# Are all acids corrosive, or just the strong ones? **URL:** \ **Category:** Factual Questions\ **Created:** [August 30, 2014, 8:49pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001 "2014-08-30T20:49:19Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [August 30, 2014, 8:49pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/1 "2014-08-30T20:49:19Z")
Someone claimed that urine has no leaching/corroding effect on surfaces like plastic or metal, because it is a “weak acid” (uric acid.) But don’t ALL acids corrode? Shouldn’t it only be a matter of relative strength? And don’t bases corrode as well, more or less in intensity? ---
**Author:** ![Bijou\_Drains](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bijou_drains/32/2814_2.png) [@Bijou\_Drains](https://boards.straightdope.com/u/Bijou_Drains)\ **Post date:** [August 30, 2014, 8:54pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/2 "2014-08-30T20:54:10Z")
Urine is 95% water and has no acid. It has urea. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [August 30, 2014, 9:11pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/3 "2014-08-30T21:11:35Z")
yes acids are corrosive and it depends on strength and if the substance will react with acids. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [August 30, 2014, 10:05pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/4 "2014-08-30T22:05:45Z")
Urea and uric acid are not the same substance. Uric acid is a weak acid and is not very soluble in water. It is not found (in appreciable quantities, anyway) in mammalian urine (there is a lot of it in bird poop, though). Urea is not an acid (I think it is actually weakly basic), is soluble, and is found in human and other mammalian urine. They are not even chemically very closely related. I think the similarity in names just reflects the fact that they are the main route for nitrogen excretion in mammals and birds respectively. All acids have the potential to be corrosive, with, in general, strong acids being much more so than weak ones. Pretty much all metals are attacked by acid solutions, but other substances such as glass and many plastics are not significantly affected even by most strong acids (although hydrofluoric acid will attack even glass). Yes, strong bases are corrosive too, and, like strong acids, will burn skin and flesh. ---
**Author:** ![picunurse](https://avatars.discourse-cdn.com/v4/letter/p/7bcc69/32.png) [@picunurse](https://boards.straightdope.com/u/picunurse)\ **Post date:** [August 30, 2014, 10:11pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/5 "2014-08-30T22:11:10Z")
All acids are oxidizers\*. Oxidizers are corrosive. Over time all oxidizers will destroy whatever they are oxidizing. \*There is rapid oxidation, like fire, (fuel, oxygen, igniter) and slow oxidizers like H[sub]2[/sub]SO[sub]4[/sub]. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [August 30, 2014, 10:23pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/6 "2014-08-30T22:23:01Z")
slow is a relative term. you can watch H2SO4 oxidize things like paper, hair or cloth in seconds. not as fast as fire but plenty quick. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [August 31, 2014, 1:17am UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/7 "2014-08-31T01:17:15Z")
> [@picunurse](#): > > All acids are oxidizers\*. Oxidizers are corrosive. Over time all oxidizers will destroy whatever they are oxidizing. > \*There is rapid oxidation, like fire, (fuel, oxygen, igniter) and slow oxidizers like H[sub]2[/sub]SO[sub]4[/sub]. Well, there are two not terribly closely related senses of “oxidation” in play here. Fire is oxidation in the sense of combination with oxygen. Acids oxidize something [in the sense of removing electrons from it](http://en.wikipedia.org/wiki/Redox), and oxygen may not be involved at all. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [August 31, 2014, 5:29am UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/8 "2014-08-31T05:29:02Z")
Not all strong acids are corrosive to all materials. For example concentrated sulfuric acid will passivate carbon steel and is stored in carbon steel vessels. ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [August 31, 2014, 12:34pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/9 "2014-08-31T12:34:11Z")
Corrosion is a chemical reaction that will be specific to the materials involved. Thus generalities like “all acids corrode” don’t make sense. Acids are not defined by their ability to corrode. They are electron acceptors, often by having an easily releasable proton. That will often result in oxidation of metals. But not always. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 1, 2014, 4:47pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/10 "2014-09-01T16:47:03Z")
How corrosive an acid is and how strong it is are basically unrelated. Hydrochloric acid is one of the strongest acids, but if you spill some on yourself, it’s no big deal: You walk over to the sink, rinse it off, and at worst you might have a very slight rash the next day. Nitric acid and sulfuric acid are both nearly as strong as hydrochloric, but significantly more corrosive to flesh: Spill one of those on yourself, and you’re likely to get a pretty bad burn. Hydrofluoric acid, meanwhile, is a weak acid, but if you spill some on your hand, you’d better get used to the nickname “Lefty”. ---
**Author:** ![M.Constant](https://avatars.discourse-cdn.com/v4/letter/m/3ab097/32.png) [@M.Constant](https://boards.straightdope.com/u/M.Constant)\ **Post date:** [September 2, 2014, 2:55pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/11 "2014-09-02T14:55:04Z")
> [@picunurse](#): > > All acids are oxidizers\*. Oxidizers are corrosive. Over time all oxidizers will destroy whatever they are oxidizing. > \*There is rapid oxidation, like fire, (fuel, oxygen, igniter) and slow oxidizers like H[sub]2[/sub]SO[sub]4[/sub]. Charlie was a Chemist, but Charlie is no more. What Charlie thought was H20, was H2SO4. Somebody had to say it… ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [September 2, 2014, 3:06pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/12 "2014-09-02T15:06:29Z")
