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Okay, okay. I know that swallowing a large enough amount of any substance would be considered dangerous. That isn't the point of this question, however.

As you probably know, the stomach has hydrochloric acid in it to help digest food, and kill off some microorganisms. I suspect the swallowing aluminum foil (or a decent-sized ingot if aluminum) would be dangerous, because it reacts with hydrochloric acid exothermically to form aluminum chloride and hydrogen gas.

$$\ce{2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g)}$$

Here is a video of aluminum's exothermic and vigorous reaction with hydrochloric acid: https://youtu.be/LaaORZ0ofCY?t=1m12s

aluminum and hydrochloric acid reaction

Now imagine that going on inside your stomach. I believe that the hydrogen gas may be able to escape through the mouth, but the intense heat might evaporate water (thus creating more gas that must escape), and would burn and kill cells inside the stomach. Plus, there's always the possibility that the hydrogen gas that is escaping could ignite, and burn through the mouth (where it escaped from) and into the body.

So why isn't everyone worried about accidentally swallowing aluminum foil? Wouldn't it be considered very dangerous to do so? Is there something I'm missing or otherwise not thinking of?

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    $\begingroup$ !! SAFETY !! - Swallowing any kind of metal is STUPID. If the metal pierces your intestines then you are facing a life threatening medical emergency. // Assuming that this is strictly hypothetical, then @andselisk gave you the answer in his first comment. The hydrogen gas produced won't be dangerous. $\endgroup$
    – MaxW
    Aug 6, 2017 at 16:57
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    $\begingroup$ I think its significance depends on the health conditions and biometrics of the given individual. For the majority there shouldn't be any severe consequences -- yes, transition metals are dangerous in general, but having certain decease may amplify the effect of how digestive system reacts to heat and AlCl3. I'm afraid I cannot provide a full answer beyond average calculated amount of Al that would dissolve (and, therefore, amount of heat released). If this is fine, I can post an answer, but it won't cover the question entirely. I retracted my vote, but it all seems for me too broad anyway. $\endgroup$
    – andselisk
    Aug 6, 2017 at 17:02
  • $\begingroup$ I think the real question here is "Does Al react with gastric juice in similar way as it does with concentrated HCl solution" and the answer is "No it doesn't, you could even not notice any reaction if you used such diluted acid in lab. $\endgroup$
    – Mithoron
    Aug 6, 2017 at 19:14

2 Answers 2

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For an average healthy adult person maximum concentration of hydrochloric acid in gastric juice is $C = \pu{0.16 M}$, and on average there is $V = \pu{2 L}$ of gastric acid in the stomach, assuming it's daily secretion of roughly $\pu{1.5 L}$ and some leftovers. Considering that the acid hasn't been used for the purpose yet, and the following reaction

$$\ce{Al + 3HCl -> AlCl3 +1.5H2},\tag{1}$$

one can make an assumption that the mass of aluminium metal that can possibly be digested is

$$m_\ce{Al} = \frac{1}{3} CVM_\ce{Al} = \frac{1}{3} \times \pu{0.16 mol L^{-1}} \times \pu{2 L} \times \pu{26.98 g mol^{-1}} = \pu{2.85 g}.$$

In reality the outcome depends on the health conditions and biometrics of the given individual. People suffering from acid deficiency won't be able to digest even this amount. Larger or overweight specimen can have larger/stretched stomach, so the amount of acid and its pH may vary quite a lot.

On the other hand, having certain decease such as gastric ulce may amplify the effect of digestive system reacting to the produced $\ce{AlCl3}$ and heat. Also, aluminium(III) chloride is considered to be a neurotoxin. Acute oral toxicity ($\ce{LD_{50}}$, mouse) of $\ce{AlCl3}$ is $\pu{3805 mg/kg}$. Reaction (1) produces approx. $\pu{14 g}$ of $\ce{AlCl3}$, which is not all that bad.

As @MaxW noticed in the comments, swallowing any metal is potentially dangerous and may or may not cause unwanted effects.

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    $\begingroup$ It might also be worth pointing out that a square centimetre of relatively thick domestic foil weighs just about .06g so you would need to eat a sample of foil about 7cm square to get that much Al into your stomach. If my calculations are right that is a lot to ingest, especially accidentally. $\endgroup$
    – matt_black
    Aug 6, 2017 at 18:32
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    $\begingroup$ @matt_black yep, it seems about right, I just tried to make a spherical object out of 7x7 cm foil piece and I got a ball approx. 1 cm in diameter, which is not that hard to put into the stomach. Though I would like not to include my childhood experience to the answer as is not something objectively reliable:) $\endgroup$
    – andselisk
    Aug 6, 2017 at 18:41
  • $\begingroup$ 2L of gastric acid in the stomach? Are you sure about that? At that amount your entire stomach (and then some) would be filled with acid. $\endgroup$
    – user541686
    Mar 27, 2018 at 7:56
  • $\begingroup$ I don't understand this answer. Would the reaction caused by swallowing 3g of aluminium be dangerous or not? $\endgroup$
    – jwg
    Mar 27, 2018 at 13:44
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Things that enter the stomach are typically coated with saliva and mucus, which protects it from unwanted and uncontrolled reactions. Remember, your body isn’t a glass filled with HCl, there are other “things” there, which play a protective role. If you ever saw an animal swallowing a Christmas decoration (also made out foil) and then look how it comes out from the other end, you’d notice that it’s absolutely unchanged, which means our body has mechanisms in place to protect it from unwanted events that can throw homeostasis out of the window and cause death. Every single reaction is tightly controlled by enzymes and whenever something does not look right, it’s neutralized. Simple inorganic chemistry does not explain biological processes in full and does not give you a true picture of what is happening in the body. Whatever you learn in inorganic chemistry you’d have to relearn when you get to biochemistry as the game changes drastically. So the short answer is: if you swallow a piece of foil, it will likely not react with the stomach acid and will exit the body unchanged.

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    $\begingroup$ The problem is not that one must unlearn inorganic chemistry but that one did not learn enough inorganic chemistry in the first place to be useful in biochemistry. Enzymes require delicate balances of ionic concentrations and electrical potentials to do their regulating. $\endgroup$
    – jimchmst
    Jan 28 at 22:33

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