Wikipedia:Reference desk/Archives/Science/2008 April 23

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April 23

Sodium ethoxide (organic chemistry)

In my organic chemistry class I see this reagent used in various reactions. But I never knew what the sodium is for. Why can't the reagent just be OH minus? —Preceding unsigned comment added by 128.163.171.61 (talk) 01:15, 23 April 2008 (UTC)

Sodium is just a counter ion, would be the same if it were Potassium ethoxide. Ethoxide can be used as a base in organic (non-polar) solutions where Sodium Hydroxide (OH-) would not dissolve (as well).--Shniken1 (talk) 01:18, 23 April 2008 (UTC)

(ec)It's there for the same "reason" that one talks about the reactions of "just" OH^- (hydroxide), but actually uses KOH or NaOH to get it--the K⁺ or Na⁺ is a counterion. It would be very hard to get a solution or solid that is "just" anions: each one repels all others. There were corresponding cations to balance their charge and give a net-neutral situation. DMacks (talk) 01:23, 23 April 2008 (UTC)

All the above said, ethoxide, one of the alkoxides, is often used because it is an extremely strong base, and some reactions require that level of basicity. In other reactions, such as some nucleophilic substitution reactions, the point of the reaction is to add ethoxide to another molecule through an ether-like bond. Someguy1221 (talk) 01:28, 23 April 2008 (UTC)

So counterions don't affect the actual reaction? Its only purpose is the preparation of the reagent (as mentioned by dmacks)? (original poster) —Preceding unsigned comment added by 199.76.153.227 (talk) 02:48, 23 April 2008 (UTC)

Right. You can never generate an anion without also generating a cation, and you can't remove the cation without replacing it with another one. Further, you usually actually want the counterion to do nothing, so you avoid complicating the reaction. Although you may find reactions in which both ions serve a purpose. Someguy1221 (talk) 06:47, 23 April 2008 (UTC)

Does it matter what counterion is to be used? For example, instead of NaOEt could one use KOEt? —Preceding unsigned comment added by 128.163.194.167 (talk) 15:36, 23 April 2008 (UTC)

I'd assume so not; except for a certain narrow set of biochemical interactions, and methods of seperating them, Na and K are chemically indistinguishable. Someguy1221 (talk) 17:16, 23 April 2008 (UTC)

I think Someguy1221 means that he assumes not. The counter ion should not influence the reaction much, it may only change the amount of dissociation that occurs in solution, but for Na and K the difference would be indistinguishable. This though probably won't influence the reaction because as the free EtO- is used up more of the NaEtO (or KEtO) will dissociate. So long as it is not involved in the reaction the counterion should not matter.--Shniken1 (talk) 02:15, 24 April 2008 (UTC)

Right, oops. Someguy1221 (talk) 03:34, 24 April 2008 (UTC)

(outdent) Except that the counterion very often is involved in the reaction when one looks closely. One uses bases to deprotonate other things, which usually renders those "other things" anionic, and hence they become associated with the counter-cation. It probably doesn't have much noticeable effect at the level of "here is how various functional groups react, this is the major product" and the types of reactions covered in most intro-orgo classes.

It's real though, because "the whole set of reactant molecules and ions" becomes "the whole set of product molecules and ions", not just "the basic piece deprotonating something" and the different metals have different properties. They might be better or worse at stabilizing an anion at a certain position in a molecule, for example, or have greater affinity for one or another structure. LiHMDS, NaHMDS, and KHMDS react "similarly", but when one _HMDS provides mediocre results, one often tries the others also instead of just scrapping the whole _HMDS type of bases.

Here's an interesting result: formation of the enolate of 2-heptanone can give two different enolates isomers (Δ^1,2 vs Δ^2,3). These two isomers obviously have different stabilities, and given the "more substituted double bond is usually more stable" as a first approximation, one expects to see mostly the Δ^2,3 enolate (under thermodynamic conditions). Using Li⁺ as the counterion for the enolate (i.e., reacting the ketone with a base having a litium cation), one indeed gets 87%:13% Δ^2,3:Δ^1,2. Switching to a K⁺ counterion, the thermodynamic ratio is only 58%:42% Δ^2,3:Δ^1,2 (data taken from House, Modern Synthetic Methods) The more-substituted alkene is still "more stable", but not as much more stable. DMacks (talk) 03:07, 24 April 2008 (UTC)

I have another question: In various reactions, I see -OH + H2O used. Why is the counterion omitted there? Also, there are reactions that use H3O+, but there are others with H+,H20. What's really the difference between the two acid reactants? —Preceding unsigned comment added by 128.163.224.222 (talk) 19:42, 26 April 2008 (UTC)

