Hydrochloric acid is more complicated than you think
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Re: Hydrochloric acid is more complicated than you think
#2I 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.
Re: Hydrochloric acid is more complicated than you think
#3I've never thought anything related to chemistry was simple, so if it really is more complex then I'm glad I'm in IT.
Re: Hydrochloric acid is more complicated than you think
#4I 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-…
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...
Re: Hydrochloric acid is more complicated than you think
#5One 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?
Re: Hydrochloric acid is more complicated than you think
#6Free text of the research paper:
https://chemrxiv.org/engage/chemrxiv/article-details/6353634...
Re: Hydrochloric acid is more complicated than you think
#7I 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-…
Fun fact: The exact meaning of the letter p in "pH" is disputed, as Sørensen did not explain why he used it. Sørensen 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 Sørensen published in: Carlsberg Laboratory was French-speaking, German was the dominant language of scientific publishing, and Sørensen 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 Sørensen's writings. Currently in chemistry, the p stands for "decimal logarithm of"
Re: Hydrochloric acid is more complicated than you think
#8One 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?
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.
Re: Hydrochloric acid is more complicated than you think
#9I 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-…
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...
Water ice is a semiconductor and can be doped, like silicon, to make transistors. https://m.youtube.com/watch?v=o61wtb7dSRA
Re: Hydrochloric acid is more complicated than you think
#10I 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-…
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/