Wikipedia:Reference desk/Archives/Science/2010 September 16

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September 16

Rare earth metals

Why do the rare earth metals behave very chemically similar? Since they react almost identically to virtually all chemicals, how do manufacturers separate them from each other? --71.153.45.75 (talk) 00:23, 16 September 2010 (UTC)

See Periodic table and especially f-block. All rare earth elements share the same electronic configuration of lower orbitals (s, p, d) and differ only in their f-orbitals. Separation was very difficult in the past (fractional crystallization), but nowadays it's done by preparative column chromatography, which is quite efficient and can be easily automated. Alfie↑↓© 00:47, 16 September 2010 (UTC)

Why don't the differing f-orbitals significantly affect their chemistry? --71.153.45.75 (talk) 00:49, 16 September 2010 (UTC)

It has to do with the fact that f orbitals are relatively deep compared to the 6s and 5d valence electrons. These deep f orbitals do not participate in chemical reactions to a significant degree leading to their chemical similarity. Rigel0 (talk) 01:12, 16 September 2010 (UTC)

(edit conflict) See electron shell and sort the table by the last column "Group". The f-orbital is the the one starting with 18 electrons for Lanthanum. Chemical bond depends on the outermost shell – these electrons are farest away from the nucleus. In rare earth elements the f-electrons are shielded by these outer electrons (i.e., they don't interact with other elements forming chemical compounds). Since the number of these electrons is identical, the chemical compounds of different rare elements also show similar properties (they are essentially different only by their molecular mass). See all RE articles and have a look at the right box (Electrons per shell). You see the shell electrons: s, p, d, f,... which is 2, 8, 18, 18→32 for the lanthanides. Now click on the image. What do you get? Alfie↑↓© 01:34, 16 September 2010 (UTC)

Ten-year late clarification: only true for 4f which has no radial nodes and is relatively small. 5f is bigger and participates more, which is why actinoids are more different from each others than lanthanoids are. Double sharp (talk) 10:33, 14 December 2020 (UTC)

is bleach compatible with any Lewis acids?

I wish to guide and activate bleach oxidising's properties while at the same time making it more selective. Does adding Fe(III) chloride to bleach simply generate chlorine? (It's mostly chemistry on paper but assume I'm doing this with a fume hood.) What if I add it in conjunction with a pH buffer? (I must be really awful at literature searching ... at least for inorganic chemistry.)

I'm trying to see if I can form a coordinated H3O+ === -O-Cl+-[Fe(III)Cl3] complex and have that do any interesting reactions, like alpha-oxidation (but possibly for any other useful oxidations). Complexed hypochlorite would be less basic, right? (The H3O+ is generated from the other Fe(III) centres but we could have a buffer that kept the pH at 7. )

Google did say that adding potassium hydroxide to Fe(III) chloride and bleach (probably not in order) actually creates potassium ferrate. I'm trying to activate the bleach via the Fe(III) chloride and not the other way round. From what I know from second semester orgo, Fe(III) chloride has a high affinity for chlorides. I'm also wondering if there any good candidate reactions for cyclic transition states.

IF hypochlorite forms a complex with Fe(III) chloride, does it also encourage attack on the Cl+ like atom, if the oxygen anion is perhaps stabilised with a hydrogen bond (maybe in a cyclic transition state)?

Sometimes I read some reactions where basic conditions seem to encourage bleach's reactivity, which puzzles me, because I assume that additional base discourages hypochlorite's electrophilicity. Is hypochlorite that good of a nucleophile? John Riemann Soong (talk) 01:08, 16 September 2010 (UTC)

No is the answer to every one of your questions above. I advise you to go and read any standard inorganic chemistry textbook, section "oxidation states of chlorine", before you ever use bleach, even (in fact, especially) in your own home. Physchim62 (talk) 01:23, 16 September 2010 (UTC)

I use bleach as my primary oxidizing agent. Please do not over exaggerate the danger of chemicals to qualified personnel. --Chemicalinterest (talk) 10:52, 16 September 2010 (UTC)

I am not "overstating the dangers of chemicals", and the OP is obviously not qualified. He is ignorant of basic chlorine chemistry (whether dangerous or not), and ignorant of his own ignorance. Physchim62 (talk) 14:23, 16 September 2010 (UTC)

Don't even think about trying this at home unless properly trained in inorganic chemistry. FeCl₃ is a really nasty compound! BTW, as Physchim62 already said – would not work they way you think. Alfie↑↓© 01:43, 16 September 2010 (UTC)

The reason I said especially not at home is that JRS obviously doesn't know (or has forgotten) that acidifying bleach will simply produce chlorine gas. Unfortunately, people die every year from accidental acidification of bleach in the home. One of my favourite exam questions in undergrad inorganic chemistry is "when should you not throw up in a toilet?" (Ans: when there's bleach in it, when you should try to flush first or at least at the same time) Physchim62 (talk) 01:57, 16 September 2010 (UTC)

Not if you use acetic acid. I get reaction NaClO + HC₂H₃O₂ → HClO + NaC₂H₃O₂. --Chemicalinterest (talk) 10:52, 16 September 2010 (UTC)

ACK. I like your exam question. ;-) Alfie↑↓© 02:04, 16 September 2010 (UTC)

I am not unaware that acidifying bleach will produce chlorine under normal circumstances. But AFAIK you need a reduced chloride anion to form chlorine ... surely it's not going to take it off of chloride-hungry ferric chloride! (Though reduction of hypochlorite might produce chloride...which will be quickly gobbled up by greedy Fe(Cl3).

