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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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    $\begingroup$ Assuming highest possible pH of 0.16 M of HCl in gastric acid and that an average stomach contains about 2 L of this good stuff I roughly estimated that maximum mass of Al you can possibly digest is 2.9 g. In reality many people have acid deficiency leaving them with undissolved aluminium chunks in the stomach. There are also many other health-related issues that can influence organism's tolerance towards $\ce{AlCl3}$ and releasing heat. As a kid I accidentally swallowed little (maybe 1x1 cm) pieces of Al foil from the chocolate bar a couple of times, and it never bothered me in any way. $\endgroup$ – andselisk Aug 6 '17 at 16:44
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    $\begingroup$ I'm not sure whether to vote to close the question as too broad or as personal health question. IMO both can be applied. $\endgroup$ – andselisk Aug 6 '17 at 16:46
  • $\begingroup$ @andselisk It's neither. I'm specifically referring to the reaction between hydrochloric acid and aluminum in the stomach. The main question is simply, "is it considered dangerous, or should people worry about it". It's not broad. If I didn't cover the aspect of the question that you believe is broad, please let me know instead of voting to close, and I'd love to edit the question and add more details and specifics. It is not a personal health question, but rather a question of whether or not the reaction that would occur inside one's stomach would be significant enough to be dangerous. $\endgroup$ – Aaron Esau Aug 6 '17 at 16:52
  • $\begingroup$ @andselisk (2/2) I'm not planning on eating aluminum foil and I'm not asking it for personal health reasons. I'm just wondering if the reaction is significant enough inside our bodies to be considered dangerous. $\endgroup$ – Aaron Esau Aug 6 '17 at 16:54
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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 '17 at 17:02
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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 '17 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 '17 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. $\endgroup$ – Mehrdad Mar 27 '18 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 '18 at 13:44

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