[HN Gopher] Hydrochloric acid is more complicated than you think
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Hydrochloric acid is more complicated than you think
Author : gumby
Score : 93 points
Date : 2022-12-27 18:27 UTC (4 hours ago)
(HTM) web link (www.science.org)
(TXT) w3m dump (www.science.org)
| aabajian wrote:
| I remember a bit of this in undergrad gen chem. If pH stands for
| -log([H+]), how can pure water (H2O) have a pH of 7? In theory,
| there shouldn't be any hydrogen ions in pure water. Turns out
| there are two simplifications being made:
|
| i. H+ in aqueous solution is synonymous with hydronium ion
| (H3O+).
|
| ii. Water is in an equilibrium autoionization reaction with
| itself and the hydronium and hydroxide ions:
|
| 2H2O <=> H3O+ + OH-
|
| A pH of 7 means the negative log of the hydronium ion
| concentration is 7. Or about 10^-7 hydronium ions per liter. This
| reflects that the reaction above greatly favors water in the H2O
| state. We tend to make such simplifications (H+ for H3O+) in
| order to make teaching easier, but at some point it impedes a
| deeper understanding of what's really going on.
| dthul wrote:
| Nice bit of insight! For anyone confused like me: I believe it
| should read "about 10^-7 mols of hydronium ions per liter",
| which is about 6*10^16 ions per liter.
| vore wrote:
| Perhaps we've ended up full circle on this again as the current
| leading theory is H2O actually forms the cation
| H+*(H2O)2*(H2O)4, where the H+ forms a hydrogen bond to two
| H2Os which form two more hydrogen bonds to two H2Os each:
| https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2946644/
| nyanpasu64 wrote:
| The water memory folks will be up in arms over this
| discovery!
| aabajian wrote:
| Ha, I wonder if that structure provides any more insights
| into pH.
| A4ET8a8uTh0 wrote:
| I think my mind was first blown when our physics teacher asked
| us if H2O conducts electricity. And naturally we all said
| yeah[1]. We were naturally wrong, but pure water is amazing in
| its own right.
|
| edit: decided to add an edit just in case someone tries to test
| this claim
|
| [1]https://www.usgs.gov/special-topics/water-science-
| school/sci...
| basementcat wrote:
| Water ice is a semiconductor and can be doped, like silicon,
| to make transistors.
| https://m.youtube.com/watch?v=o61wtb7dSRA
| XMPPwocky wrote:
| This video seems to confuse semiconductors with "materials
| with a negative thermal coefficient of resistivity". Saying
| "this gets more conductive as you heat it up" does not a
| semiconductor make, as far as I understand.
| brendank310 wrote:
| Why not? It's not practical for traditional uses of
| semiconductors, but it has a mechanism to control
| conductivity.
| dvh wrote:
| Fun fact: The exact meaning of the letter p in "pH" is
| disputed, as Sorensen did not explain why he used it. Sorensen
| describes a way of measuring pH using potential differences,
| and it represents the negative power of 10 in the concentration
| of hydrogen ions. The letter p could stand for the French
| puissance, German Potenz, or Danish potens, meaning "power", or
| it could mean "potential". All the words for these start with
| the letter p in French, German, and Danish--all languages
| Sorensen published in: Carlsberg Laboratory was French-
| speaking, German was the dominant language of scientific
| publishing, and Sorensen was Danish. He also used the letter q
| in much the same way elsewhere in the paper. He might also have
| labelled the test solution "p" and the reference solution "q"
| arbitrarily; these letters are often paired. Some literature
| sources state that the "pH" stands for the Latin term pondus
| hydrogenii (quantity of hydrogen) or potentia hydrogenii (power
| of hydrogen), although this is not supported by Sorensen's
| writings. Currently in chemistry, the p stands for "decimal
| logarithm of"
| mtlmtlmtlmtl wrote:
| Interestingly this was all in the curriculum for my high school
| chemistry class.
| glasss wrote:
| I've never thought anything related to chemistry was simple, so
| if it really is more complex then I'm glad I'm in IT.
| fatnoah wrote:
| > I've never thought anything related to chemistry was simple
|
| I was an EE/CS major and getting A's in the two chemistry
| courses I took in college is one of my proudest achievements
| because I had to work so hard for them. Nothing about chemistry
| was intuitive or simple for me.
| 323 wrote:
| One thing I always wonder is what exactly does HCl dissolve in
| the stomach, and how does it not destroy the nutritional value of
| the food?
| kimmik wrote:
| Low pH is needed for pepsin to work. Also to kill some
| pathogens. Doesn't affect nutritional components of ingestion
| eg amino acids, vitamins and lipids.