Furthermore I expect that complexed hypochlorite does not behave the same way as free hypochlorite. John Riemann Soong (talk) 02:48, 16 September 2010 (UTC)

Now look up the solubility product of iron(III) hydroxide, and come back when you understand the answer. Hint: you DO NOT know it already. Physchim62 (talk) 02:52, 16 September 2010 (UTC)

Well hmm, I possibly see the problem you might be talking about. FeCl3 + 3H2O ---> Fe(OH)3 + 3HCl. Would adding acetic acid prevent the production of chloride? Or just use a chloride-free Lewis acid? Don't we still have the pH buffer option? John Riemann Soong (talk) 03:01, 16 September 2010 (UTC)

I can't comment on that specific mixture but adding vinegar aka acetic acid to bleach is generally accepted as a bad idea [1] [2]. There are plenty of people commenting in the second link who've found out that it does indeed produce chlorine gas. The only exception (other then in carefully controlled laboratory situation involving people who know what they're doing) may be if you're in an emergency and need to kill anthrax spores as evidentally it's significantly more effective when acidified [3] although in such a case I would make sure it's done outside and the products are properly diluted before mixing Nil Einne (talk) 10:06, 16 September 2010 (UTC)

How does it make Cl2? Please provide a chemical reaction. --Chemicalinterest (talk) 10:52, 16 September 2010 (UTC)

Considering you two have a great interest in chemistry and I don't, I'm surprised that I'm the one who has to answer this, but from a quick search [4] (see end). It's worth remembering there's always chlorine gas being released, hence the smell, so it isn't that surprising you just have to change the equilibrium to release a resonable amount of chlorine gas. Nil Einne (talk) 11:06, 16 September 2010 (UTC)

Hahahaha heheheheheThat reaction is not balanced. I will post it here: 2 HOCl + 2 HAc ←→ Cl₂ + 2 H₂O + 2 Ac^-. I wonder what those acetate ions bond to... they can't just float around bonding to nothing. Note: Once I tried to argue that all acids + hypochlorite yield chlorine. I COULD NOT find a chemical equation for it. That's why I say that it does not make chlorine. If anyone has a better equation, please post it here.

The problem is: Chlorine is being reduced, but nothing is being oxidized. It is a redox reaction. --Chemicalinterest (talk) 14:10, 16 September 2010 (UTC)

Also, HOCl cannot become Cl2 if no chloride species are present right? If Fe(III) chloride is that much of a problem -- it would surprise me if it was, what about BF3 or B(C6F5)3? John Riemann Soong (talk) 02:53, 16 September 2010 (UTC)

Are you proposing that typical chlorine-bleach does not contain Cl^–? DMacks (talk) 03:22, 16 September 2010 (UTC)

Isn't it an equilibrium between NaOH and HOCl? Or we could add pure sodium hypochlorite powder. John Riemann Soong (talk) 03:58, 16 September 2010 (UTC)

Bleach solution exists as an equilibrium between OCl- ions and Cl2 molecules dissolved in water. See Bleach#Chemical_interactions. --Jayron32 04:07, 16 September 2010 (UTC)

Adding potassium hydroxide to iron(III) chloride would make iron(III) oxide. Dilute potassium hydroxide or potassium hydroxide/potassium carbonate solution would not work. Bleach needs to be concentrated, too. Household bleach would not work to make the ferrate.

The reaction of ferric chloride with sodium hypochlorite is: 2 FeCl₃ + 3 NaClO → Fe₂O₃ + 3 NaCl + 3 Cl₂. This reaction is assuming there is no additional acid in the FeCl3. The natural acidity of FeCl3 in neutral solution converts it into Fe2O3 and HCl. The HCl reacts with the NaClO. I am not sure whether the HCl would react with the residual NaOH in the bleach or the NaClO first.

Base makes bleach a weaker oxidant. Just react NaCl vs. HCl with bleach; the additional acidity encourages its oxidizing powers. Some things are only oxidized when they are in a basic environment. Chromates are an example. Bleach is basic, too, so this would encourage any basic reaction.

When I use bleach, I only use millimeter quantities. I have done it in a room packed with my mother's precious stuff. The chlorine or chloramine made by reacting with 1 mL of bleach is negligible. So, if you do chemistry at home, do not use beakers.

Acidifying bleach would produce chlorine gas if there is any chloride available to be oxidized. I reacted acetic acid with bleach to make the powerful oxidant hypochlorous acid, which I used to completely rust steel wool in a short time. No chlorine was made.

Typical chlorine bleach does contain some Cl^-; the production reaction is 2 NaOH + Cl₂ → NaClO + NaCl + H₂O. Chloride does not react with hypochlorite unless acidified; in base this equilibrium leans toward the right; Cl₂ ←→ Cl^- + Cl⁺. In acid, it leans toward the left. Bleach is quite basic, so the equilibrium leans far to the right.

If you read through this long post, thank you. --Chemicalinterest (talk) 11:44, 16 September 2010 (UTC)

"No chlorine was made". How can you state that? Do you know the pH you were working at? What concentration? Depending on the exact pH, you would have made some chlorine, because that particular equilibration reaction is rapid, but you might have been lucky enough to keep it all in solution.

