesn't become less corrosive nearly as fast as other acids when diluted.
Hydrofluoric acid is also unique in that it corrodes glass and metal oxides, making it notoriously hard to store.
The term Super Acid is used for any material that is more acidic than 100% pure sulphuric acid. For example, some particularly corrosive chemicals can protonate and dissolve hydrocarbons, something that does not occur in a normal acid environment.
Chlorine trifluoride - not technically an acid, but it burns through flesh, glass, rock and concrete like nobody's business. When mixed with water it explodes and forms hydrochloric and hydrofluoric acids as byproducts. Too nasty even for Those Wacky Nazis.
"It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water — with which it reacts explosively. It can be kept in some of the ordinary structural metals — steel, copper, aluminium, etc. — because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminium keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes."—John D. Clark, Rocket Scientist. As quoted here.
Lye (sodium hydroxide), which is actually an alkaline base, can cause this. One of Southern Railway's repair shops, now the North Carolina Transportation Museum, had such an incident:
"Accidents at Spencer Shops harmed workers as well as equipment. Spencer did have its human tragedies, although they were rare enough to achieve near legendary status. Perhaps the worst occurred in 1911, when a young apprentice fell into a pit filled with caustic lye used for cleaning locomotive parts. He left behind much of his skin when he was fished out but remained alive for several hours in extreme agony before dying. The tale passed from generation to generation as a warning that one should be constantly aware of safety at the shops."