| agumonkey wrote:
| makes me wonder what makes pathogen survive our stomach acid
| bath
| hammock wrote:
| No one has provided the actual answer yet. Here it is-
|
| The gastroduodenal epithelium (stomach surface) is covered by a
| sticky mucus layer into which bicarbonate is secreted by
| surface epithelial cells. This bicarbonate-mucus layer creates
| a pH gradient with a near-neutral pH at the epithelial surfaces
| in stomach and duodenum, providing the first line of mucosal
| protection against luminal gastric acid.
|
| We only learned this in the last 20 years so it's relatively
| new science
| agumonkey wrote:
| Got to learn about tooth development, and the fact that our
| cells secrete apatite to then accrete into enamel. Quite mind
| blowing the diversity of stuff our cells can emit.
| bell-cot wrote:
| > ...and how does it not destroy the nutritional value of the
| food?
|
| Acids destroying whatever they touch is mostly a "kiddie"
| version of reality. 99.9% of acids found outside of chemistry
| labs and industrial settings are no more dangerous or
| destructive ( _as acids_ ) than soda pop, lime juice, or human
| vomit (all of which are acids).
|
| The reason is that some far stronger and/or more dangerous
| acids _occasionally_ show up in household settings. Example:
| "battery acid", splashed on the skin, can cause horrific &
| life-long damage in seconds. Teaching kids to stay far away
| from anything labeled "Acid" is kinda like teaching 'em not to
| play with fire.
| thaumasiotes wrote:
| > 99.9% of acids found outside of chemistry labs and
| industrial settings are no more dangerous or destructive (as
| acids) than soda pop, lime juice, or human vomit (all of
| which are acids).
|
| > The reason is that some far stronger and/or more dangerous
| acids occasionally show up in household settings. Example:
| "battery acid", splashed on the skin, can cause horrific &
| life-long damage in seconds.
|
| I had to look up "battery acid"; turns out it's sulfuric
| acid, which is well known to be very dangerous.
|
| Of course, so is hydrochloric acid, which is the acid in
| human vomit. The destructiveness of the solution is not
| determined by the acid -- we use HCl _because_ it is
| extremely destructive! -- it is determined by the acid 's
| concentration.
|
| Note that vomiting more than a normal amount (say, because
| you're bulimic) will cause noticeable acid damage to your
| teeth.
| pjc50 wrote:
| The nutritional value is things that don't react with HCl at
| low concentration, especially amino _acids_.
| adrian_b wrote:
| Free text of the research paper:
|
| https://chemrxiv.org/engage/chemrxiv/article-details/6353634...
| gus_massa wrote:
| I recommend to take a look at the research paper because it has
| a few drawing that show how the Cl- and H+ [1] are connected
| with the molecules of the solvent. I like Lowe's post very
| much, but this really need a few graphics.
|
| [1] Note that the H+ is never alone. It's too difficult to
| remove that electron from the Hydrogen, so H+ is a shorthand
| for something more complicated.
| rolph wrote:
| typically H+ in aq. is H3O+ [hydronium]
|
| https://en.wikipedia.org/wiki/Hydronium
|
| oxygen has greater electronegativity than hydrogen thus
| oxygen takes a greater share of the electronic orbital,
| becoming a net positive region
| rolph wrote:
| actual title == Acid Personalities
|
| https://www.science.org/content/blog-post/acid-personalities
| aj7 wrote:
| Many people have never seen stainless steel rust. I have. At a
| slightly leaky Swagelok compression fitting on the HCl-containing
| gas mixture bottle for a XeCl excimer laser. The leaking HCl
| combines with the room humidity to make an acid that will rust
| stainless. And it's brown oxide rust, induced by the stripping of
| protective oxides by the HCl.
| ace2358 wrote:
| Remember, it's stain LESS not stain FEEE. It merely stains less
| than regular steel. Not that it is unable to stain at all. Haha
| I remember when I first realised that.
| colechristensen wrote:
| Literally, the suffix _-less_ means a complete absence of the
| thing. It is not a synonym for _fewer_.
|
| "Stainless except for odd situations you wouldn't normally
| find messing with the oxide protective layer" isn't a very
| good marketing name.
|
| Even though it is a lie, stainless does mean the absolute.
| thaumasiotes wrote:
| > Haha I remember when I first realised that.
|
| It seemed like you were making a joke until you talked about
| "realizing" something. So on the off chance you weren't, you
| should know that "___less" and "___ free" have identical
| meaning. The -less suffix means "present in the quantity
| zero", not "present in a quantity which is smaller than some
| unspecified other quantity".
| mabbo wrote:
| Well, linguistically speaking, adding the suffix "-less" to a
| word implies "without", in English.
|
| You can be penniless, having not one penny. You can be
| homeless- not just fewer homes but by golly none at all. You
| could be endlessly fearless and remain motionless when facing
| things that aren't harmless.
|
| Doubtlessly, I've been tasteless in this reply.
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