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exchemist

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Everything posted by exchemist

  1. How about thinking about city dwellers? Suppose you are in a terraced house or an apartment. How would you see that all working?
  2. The role played by atomic nuclei in chemical bonding and intermolecular attractions is to provide the potential wells that confine the electrons in their orbitals. The variety of forms of attraction between atoms arises from the ways in which the electrons in adjoining atoms behave. The "Moon model", put forward in the 1980s by Robert J Moon and apparently not taken seriously today, concerns nuclear structure. This has no impact at all on chemical bonding.
  3. This is all about the behaviour of electrons in atoms and molecules, not the nuclei. Hydrogen bonding remains I think something of an enigma. At one time there was a view that it was just a special case of an attraction between permanent dipoles, but in fact it has directional character, which seems to involve the electrons of the "lone pairs" of electrons on the electronegative atom. So there seems to be an element of electron pair sharing, as in a covalent bond.
  4. Permanant dipoles are easy to explain. You have a molecule with partial +ve charge in one place and a partial -ve charge somewhere else. The partial +ve charge will attract a partial -ve charge in a neighbouring molecule and vice versa. So it's just like the attraction between oppositely charged ions but involving only partial charges. London forces, also known as dispersion forces, arise due to "flickering, fleeting dipoles" due to motion of the electrons in an atom or molecule, which induce dipoles in the neighbouring ones. The strength of dispersion forces is greater between atoms (or molecules involving them) that have greater polarisability, which tends to mean larger atoms with a more diffuse outermost shell of electrons. As I recall, the random fluctuations in electron density that give rise to this arise from the same quantum mechanical principle responsible for vacuum fluctuations - basically another manifestation of the uncertainty principle. The name Van der Waals forces is given to all intermolecular attractions that don't involve a chemical bond. So the term includes both London (dispersion) forces and the attraction between permanent dipoles. (But it would not include hydrogen bonds, as these have some directional bonding character and are thus not entirely electrostatic dipole attractions.)
  5. The idea of an "energy particle" doesn't really make much sense. Particles have energy. They can't be energy.
  6. The blue flame sounds to me like sulphur burning. I think if you heat pyrite (FeS2) you will drive off sulphur and form FeS and then in the presence of air probably you will get iron oxides. If you add HCl you will get chlorides, which can look pale green. I suspect your first picture, after addition of acid, could be a mixture of oxides and/or hydroxides of iron plus chlorides, hence the red/brown and greenish crystals. The later pictures seem to show crystal growth - rather nice dendritic growth in some of the pics. Would that make sense of what you saw?
  7. Not that it matters, but nobody has mentioned CaO2 apart from you. My post referred to CaO. OK but I was quoting that reaction to make my point that there does not have to be evolution of hydrogen, as you were previously suggesting. Regarding the separate issue of thermal stability of these hydrated minerals, you will know better than I. However the link that @joigus provided speaks of water retention at depths of up to 200km. That seems to be what they mean by "deep" in the context of water recycling in tectonic processes. So evidently they think serpentine-type minerals can survive for a while at such depths - if the subducted slab is descending fast enough (which seems to be the key variable their paper is all about). They seem to associate "deep" retention of water with water retained beyond the island arc, i.e. not entirely returned to the surface via island arc volcanism. When you say 600C, what pressure are you assuming? As the thermal decomposition involves release of water, the equilibrium will lie further in favour of the hydrated mineral under high pressure.
  8. We would an accompanying description: a picture on its own wouldn't tell us much. What acid(s) did you react it with?
  9. Fair enough, but the link I provided also includes reaction such as : 3Mg2SiO4 + SiO2 + 4H2O → 2Mg3Si2O5(OH)4.
  10. If you have oxides you don't have to generate free hydrogen. For example CaO + H2O -> Ca(OH)2. A quick internet search yielded this: https://www.liquisearch.com/serpentinite/formation_and_petrology/serpentinite_reactions. which suggests several suites of reactions, some of which generate hydrogen and others not. I imagine free hydrogen could contribute to some of the apparently reducing conditions in some volcanism, e.g. when H2S is evolved. (The link also mentions possible reduction of carbon from carbonate to methane.
  11. This is a really interesting article. Thanks for posting. I'm going out now but will read it when I get back. But from initially scanning it, it looks as if you are quite right: they do seem to suggest a gradual net absorption, with a cycle superimposed on it.
  12. Are they being depleted, though? Volcanism returns water to the surface, after all. I would have expected that there would be equilibrium, over some sort of long term cycle.
  13. I'm not watching YouTube videos, as videos take up a lot of time to watch, compared with reading the printed word, and so many are full of crap. What are the key points the videos make? Perhaps we can discuss those.