Bleach is not produced by the "classical" reaction 2 NaOH + Cl₂ → NaClO + NaCl + H₂O, i.e. starting from preformed sodium hydroxide and chlorine. Instead, it is an electrolytic oxidation of sodium chloride, which you can visualize as forming the NaOH and Cl₂ in situ: it is similar to the chloralkali process, but without the membrane between the two compartments of the cell (and good mixing and cooling). So there is no "excess NaOH" in commerical bleach.

There is no need for additional chloride to be available for hypochlorite to give chlorine on acidification: 5HClO → HClO₃ + 2Cl₂ + 2H₂O. You should always remember that Nature might know far more chemistry than you do!

Cl⁺ does not exist in solution: maybe you are confusing charge numbers on ions with oxidation state. Physchim62 (talk) 14:24, 16 September 2010 (UTC)

I don't know what happened: Wikipedia and several other sites went down on my computer. So my responses will be shorter and curt because I wrote them before the crash and could not save them.

A nose is a very good instrument for detecting chlorine. That's what I used. ;)

There is no excess NaOH, but the hydrolysis of NaClO (similar to NH3) produces a base.

Your reaction is not balanced. Cl5+ and Cl+ cannot yield Cl⁰.

I didn't say Cl+ existed in solution; I meant the ClO^- ion. It is just a simplified version of the reaction, removing the oxide. --Chemicalinterest (talk) 15:53, 16 September 2010 (UTC)

A nose is very bad at detecting chlorine in solution (unless you're in a swimming pool)

My equation is perfectly balanced: if you don't believe me, count the atoms and the charges. 5Cl(I) = Cl(V) + 4Cl(0). Chlorine(I) (i.e., hypochlorite or hypochlorous acid) is unstable with respect to disproportionation at any pH, although the reaction is slow at room temperature if pH >8. Physchim62 (talk) 16:07, 16 September 2010 (UTC)

I see. You didn't have the → sign, and I thought it was the HClO + HClO3 → Cl2 + 2 H2O. Sorry.

Your points are correct. But I still hold to my original belief that bleach + vinegar ≠ chlorine. --Chemicalinterest (talk) 16:30, 16 September 2010 (UTC)

See thread below. --Chemicalinterest (talk) 16:46, 16 September 2010 (UTC)

Ok, well, is it possible to use chloramine as an oxidiser, in combination with a Lewis acid then? AFAIK chloramine's conjugate acid pKa is around ~2. SN2 attack on nitrogen centre, kicking out Cl- as a leaving group. I imagine if I perform this on an ether I would get a hemiaminal. John Riemann Soong (talk) 04:03, 16 September 2010 (UTC)

So the pK_a of the conjugate acid of chloramine is about 2. What does this tell you? It tells you that chloramine is a much stronger base than your ether, so it will react preferentially with your Lewis acid, negating the whole purpose of the addition.

You have already been told that THF can be oxidized by a stoichiometric quantity of bromine to give gamma-butyrolactone, which as apparantly what you want in the first place. Why on earth you want to synthesize it, I don't know, because it is a widely available industrial solvant. It can be reduced by sodium borohydride to give the hemiacetal, and this would be how any real chemist would prepare that compound, not by oxidizing THF.

If you do decide to buy some gamma-butyrolactone, make sure you have a more convincing reason for why you want it than the one you've given here: it is a precursor to GHB, a schedule 1 controlled substance in your jurisdiction of residence, so the DEA may well have some questions for you. Needless to say, we are not going to publish the recipes for "drugs of abuse from household and other easily available substances" on the Reference Desk.

Perhaps you've never heard of GHB, many people haven't. If so, you should know about it, it would be part of your chemical culture. I might suggest that if you expanded your scientific culture in general, you would need to ask fewer questions at the Reference Desk. Physchim62 (talk) 18:00, 16 September 2010 (UTC)

Uhh, the whole point of the Lewis acid is to activate the oxidiser -- not the reductant / nucleophile. Well, I thought it was obvious. :p Also, GBL isn't available in my lab, but THF is. Acetal and carbohydrate chemistry is of interest to me, plus alpha-oxidation is just pretty damn interesting.

(Also wth, GHB is controlled? But it's a simple 4-carbon compound ... how can you expect to control it? Next thing they'll think they can control the supply of ethylene glycol. Or ban the fatty acids in butter. ) John Riemann Soong (talk) 22:28, 16 September 2010 (UTC)

Organic compounds with metal ions

What's it called when an organic compound has a metal ion trapped in the center (e.g. Vitamin B12)? --71.153.45.75 (talk) 01:32, 16 September 2010 (UTC)

Organometallic complex Alfie↑↓© 01:46, 16 September 2010 (UTC)

are receptor tyrosine kinases related by homology or analogy?

