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According to this article on Live Strong,

children have an average saliva pH of 7.5, while adults tend to be more acidic, with a saliva pH of 6.5 or lower.

Even though a pH of 6 is not very acidic, would someone be able to burn a hole in wood, for example, by applying enough saliva to it? Would the low acidity of saliva do nothing to the wood? I would assume, using common sense, that this would not be possible or else we would all have holes in our mouths (ew). However, would applying enough of a sufficiently concentrated solution for enough time to wood make it possible to burn a whole through it? If this is somehow possible, what would be the necessary conditions to make it happen in real life?

Thanks a lot in advance for any responses. All are greatly appreciated!

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    $\begingroup$ Given enough time (thousands of years), wood mostly would disintegrate by itself. Saliva will hardly make that happen any faster. 6.5 is not that acidic, after all. Water which we call "pure" is more acidic than that. $\endgroup$ – Ivan Neretin Oct 11 '15 at 15:19
  • $\begingroup$ @IvanNeretin depends on where you are and what the water contains. Otherwise true, though. $\endgroup$ – Jan Oct 11 '15 at 15:50
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    $\begingroup$ The bacteria in your saliva and the general presence of moisture would do far more to degrade the wood than any acidity of the liquid. It's still going to take years. Mechanical damage from licking (ouch ouch ouch splinters) would likely be far faster still, and you can imagine what a slow process that would be. $\endgroup$ – Jason Patterson Oct 11 '15 at 16:31
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Yes, wood is composed primarily of cellulose, which is composed of acetal linkages, and acetals are unstable in the presence of acid. Acetals are hydrolyzed in acidic conditions.

How long this would take is dependent on temperature and acid concentration, among other factors.

Also, cellulose in general is a very reduced carbon compound. Carbon prefers to be oxidized as carbon itself is not very electronegative. Carbon dioxide has a much more negative free energy of formation as opposed to cellulose. So given enough time cellulose will eventually decompose to carbon dioxide and water. This reaction must be spontaneous because the oxidation of cellulose to carbon dioxide and water is both enthalpically and entropically favorable. Breaking C-H bonds to make much stronger C=O bonds is enthalpically favorable, and the transformation of a solid to a gas and liquid are entropically favorable.

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    $\begingroup$ Cellulose has an average oxidation state of $\pm 0$. Do you honestly call that ‘very reduced’? $\endgroup$ – Jan Oct 19 '15 at 22:57
  • $\begingroup$ @Jan - acetic acid also has an average oxidation state of 0, yet its heat of combustion is -871 kJ/mol. Average oxidation state has no utility. $\endgroup$ – Dissenter Oct 19 '15 at 22:59
  • $\begingroup$ Ok, let me be more specific: the carbons in cellulose have $-\mathrm{I}, \pm 0$ and $+\mathrm{I}$. Acetic acid’s have $-\mathrm{III}$ and $+\mathrm{III}$. My standard deviation is smaller. But the point I was trying to make: I consider ‘very reduced’ to be $-\mathrm{II}$ or lower, i.e. saturated alkane. $\endgroup$ – Jan Oct 19 '15 at 23:02
  • $\begingroup$ @Jan what about carbon dioxide? It has an average oxidation state of 0 too. Would you argue that carbon dioxide is not highly oxidized? Average oxidation state is not helpful. An individual oxidation state analysis helps. And yes I agree that while the individual carbons in cellulose are not the most reduced, they are somewhat reduced and there are a lot of carbons per monomer of cellulose. $\endgroup$ – Dissenter Oct 19 '15 at 23:04
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    $\begingroup$ No, I was referring to the oxidation state of carbons averaged across all carbons. I mean, I generally agree with your answer, but the words very reduced don’t fit a sugar and put me off from upvoting. (Carbon dioxide’s carbon, of course has $+\mathrm{IV}$) $\endgroup$ – Jan Oct 19 '15 at 23:20
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Absolutely not. Wood is a plant and plants routinely have pH's between 5.5 and 6.1 So the wood would just see it as a protein rich relatively alkaline water solution. That said, the water in the saliva would help the wood rot faster if it was otherwise dry.

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  • $\begingroup$ Please elaborate as to why. $\endgroup$ – A.K. Aug 19 '18 at 22:44
  • $\begingroup$ Your aliva is a higher pH than woods internal pH, therefor the wood is acidic relative to the saliva, so the saliva is alkaline relative to the wood. Both are with in less than 1 pH of each other though. So the pH difference would not cause the cellulose to denature in and of itself. The OTHER component of spit though, the water, and possibly some of the enzymes, would damage the wood by allowing microorganisms that normally break down wood to do so more quickly. So don't spit in the house. $\endgroup$ – Anthony Bachler Aug 19 '18 at 22:54
  • $\begingroup$ In the question. $\endgroup$ – A.K. Aug 19 '18 at 23:01
  • $\begingroup$ Elaborate on what you are asking and why you are downvoting. My answer was clear and concise, i even went into more detail upon request, but your response "In the question". Makes no sense. $\endgroup$ – Anthony Bachler Aug 19 '18 at 23:05
  • $\begingroup$ I'm sorry I meant to add the information to the answer. That said concise answers are fine, but just giving the answer without the rationale is not what we strive for. Anyone is welcome to contribute answers but the aim of this site is quality and usefulness to future users (essentially we aren't Yahoo Answers). Please take a minute to look over the help center and tour page to better understand our guidelines and question policies. $\endgroup$ – A.K. Aug 19 '18 at 23:13

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