  14. I can't think of a specific effect of the pressure of the oceans on the oceanic crust, but I have read that water may play a very important role in the convection cycle responsible for plate tectonics. My understanding is that many hydrated minerals are mechanically relatively weak (e.g. "soapy" minerals like serpentine) and that "wet" rocks can get a degree of lubrication from the presence of water as they slide past one another in faults. So it may be that water facilitates the convective motion. I have also read that the volcanism behind subduction zones is at least partly due to the water entrained by the descending slab of lithosphere, which is chemically altered by it, producing lower melting point minerals which expand and rise towards the surface, as "diapirs" of magma. I suspect it's a big subject, actually. I'm not a geologist, I'm afraid.
  15. Interesting. It seems to have quite a lot in common with the Dead Sea. Though I'm not sure whether there are geothermal springs there. What I also found interesting was to read that much of the world's lithium for batteries comes from a spodumene mine in Australia. Spodumene, apparently, is an igneous pyroxene mineral with formula LiAl(SiO3)2, (i.e. 2 silicate tetrahedra with one shared edge). Other sources - or potential sources - are brines in Chile, Bolivia and Argentina. So at least the world is not currently dependent on China or Russia for it. Furthermore it occurred to me that perhaps it could be a good mineral money-spinner for Australia, which might help some of their (numerous) dinosaur politicians to get their heads round the need to stop extracting coal. But more diversified sources would certainly seem prudent, given the difficulty in replacing Li in battery technology. Li seems unique in this role. I imagine this will be due to the small size of the Li+ ion (only the 1s shell is filled) allowing it to form intercalated compounds with carbon, CoO2 etc, reversibly.
  16. Sort of, yes. So it gives you the idea of losing electrons during oxidation. The caveat (sorry if this is teaching grandmother to suck eggs) is oxidation state is not the same as the charge on an actual ion. It's a book-keeping convention that ascribes a number and sign according to what would apply if a given compound were fully ionic. So for example in SiO2, which of course is covalent rather than ionic, Si has an oxidation state of +4 and O has one of -2. And in the present case of the sulphate ion, S has an oxidation state of +6 and the 4 O atoms -2 each. Sulphate reducing bacteria can take S from +6 all the way down to -2 in H2S.
  17. I imagine that would be due to the presence of sulphate-reducing micro-organisms in the manure, wouldn't it? I find the concept of oxidation states helps. The higher the +ve number, the more oxidised the species, which signifies the removal (whether real or notional) of more electrons.
  18. Davy, and others at the time, seem to have used a variety of names, Davy initially proposing alumium. Subsequently both aluminium and aluminum were used, both by him and others, though it's true did write a textbook using the aluminum spelling: https://en.wikipedia.org/wiki/Aluminium#Etymology It seems to have been a choice by a North American called Noah Webster, when compiling his eponymous dictionary in 1828, that settled the American spelling.
  19. I collect some in a water butt connected to a gutter downpipe, for watering calcifuge plants, that's all. But then I live in an area that is not short of water, as do many people. Statistics on who collects and who doesn't are only really relevant if they relate to areas that are short of water or projected to become so. As for sewage, what we need here in the UK is an initiative to separate sewage from rainwater runoff. Sewage is processed in sewage farms, not discharged to the sea (unless there's a problem with the treatment plant, which happens too often). Adding the volume of rainwater runoff to it, as we have done since the Victorian sewers were built, just magnifies the volume that has to be treated. It's a thoroughly bad idea. We ought to be able to run rainwater into the rivers and process sewage alone in the treatment plants.
  20. This is not exactly news, though, is it? People have done this for millennia. What's the issue for discussion here?
  21. OK I see what you mean. These nodules contain transition metal ions in low oxidation states, apparently, e.g. Mn (II).
  22. There are micro-organisms that use sulphate to oxidise carbohydrates or hydrogen to obtain energy for their metabolism, so there are circumstances in which ΔG is -ve for a reaction scheme in which it behaves as an oxidiser, being reduced to H2S in the process. But as an oxidiser for what we would regard as a chemical fuel, not really. Concentrated (i.e. not ionised) sulphuric acid is another story however: that can be a powerful oxidising agent.
  23. This post looks barking mad to me. A giant pot of tea? I don't see much point in attempting a serious answer to this nonsense.
  24. In your previous thread on this subject, the possibility of organic origin was mentioned several times. If the pyrite is of organic origin, you would expect it to contain traces of other materials. If the sample is not a pure substance, you can't expect its composition to be exactly that of a pure compound. It doesn't mean there is anything "wrong" with the chemistry of the pyrite portion of it, just that there are substances present in the sample other than pyrite. I should have thought that was obvious. I don't see anything surprising here.
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