I suspect most of them are analogous (that is their common structural motifs arise out of convergent evolution), unless someone can tell me the RTK family closest to the epidermal growth factor receptor family? John Riemann Soong (talk) 05:20, 16 September 2010 (UTC)

Both. The "business end," i.e. the canonical tyrosine kinase domain itself, is conserved among the various RTKs and cytoplasmic TKs but the rest of the structures are pretty divergent. So, presumably the tyrosine kinase domain emerged very early in evolutionary history and because it was so useful it became incorporated into a variety of different genes encoding cytoplasmic tyrosine kinases and receptor tyrosine kinases, resulting in the large number of tyrosine kinase gene families. Then there were gene duplication events within each family to form multiple members of each group. Here are a few references:

• [5]: A review of the protein tyrosine kinases in humans, including a phylogenetic analysis suggesting that the tyrosine kinase domain of the EGFR family is most closely related to the SYK family of cytoplasmic tyrosine kinases.
• [6]: Phylogenetic analysis of individual protein tyrosine kinase classes suggesting where gene duplication events have happened.
• [7]: Comparison of plant and animal RTKs suggesting that "that plant receptor kinases have evolved independently of the receptor kinase families found in animals" (presumably from an ancient gene encoding a tyrosine kinase domain)
• [8]: Not exactly what you're after but phylogenetic analysis of the Ig-containing RTKs.

I hope that helps you get started. --- Medical geneticist (talk) 13:14, 16 September 2010 (UTC)

Valois in South America

Transferred to Humanities

por favor quisiera saber como llega "Valois" a suramerica, concretamente a Colombia, quienes llegan al nuevo continente utilizando este apellido, si la unica heredera de la DINASTIA VALOIS no tuvo descendientes? gracias! —Preceding unsigned comment added by 190.26.158.158 (talk) 06:47, 16 September 2010 (UTC) Below is the Google translation of the above question Rojomoke (talk) 07:37, 16 September 2010 (UTC) please let me know as it comes "Valois" in South America, specifically Colombia, who come to the new continent using this name, if the only heir of the Valois dynasty had no descendants? thanks! -

I transfered this question to the Humanities desk, please see the question there. Ariel. (talk) 10:20, 16 September 2010 (UTC)

Multiple voltage splitting circuits

Hi all,

I know that using a voltage splitting circuit, I can use a known resistor on one side, my unknown resistor on the other, and measure the voltage in the middle to work out the unknown resistance.

My question is: I want to make a circuit where I can independently measure several different unknown resistances at once. I have worked out a way to do this with an equal number of known resistors (see image here), but is it possible to do it with just one known resistor? I want to simplify my circuit.

(The actual project involves multiple resistance-changing sensors, and I want my Arduino to be able to measure the resistance of each of the sensors.)

Thanks! — Sam 76.24.222.22 (talk) 12:12, 16 September 2010 (UTC)

Yes, but if you want to do it by measuring voltages, you will have to place everything in series, not in parallel: this might lead to some pretty low voltage drops, which you might not be able to measure accurately. You also have to solve a set of four simultaneous equations to get the four resistances. So the scheme you propose is simpler and more robust for practical measurements. Alternatively, you can have a single known resistance, the four unknown resistances in parallel, and you measure the current through each unknown resistor. Physchim62 (talk) 12:36, 16 September 2010 (UTC)

Hmm, while I think I can see how I could so it mathematically if I knew the currents, I don't think it would be simple to construct a circuit to measure the current at a point on a wire using an arduino... Right? I guess I'll just stick to the circuit I drew -- it's not that complicated. Thanks! — Sam 71.174.136.111 (talk) 13:27, 16 September 2010 (UTC)

The voltage across the known resistor tells you the current. What is hard about that? Edison (talk) 19:51, 16 September 2010 (UTC)

Because I need to work out the current going into each of the individual unknown resistors in the circuit Physchim62 was describing. — Sam 63.138.152.135 (talk) 20:47, 16 September 2010 (UTC)

nb. An Arduino is a single-board microcontroller and a software suite for programming it. (For those like me who were wondering) - 220.101 talk^\Contribs 20:38, 16 September 2010 (UTC)

A purely series circuit, with one known resistor in series with N unknown resistors allows you to determine the current through each circuit element via the voltage drop across the known resistor. Then the voltage drop across each unknown series resistor, combined with the known current, tells you the resistance of each unknown resistor. If each unknown resistor is in parallel with the others, you would have to determine the current in each branch. A small, known, sampling resistor in each branch circuit would be required. You cannot get something for nothing. You cannot determine the current through unknown resistors in parallel without a current measuring device, which could be the sampling resistors, or a Hall Effect current transducer, or an ammeter, or some element to tell you the current. Write the loop and node equations and see for yourself. Edison (talk) 23:59, 16 September 2010 (UTC)

Does the incubation period depends on the infected organ?

And in particular, is it possible that the incubation period of an infection of a certain organ will be shorter than the one specified in the Examples table? —Preceding unsigned comment added by 217.132.191.179 (talk) 15:09, 16 September 2010 (UTC)

Please elaborate. For some infectious diseases (e.g. rabies) the infection (bite) site affects the incubation period. However, the infected organ (the peripheral, and eventually the central nervous system) is the same in any case of rabies. What infection and what organ are you asking about? --Dr Dima (talk) 18:14, 16 September 2010 (UTC)

It's a general question, I'm not asking about a particular infection and organ. When I've wrote 'organ' I actually meant the infection site, so your answear satisfies that question. Thank you. I still wonder if the minimum of the incubation period in the Examples table is the absolute minimum, and that there is no infection sites which will reduce the incubation period, Or if there are circumstances in which the incubation period will be lower (in people with immunity depression perhaps). 89.138.126.126 (talk) 19:21, 16 September 2010 (UTC)