A strong base "fully dissociates in water", so it looks like "OH^- + something⁺" in solution (i.e., as used in a reaction). As above, when used as a base, the counterion ("something⁺") does not have a substantial effect in many reactions (it acts as a "spectator ion"), so it is often omitted on both sides of the reaction. Likewise, acids protonate water, so H⁺ in solution forms H₃O⁺. But really, that thing reacts by transferring H+ onto something else...the water molecule is a temporary location or carrier for the H+, and the overall reaction is just H+ (coming from the original acid) protonating "something". It's all a matter of being as precise and technically correct as one wants without becoming overly complicated and obscuring the important part of the reaction with those technical details. DMacks (talk) 18:23, 27 April 2008 (UTC)

Water flow in pipelines

An overhead tank, connected to 4 floors of a building, each floor consisting 4 flats, has seperate water pipe line. How is it possible to control the water pressure when the pipeline has no safety valve to control the water flow? The pipeline has individual air outlet pipe only. Thanks, Narayan. —Preceding unsigned comment added by 59.178.113.204 (talk) 02:47, 23 April 2008 (UTC)

Unless there is some type of restriction in the pipe, such as a valve, I'd expect it to have a higher pressure at the lower floors. StuRat (talk) 02:53, 23 April 2008 (UTC)

Indeed that is the case. Most domestic appliances have a very wide range of pressures they can operate on, typically 0.5 bar to 10 bar. This allows operation with either a direct supply or from a header tank, usually without valves. In certain areas some houses have very high pressure feeds and need a pressure reducing valve, for example where there is a road going up a high elevation hill. In order to give adequate pressure to houses at the top of the hill, those at the bottom have a higher pressure than is usual. This was used by Yorkshire Water to excuse a high leakage rate, they said that if they could run the system on the same pressure as the London or Anglia regions the leakage rate would be lower than average, but the high pressure they need meand their leakage was above average -- Q Chris (talk) 07:26, 23 April 2008 (UTC)

In order to comply with British regulations, each flat should have its own valve where the water enters it. Instead, the property you describe would have to be wholly disconnected in order to change a washer. - Kittybrewster ☎ 09:07, 23 April 2008 (UTC)

This is a stop valve (stopcock), not a pressure regulator, i.e. it gives you the ability to turn off the water. In some cases non-return valves may also be fitted, but generally nothing affecting the pressure [1]. —Preceding unsigned comment added by Q Chris (talk • contribs) 07:47, 25 April 2008 (UTC)

Plumbing

what is meant by airlock system in waterpipe line? How does it work to control the water pressure? Thank you. Ranee. —Preceding unsigned comment added by 59.178.113.204 (talk) 02:54, 23 April 2008 (UTC)

An airlock (a plug of air) can be created to fill a gap in the volume of water. For example as a result of a minor leak. An airlock will seek a high place, eg the top of a radiator - which you then have to "bleed" with a radiator key. You may also need to fill the system up with more water to improve the pressure. - Kittybrewster ☎ 09:12, 23 April 2008 (UTC)

Do please register a name. - Kittybrewster ☎ 09:12, 23 April 2008 (UTC)

Or are you talking about an expansion vessel?? The expansion vessel is a metal container divided in two by a rubber diaphragm. One side is connected to the pipe work of the heating system and therefore contains water. The other, the dry side, contains air under pressure and you will find a car-tyre type valve for checking pressures and adding air. When the heating system is empty or at the low end of the normal range of working pressure the diaphragm will be pushed against the water inlet. As the water expands so the diaphragm moves compressing the air on its other side and giving rise to a moderated increase in pressure that you can see on the pressure gauge. - Kittybrewster ☎ 09:26, 23 April 2008 (UTC)

Outside of heating systems, water supply pipes often contain an air pocket (or stand pipe) to prevent water hammer, an overpressure problem. Rmhermen (talk) 12:28, 23 April 2008 (UTC)

Viruses/Bacteria

Hello,

I have a question:

Why do viruses and bacteria (except the "good" bacteria) cause their host to die if left un-treated by modern medicene. I thought the whole reason a virus spread was so that it could pass on its genetic material, and yet if the host dies it is unlikely that it will be able to pass itself onto another being. If viruses were like the worms Philip J. Fry got in Futurama, and instead enhanced the host body, surely that would be a much more effective way of passing the genetic material on?

84.13.26.33 (talk) 08:15, 23 April 2008 (UTC)

Actually only a small number of viruses and bacteria are likely to kill you if left untreated. The human immune system isn't that bad. For example, many millions of people catch the flu every year, a large proportion of them don't get any treatment. Very few of them die. Also, I'm sure someone will give a better answer then this but it might help if you think about the fact that most viruses are spreading well enough, even if they do eventually kill the host. Nil Einne (talk) 09:09, 23 April 2008 (UTC)

(Edit conflict) Only a small number of viruses and bacteria cause their host to die, it's not true to say that any untreated ones do (consider for example the hundreds of millions of people annually infected with the various strains of the common cold, almost none of which die from it). In essence, from a strictly 'selective' viewpoint the infection will cause whatever effect in the host that will maximise it's own survival, or the survival of its genetic material. In some cases this is the death of the host organism, as this may be the best way to rapidly multiply, or this is the way the virus or bacteria assists with its spread to other hosts. There's more to it than that, but other users can expand. --jjron (talk) 09:10, 23 April 2008 (UTC)