“Corrosive” and “strong” are problematic terms, both being relative. Everything is to some extent corrosive, even water with a perfect pH of 7, which will corrode many (if not all) materials given sufficient time, and many compounds (like salt or sugar) very quickly. In the apparent context of the OP’s question, “strong” would be defined as “having relatively large corrosive capacity”, so the question is like a tautology: “Are strong acids strong”? Unless “strong” is defined as “low pH” or some other value. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [September 2, 2014, 4:23pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/13 "2014-09-02T16:23:47Z")
> [@jtur88](#): > > “Corrosive” and “strong” are problematic terms, both being relative. Everything is to some extent corrosive, even water with a perfect pH of 7, which will corrode many (if not all) materials given sufficient time, and many compounds (like salt or sugar) very quickly. > > In the apparent context of the OP’s question, “strong” would be defined as “having relatively large corrosive capacity”, so the question is like a tautology: “Are strong acids strong”? Unless “strong” is defined as “low pH” or some other value. But to a chemist, “strong” has a precise definition - and, as alluded to by **Chronos** a couple of posts ago, this doesn’t necessarily dictate how nasty something is. I didn’t know that conc. hydrochloric was so relatively innocuous, but as he says, hydrofluoric, as well as being able to etch glass, does hideous things to human flesh and bones despite its official status as a weak (_sic_) acid. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [September 2, 2014, 5:18pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/14 "2014-09-02T17:18:26Z")
Boric acid, H3BO3, is dissolved in water and used as an eyewash. That would hardly be corrosive. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [September 2, 2014, 5:32pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/15 "2014-09-02T17:32:13Z")
it might be corrosive to something. not every use of an acid is because it’s corrosive. some acids are useful because they taste sour. ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [September 2, 2014, 5:39pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/16 "2014-09-02T17:39:41Z")
> [@dougie\_monty](#): > > Boric acid, H3BO3, is dissolved in water and used as an eyewash. That would hardly be corrosive. Dissolved, but not dissociated. Boric acid is a weak acid. It’s not actually very soluble though unless you add borax. ---
**Author:** ![bordelond](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bordelond/32/150_2.png) [@bordelond](https://boards.straightdope.com/u/bordelond)\ **Post date:** [September 2, 2014, 7:28pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/17 "2014-09-02T19:28:57Z")
> [@Chronos](#): > > How corrosive an acid is and how strong it is are basically unrelated. Hydrochloric acid is one of the strongest acids, but if you spill some on yourself, it’s no big deal: You walk over to the sink, rinse it off, and at worst you might have a very slight rash the next day. Nitric acid and sulfuric acid are both nearly as strong as hydrochloric, but significantly more corrosive to flesh: Spill one of those on yourself, and you’re likely to get a pretty bad burn. Hydrofluoric acid, meanwhile, is a weak acid, but if you spill some on your hand, you’d better get used to the nickname “Lefty”. Interesting. Setting aside acidity, what accounts for these differences in reaction to flesh? ---
**Author:** ![Suburban\_Plankton](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/suburban_plankton/32/219_2.png) [@Suburban\_Plankton](https://boards.straightdope.com/u/Suburban_Plankton)\ **Post date:** [September 2, 2014, 7:51pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/18 "2014-09-02T19:51:21Z")
On the other end of the spectrum, a substance certainly doesn’t need to be an ‘acid’ to be ‘corrosive’. Try washing your hands with a nice strong sodium hydroxide solution; with a pH of 12-14 it’s about as far from an ‘acid’ as you can get, but it’s certainly corrosive to human skin (also to aluminum, and to a lesser extent, glass). ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [September 2, 2014, 7:52pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/19 "2014-09-02T19:52:19Z")
The specific corrosion mechanisms can involve many different reactions: complexations, redox… A solution of acid in water has three things which can attack something (let’s say flesh): a concentration of H+ which is higher than for pure water (aka “low pH”), the anion of the acid, and (for weak acids) the undissociated acid. Simplifying a lot, Cl- is quite corrosive to some metals, not so much to flesh (if it was, we wouldn’t be able to eat salt in the amounts we do). F- is what makes FH nasty to flesh; it’s also the reason it’s capable of attacking quartz (which is how the “traditional”, no-electrical-machines-involved methods of identifying that a solution contains appreciable amounts of F- work: if your acidic solution attacks quartz, you have fluorides). In their case, the corrosive mechanisms aren’t linked to the protons as much as to the anions. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [September 2, 2014, 8:14pm UTC](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001/20 "2014-09-02T20:14:28Z")
> [@Ruken](#): > > Dissolved, but not dissociated. Boric acid is a weak acid. > > It’s not actually very soluble though unless you add borax. Asimov commented, “If the delicate membranes of the eye can stand it, you can see how weak an acid it must be.” [Next page](https://boards.straightdope.com/t/are-all-acids-corrosive-or-just-the-strong-ones/697001.md?page=2)