A quick Google search turns up a number of reports on this topic. This paper discusses a series of cases of systemic Listeria monocytogenes infection in a hospital setting (the victims were exposed to a contaminated Camembert cheese plate). The authors note that the incubation period was indeed shorter than usual, and attribute this to two factors: an abnormally high bacterial load in the contaminated foodstuff, and a severely immunocompromised patient population. TenOfAllTrades(talk) 19:40, 16 September 2010 (UTC)

"Personality disintegration"

I've heard someone use this term before, but see few reference to it in other places. Is it a real psychological thing, or made up? "Exact words were "final stages of personality disintegration." 204.184.80.26 (talk) 15:22, 16 September 2010 (UTC)

It isn't an officially recognized diagnosis, but the term has been used many times in scholarly publications, dating back at least to the 1930s. Most commonly it is used in relation to schizophrenia, but also for dementia of various sorts. Looie496 (talk) 15:47, 16 September 2010 (UTC)

Looie's correct: it's a somewhat dated, semi-scholarly euphemism for 'having a mental breakdown'. The only time it would be used by a health professional is when they were unsure of an exact diagnosis, but reasonable sure that some kind of diagnosis would be made. --Ludwigs2 15:55, 16 September 2010 (UTC)

gutters

We had a new roof put on in Nov. We have been having a lot of rain recently, and noticed that the gutters are no longer working, the rain runs between the fachia board and the gutter, it is terrible, no rain water goes in the gutters. I called the roofer out, and he said that the gutters are not close enough to the fachia board. Its kind of odd that we didn't have that problem until we had the new roof put on. My son cleaned the gutters, and behind them, where he found a lot of nails, and pieces of old roofing, but the water still does not run into the gutters, he even made sure that the gutter was tight against the fachia. What do you think the problem could be? Thanks! --Kj650 (talk) 16:02, 16 September 2010 (UTC)

When did you have this new roof put in? And how long have you had this problem? Someone posted the exact same message over a year ago at www.5min. com/Video/Fixing-a-Leak-in-the-Gutters-19945133 (blacklisted site) [9] (archival copy). Nil Einne (talk) 16:47, 16 September 2010 (UTC)

I'd contact the original roofer and ask them to rectify the problem. When they put the roof on, they should have checked to make sure the runoff went into the guttering correctly. If they don't play ball - well you have options after that such as legal action. Exxolon (talk) 01:13, 17 September 2010 (UTC)

The roofing should overshoot the fascia board so that water enters the guttering first without touching the fascia board. If you can't get the roofers to correct the error (assuming that the problem is as I imagine), then a strip of thick plastic from under the roofing to overlap the edge of the guttering would provide a temporary solution. Dbfirs 13:24, 17 September 2010 (UTC)

Did you check to see if the downspouts were clogged? —Preceding unsigned comment added by 165.212.189.187 (talk) 17:15, 17 September 2010 (UTC)

Reverse topographic prominence

My question is basically "what is the most isolated basin/lake in the world", but in a certain well-defined sense. The topographic prominence of a peak is the least you have to go down in elevation before you can ascend to a higher peak. So, define the "reverse topographic prominence" of a basin as the least you have to go up before you can descend to a lower basin (or sea level). According to this definition, the combined surface of all the oceans has the greatest reverse topographic prominence (you could define it as equal to the height of Mount Everest).

My question is, what region on Earth has the second greatest reverse topographic prominence? My first guess would be the Caspian Sea, but I have no idea if that's right. —Keenan Pepper 16:23, 16 September 2010 (UTC)

Not sure I understand. Wouldn't the greatest reverse prominence be the Dead Sea, since it is the lowest basin on Earth? Looie496 (talk) 17:41, 16 September 2010 (UTC)

In any case there are a bunch that are greater than the Caspian, including Death Valley and Great Salt Lake in the USA. My guess, though, is that the greatest is the Turpan Depression in western China. Looie496 (talk) 17:50, 16 September 2010 (UTC)

The Turpan Depression "includes the third lowest exposed point on the Earth's surface (dry Lake Ayding, -154m), after the Dead Sea and Lake Assal (Djibouti)", but that only covers exposed points. Won't the Mariana Trench contain the point of greatest reverse topographic prominence? Or are we counting liquid water as part of the topography of the surface (I had difficulty parsing that bit)? In which case, presumably the Dead Sea wins, although do we have to take into account variation in the depth of water in lakes and inland seas, once we've decided to take water as part of the topography? Second will be tricky, unless the second deepest point is half a great-circle-distance from the deepest! But we really need clarification before we can continue. 86.164.78.91 (talk) 00:18, 17 September 2010 (UTC)

Keenan's definition does not make sense to me if it is suposed to be true that "the combined surface of all the oceans has the greatest reverse topographic prominence (you could define it as equal to the height of Mount Everest)". We're supposed to be looking for the least distance that you have to go up before you go down again. Say that in some place like California or Australia where you have desert near the ocean, there is a dry depression with its floor at say 20 feet elevation, ringed by hills varying from 40 to 500 feet high. Then the "reverse topographic prominence" of the ocean is only 40 feet, because after that you can go down into this depression, unless there is a still lower such location elsewhere in the world. Clearly, dry depressions like that do exist, as well as depressions with a lake at the bottom, so while my 40-foot example is hypothetical, Mt. Everest has got to be irrelevant.

Would Keenan care to clarify what he's actually looking for? --Anonymous, 22:52 UTC, September 16, 2010.

