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Aspirin is acetylsalicylic acid. When it's exposed to water vapor, the acetyl group comes off and combines with water to make acetic acid, which is the acid in

Aspirin is acetylsalicylic acid. When it's exposed to water vapor, the acetyl group comes off and combines with water to make acetic acid, which is the acid in vinegar [1]. This happens pretty fast. An open bottle of uncoated aspirin tablets can start to smell of vinegar in a day or two, depending on the local relative humidity. If you smell vinegar when you sniff your bottle of aspirin, toss the bottle. Why? Well, the other hydrolysis reaction product (salicylic acid) removes the outer layer of the skin and is used, for example, to remove warts [2]. Not something you want in your stomach. [1] http://www.kii3.ntf.uni-lj.si/analchemvoc2/file.php/1/HTML/SPEKTRA/kinetics2.htm http://www.kii3.ntf.uni-lj.si/analchemvoc2/file.php/1/HTML/S... [2] https://en.wikipedia.org/wiki/Salicylic_acid https://en.wikipedia.org/wiki/Salicylic_acid

tossaway1 10y ago
Isn't your stomach already extremely acidic...?
- enknamel 10y ago
  Not all acids are the same. What's at play isn't only the amount of free protons but also what else is disassociating. For instance, hydrofluoric acid is considered a weak acid but it can severely burn (pretty slowly but it will get you) or even kill you. The fluoride group will consume the calcium ions in your blood and possibly send you into cardiac arrest.
- rcthompson 10y ago
  Any compound with a hydrogen ion that can dissociate in solution is technically called an acid, but that doesn't mean it's acidic properties are the most relevant.
ItsDeathball 10y ago
I had always wondered why aspirin tended to smell like vinegar and rarely helped with headaches. It's quite satisfying to have an explanation for both.
mmmpop 10y ago
Thanks, this is a great comment.
skookumchuck 10y ago
Sounds like a good argument for coating the pills.
Symbiote 10y ago
In general, expired or unwanted medicine should be taken to a pharmacy or similar for proper disposal.

tossaway1 10y ago

Isn't your stomach already extremely acidic...?

enknamel 10y ago
Not all acids are the same. What's at play isn't only the amount of free protons but also what else is disassociating. For instance, hydrofluoric acid is considered a weak acid but it can severely burn (pretty slowly but it will get you) or even kill you. The fluoride group will consume the calcium ions in your blood and possibly send you into cardiac arrest.
rcthompson 10y ago
Any compound with a hydrogen ion that can dissociate in solution is technically called an acid, but that doesn't mean it's acidic properties are the most relevant.

ItsDeathball 10y ago

I had always wondered why aspirin tended to smell like vinegar and rarely helped with headaches. It's quite satisfying to have an explanation for both.

mmmpop 10y ago

Thanks, this is a great comment.

skookumchuck 10y ago

Sounds like a good argument for coating the pills.

Symbiote 10y ago

In general, expired or unwanted medicine should be taken to a pharmacy or similar for proper disposal.