The prominence of a peak is the height of the peak’s summit above the lowest contour line encircling it and no higher summit.

This is what I think is meant by the OP's "reverse prominence".

Is the image on the right showing what is meant here by "reverse prominence"? WikiDao ☯ (talk) 00:30, 17 September 2010 (UTC)

The image is exactly what I'm talking about. Simply the definition of ordinary topographic prominence, but turned upside down. I made a mistake in the example I gave &em; I neglected the fact that there are places lower than sea level, so the actual place with the greatest reverse topographic prominence is the Dead Sea. So, my question is, what is the place with the second greatest reverse topographic prominence, after the Dead Sea? I suspect it's not the oceans, or Death Valley or anything like that. —Keenan Pepper 02:18, 17 September 2010 (UTC)

As I wrote above, I think it's probably the Turpan Depression. You have to rise over 4000 feet to get out of that hole. I can't think of any other hole anywhere near as deep that isn't full of water. Looie496 (talk) 03:13, 17 September 2010 (UTC)

Great, that's the answer I'm looking for then. Thanks! —Keenan Pepper 04:38, 17 September 2010 (UTC)

Do all acids form chlorine from hypochlorites?

There was a thread above that brought up this question. It was never answered satisfactorily. I will post it again here to avoid cluttering of the above discussion: Do all acids react with sodium hypochlorite to form chlorine gas? --Chemicalinterest (talk) 16:48, 16 September 2010 (UTC)

I can't comment on that specific mixture but adding vinegar aka acetic acid to bleach is generally accepted as a bad idea [10] [11]. There are plenty of people commenting in the second link who've found out that it does indeed produce chlorine gas. The only exception (other then in carefully controlled laboratory situation involving people who know what they're doing) may be if you're in an emergency and need to kill anthrax spores as evidentally it's significantly more effective when acidified [12] although in such a case I would make sure it's done outside and the products are properly diluted before mixing Nil Einne (talk) 10:06, 16 September 2010 (UTC)

How does it make Cl2? Please provide a chemical reaction. --Chemicalinterest (talk) 10:52, 16 September 2010 (UTC)

Considering you two have a great interest in chemistry and I don't, I'm surprised that I'm the one who has to answer this, but from a quick search [13] (see end). It's worth remembering there's always chlorine gas being released, hence the smell, so it isn't that surprising you just have to change the equilibrium to release a resonable amount of chlorine gas. Nil Einne (talk) 11:06, 16 September 2010 (UTC)

Hahahaha heheheheheThat reaction is not balanced. I will post it here: 2 HOCl + 2 HAc ←→ Cl₂ + 2 H₂O + 2 Ac^-. I wonder what those acetate ions bond to... they can't just float around bonding to nothing. Note: Once I tried to argue that all acids + hypochlorite yield chlorine. I COULD NOT find a chemical equation for it. That's why I say that it does not make chlorine. If anyone has a better equation, please post it here.

The problem is: Chlorine is being reduced, but nothing is being oxidized. It is a redox reaction. --Chemicalinterest (talk) 14:10, 16 September 2010 (UTC)|}

The answer is unambiguously yes. I did link to it above, but did not explain it in detail. See Bleach#Chemical_interactions which I linked to above. The equilibrium reaction shown there makes it clear that ANY source of H+ ions will push the equilibrium towards the CL2 side of the equation. H+ ions have no memory from which acid they came from; even acid salts like the aforementioned Iron (III) Chloride will generate a sizable amount of H+ ions in solution; this would be more than enough to tip the equilibrium towards the Cl2 side of the equation. Furthermore, the equilibrium is an unstable equilibrium; if the pH is sufficiently high (and sufficient is probably a pretty weakly acidic solution in this case), the reaction will convert all of the bleach to Cl2 given enough time, in an open environment. That's because Cl2 is constantly removed from the reaction in an open space, so per LeChatelier's principle, the reaction will keep producing Cl2 until the hypochlorite all but runs out. Of course, in a closed container with a sufficiently small headspace, the equilibrium will establish itself when the partial pressure of Cl2 builds up to levels which force the reaction back again. But if left in the open, the hypochlorite will eventually all run out, in the exact same way that soda pop goes flat when you leave the container open. --Jayron32 17:17, 16 September 2010 (UTC)

The equilibrium requires both H+ and Cl- ions to produce Cl2. Where to the Cl- ions come from? The bleach? --Chemicalinterest (talk) 17:45, 16 September 2010 (UTC)

(EC) I can't answer the general question but [14] appears to have what's perhaps a better explaination (see the later posts) for the reaction with acetic acid then my earlier link Nil Einne (talk) 17:14, 16 September 2010 (UTC)

(edit conflict)In your acetic acid example, by the by, the acetate will be the other half of the redox. Acetate will happily reduce to ethanol in the presence of hypochlorite. So your reaction is wrong; the acetate does not remain intact instead it reduces to ethanol. --Jayron32 17:17, 16 September 2010 (UTC)

Acetate has to oxidize, not reduce. The bleach is the oxidizing agent, being reduced. The acetate would be the reducing agent, being oxidized. I do not know organic electrochemistry so I don't know whether acetate is oxidized or reduced to ethanol. --Chemicalinterest (talk) 17:45, 16 September 2010 (UTC)

Any reasonably strong non-oxidizable acid has the potential to form chlorine from hypochlorite. Chlorine is the predominant product when the pH falls below 4.56. In the absence of chloride ions, the reaction will go at different rates depending on the acid: it is particularly rapid in the presence of chloride ions (as in commercial bleach, or by addition of hydrochloric acid), but will still go even in the complete absence of external chloride as hypochlorite can both disproportionate to give chlorate and oxidize water to oxygen at any pH. Have you never wondered why commercial bleach solutions smell of chlorine? Physchim62 (talk) 17:30, 16 September 2010 (UTC)

Yes, hypochlorites can decompose 2 NaClO → 2 NaCl + O₂. What I want is a true reaction for non-chloride acid + sodium hypochlorite → chlorine. --Chemicalinterest (talk) 17:45, 16 September 2010 (UTC)

You are saying that this reaction occurs very slowly in commercial bleach solutions? NaClO + NaCl + H₂O → Cl₂ + 2 NaOH Note: There is still a source of chloride producing the chlorine. My question again. Can chloride-free acids make chlorine from bleach? --Chemicalinterest (talk) 17:48, 16 September 2010 (UTC)

4MeCOOH + 5NaOCl → 2Cl₂ + NaClO₃ + 4MeCOONa + 2H₂O. Physchim62 (talk) 18:13, 16 September 2010 (UTC)

Disproportionation? I never heard of acid-induced bleach disproportionation. Wouldn't that be a good way to make chlorate explosives? What about 3 NaClO → NaClO₃ + 2 NaCl? That is a more accurate disproportionation reaction. --Chemicalinterest (talk) 19:46, 16 September 2010 (UTC)

That equation looks like just a combination of the two separate disproportionation reactions others have mentioned. The difference is the addition of acid, and it's pretty well-known that redox potentials are pH dependent. This is an acidic-conditions equation, so the H+ help balance it (and you can see the acetate as a byproduct...it's the non-reacting counterion to the H+). Could probably write comparable equation for alkaline-conditions, you would just have OH- somewhere, which would also look fine on paper. But to answer your specific concern, now you have heard of it. The entry for "Sodium hypochlorite" in ISBN 978-0824703530 (page 51) states "Sodium hydroxide is usually added [...] to improve stability by minimizing the hpoychlorite disproportionation to chloride and chlorate." Feel free to speculate the role of non-alkaline conditions in accelerating the reaction (redox potentials, acid catalysis, whatever), but don't use paper chemistry to say something can't/won't happen when others tell you that Nature says it does. DMacks (talk) 20:09, 16 September 2010 (UTC)

That is disproportionation to chlorate and chloride, not chlorine. That's why I fussed about the reaction. --Chemicalinterest (talk) 20:13, 16 September 2010 (UTC)

You say "Yes, hypochlorites can decompose 2 NaClO → 2 NaCl + O₂" and "Can chloride-free acids make chlorine from bleach?". Please stop and think about how silly this question sounds. You've been told many times in many ways with links to wikipedia articles that bleach can decompose to chlorine in several ways, only some of which require acid, and that bleach itself can supply chloride. DMacks (talk) 18:04, 16 September 2010 (UTC)

(edit conflict)Nil Einne, that paper was good. I see the discrepancy here: bleach vs. sodium hypochlorite. Bleach is a mixture of sodium hypochlorite and sodium chloride. According to some people's posts there, the bleach reaction goes backwards. NaOH and Cl2 are recreated. The NaOH reacts with the acid, making the sodium salt, and the Cl2 is liberated. This reaction only occurs because of the extra chloride in the bleach. So, bleach and acetic acid react to form chlorine. But do sodium hypochlorite and acetic acid react to form chlorine? --Chemicalinterest (talk) 18:05, 16 September 2010 (UTC)

Does this reaction happen? 5 NaClO + 4 H⁺ → NaClO₃ + 2 Cl₂ + 4 H⁺ + 4 H₂O. This is, according to User:Physchim62, the reaction that happens when a non-chloride acid reacts with sodium hypochlorite. --Chemicalinterest (talk) 20:10, 16 September 2010 (UTC)

Erm, I didn't quite say that! If you are at a pH higher than about 5–6 (which you have to be to have "NaClO"), the reaction is 3NaClO → NaClO₃ + 2NaCl. This is the reaction that causes domestic bleach to "go off" (or lose strength) with storage: it is slow at room temperature, but noticeable at the scale of weeks or months. The disproportionation of HClO is much much faster. Physchim62 (talk) 20:37, 16 September 2010 (UTC)

Please remember that it is my job to oil everyone's rusty inorganic chemistry skills with an occasional dispute. --Chemicalinterest (talk) 11:14, 17 September 2010 (UTC)

vandal proof remote dwelling

Some time ago, I saw a published remote dwelling design featuring exterior metal walls/covers which were [by internal levers & wheels or capstans] rolled/slid into place to cover windows, etc. The result was a two-level dwelling with an exterior of solid metal walls, like a box. A non-electric keyless door lock was the only way in.

When the dwelling is occupied, the movable exterior metal walls exposed large glass window walls on all four sides and cover fixed metal exterior walls.

Though vulnerable to graffiti, the closed dwelling is virtually impervious to fire and most hunting weapons, as well as common glass breakage using rocks or weapons.

I would appreciate your help in finding some data on this dwelling. Deafness here makes written reply best. Thanks. —Preceding unsigned comment added by 66.66.32.230 (talk • contribs) 22:03, 16 September 2010

Bad idea to leave your contact info here. I have removed it; any answers to your question will be provided here. Thanks. WikiDao ☯ (talk) 22:28, 16 September 2010 (UTC)

If there is a sheet metal shutter, it will thwart the unequipped vandal or burglar, but not someone who brings along suitable tools for breaking in. My experience has been that a vacation cabin gets broken into by kids who simply kick in the flimsy door, or jimmy open a window with a prybar, or break the glass and reach in and open a latch. A solid door and solid plywood or metal over windows might prompt a juvenile delinquent to move on to the next, and easier to break into, cabin. The metal would have to be pretty thick to stop a rifle bullet from a "hunting weapon." A 303 round is said to penetrate 40 mm of steel, a 30-06 is said to penetrate 3/8 inch steel.[15] The metal would have to be expensively thick to prevent entry if the thief had a drill, a jack, a crowbar, etc. If you build a dwelling from battleship armor plate, a thief can cut into it with a plasma torch. The more money you spend making a dwelling secure, the more incentive a thief will have to spend the effort and resources to break in, on the grounds that extreme safeguards imply treasures within. What is a "nonelectric keyless lock" and why would it be impossible to defeat it? Edison (talk) 02:51, 17 September 2010 (UTC)

I suppose your standard rotating-dial combination lock would qualify as "non-electric keyless" but a good pair of bolt cutters or a welding torch would make short work of that. The Masked Booby (talk) 07:24, 17 September 2010 (UTC)

Are you talking about these? [16], [17] They are often used to provided comfy living accommodation for site watchmen on remote sites etc. Better than a camper van. In the UK you may need to ask the local council about bylaws and things and planning permision may be required in some instances. --Aspro (talk) 10:22, 17 September 2010 (UTC)

Being shot at with "hunting weapons" is a fair way down the list of likely risks in the UK ;-) Alansplodge (talk) 23:12, 17 September 2010 (UTC)

Reversed lens

If you reverse a lens on a camera, the shorter the focal length, the greater the magnification when reversed. What is the focal length at which the focal length is the same, reversed or not? --The High Fin Sperm Whale 22:48, 16 September 2010 (UTC)

As long as the lense is symmetric, the focal length should be the same on either side, regardless of the specific value of the focal length. Rigel0 (talk) 01:51, 17 September 2010 (UTC)

A typical camera lens is optimized for a certain lens to film distance and typically a longer lens to subject distance. Reversing it might make macro photos sharper. Edison (talk) 04:06, 17 September 2010 (UTC)

Indeed: in pre-digital days (dunno about now), a popular camara accessory was the reversing ring, whose two ends mated respectively with the camera's lens mount and the lens's filter mount thread precisely in order to enable this ploy. 87.81.230.195 (talk) 11:04, 19 September 2010 (UTC)

dissolve organic compounds

So we have some bunnies and the bottom of their hutch is a metal mesh. We clean it periodically, but over time, the corners in particular, have gotten caked in a fairly hard, slightly nasty crust of fur, poop and other crud which does not come off easily because it's sort of interwoven in the mesh and stuff. So, my question is, what could I soak the mesh in that would dissolve the organic stuff off without oxidizing the mesh. Preferably something that's easy and legal to purchase please. Vespine (talk) 23:36, 16 September 2010 (UTC)

Nail polish remover? John Riemann Soong (talk) 00:04, 17 September 2010 (UTC)

Which will just be some organic solvent, probably Acetone, or maybe Ethyl acetate or Acetonitrile. I don't think that's going to do a ton of good in removing "fur, poop, and other crud". I think that you're going to have to do more than just soak it, whatever you use. I think that soap and water is going to be your best bet, but you're going to have scrub after you soak it. Buddy431 (talk) 00:27, 17 September 2010 (UTC)

I was thinking of a more industrial solution, like drain cleaner or something, but would that also oxidize the mesh? The mesh is not terribly thin, maybe 1.5mm, so I think it should survive a couple of hours in some draino, but if there was something better that didn't react with metal that would be a better option. Vespine (talk) 01:32, 17 September 2010 (UTC)

Good point. Drain cleaners are usually a strong hydroxide solution, which works well on greases and oils (breaking them down via the Saponification reaction). I don't think it should do anything to the metal (after all, they're intended to be poured down potentially metal piping), but I'm not sure how effective it's going to be against fur and stuff. Perhaps someone else with some experience in the matter can add something. Buddy431 (talk) 02:43, 17 September 2010 (UTC)

Does not drain cleaner also help with hair clogs? Take care when using it, because it tends to be nasty on your skin (i.e., if it dissolves rabbit poop, grease, and fur, it will dissolve you just as well), but that would be a good shot. --Jayron32 03:58, 17 September 2010 (UTC)

An alternative simple thing to try would be some hot water with biological washing powder. That's good at dissolving organic matter - although the challenge here might be too great. --Phil Holmes (talk) 08:55, 17 September 2010 (UTC)

If the mesh is aluminium, please do not use drain cleaner as you may see some hydrogen gas and the mesh is no more. --Chemicalinterest (talk) 11:11, 17 September 2010 (UTC)

Like this. I think it's unlikely for a cage to be made of aluminum, though (I would think stainless steel is much more likely). Buddy431 (talk) 16:57, 17 September 2010 (UTC)