(Edit conflict) Actually, most (~99.99999%) viruses and bacteria don't kill the host. When is the last time you heard of someone dying of a cold? The immune system can usually take care of most damaging infections. Generally speaking, it's viruses and bacteria that are poorly adapted to the host that are normally the most dangerous, such as when they jump to a new species. Most viruses and bacteria, over time, usually evolve so that they do not kill the host. However, as with influenza, genes of two similar viruses may get mixed together in one host, producing a new, more dangerous strain. So, a version of flu adapted to only pigs may get mixed together with a version of flu that infects pigs and birds, producing a new version that infects pigs and birds, but is deadly to birds.

Furthermore, many multicellular species have developed symbiotic relationships with bacteria. Mitochondria have even become so symbiotic that most life is dependant on them. Some species even have symbiotic viruses.

Viruses and bacteria have also triggered many mutations in the ancestors of most species by adding some of their genes to other species, some of which were beneficial enough to spread throughout the population. So, the DNA of ancient viruses and bacteria live on in the species you see today in the form of beneficial mutations.

Still, it should be noted that in some cases the death of the host is irrelevant. If the disease manages to spread well enough before the host dies or continues to spread well after the host's death, then the host's death may not harm the bacteria or virus' spread enough to make evolving a less deadly strain occur. A long incubation period may have this effect, giving the host time to join another population, then killing the host during an infectious stage. This is rare though, since it is usually easier to evolve to adapt to the host. -- HiEv 09:17, 23 April 2008 (UTC)

I just have to point out a bit of an error.. The origin of mitochondria (and chloroplasts, in plants) is indeed thought to lie in symbiotic prokaryotes, but it's quite an overstatement to say that most life is dependent on them. Only eukaryotic cells (like our own) host mitochondria, and they represent only a fairly small branch on the tree of life. – ClockworkSoul 12:44, 23 April 2008 (UTC)

Actually, eukaryotes comprise a large branch of the tree of life, including animal, plant, fungi, and protist kingdoms and, with the exception of a few protists, all having mitochondria, while prokaryotes only include bacteria and archaea. I suppose we could discuss the estimated number of total species in each domain, their likely total individual numbers, or their theoretical overall mass on Earth; so let me amend my earlier statement to say "most (if not all) life you visibly encounter" is dependent on mitochondria. -- HiEv 07:09, 24 April 2008 (UTC)

It's important to remember that evolution is not directed (some opinions notwithstanding), so when you see suboptimal traits in nature it's not a matter of "what is the purpose of this feature?" so much as "this feature has not been bad enough to stop this species from surviving". It would be nice if humans could fly and run faster than deer and breathe underwater, but our suboptimal lack of those features has not been enough to do us in. --Sean 12:43, 23 April 2008 (UTC)

Consequences of helium depletion

The world's reserves of helium are being depleted, with US's reserves expected to end within a decade if we keep the extraction rate. What would be the impacts of such depletion on a worldwide scale? It makes me kind of sad to see all these stupid helium balloons around when this resource seems to be almost gone. — Kieff | Talk 10:33, 23 April 2008 (UTC)

Well, note that the economics of it should kick in when the amount left starts to actually be very low (that is, the price will rise so that it becomes worthwhile to conserve it). --Captain Ref Desk (talk) 14:42, 23 April 2008 (UTC)

If it ever becomes viable and implemented on a large scale Fusion power may provide more Helium than we know what to do with. Mad031683 (talk) 17:03, 23 April 2008 (UTC)

I seem to have grossly overestimeted the amount of helium produced in these reactors, since it seems only a few grams of fuel are used in these at a time. Mad031683 (talk) 17:30, 23 April 2008 (UTC)

It may help to consider the magnitude of what we're talking about. For example from helium:

Helium is commercially available in either liquid or gaseous form. As a liquid, it can be supplied in small containers called dewars which hold up to 1,000 liters of helium, or in large ISO containers which have nominal capacities as large as 11,000 gallons (41,637 liters). In gaseous form, small quantities of helium are supplied in high pressure cylinders holding up to 300 standard cubic feet, while large quantities of high pressure gas are supplied in tube trailers which have capacities of up to 180,000 standard cubic feet.

A new plant in Arzew, Algeria producing 600 million cubic feet (1.7×107 m³) came on stream, with enough production to cover all of Europe's demand

For example, the Saturn V booster used in the Apollo program needed about 13 million cubic feet (370,000 m³) of helium to launch.[2]

Also [2] "The Kennedy Space Center alone uses more than 75 million cubic feet annually." (not clear how much of this, is recovered).

According to [3] we currently produce about 25k tonnes of CO2 from power plants and we would produce about 10 million less of helium (it's not clear if we're talking about weight or volume but presume weight since that's what they gave). Even if this figure is inaccurate and it's only 10000 less and allowing for a 40 fold increase in our production from power plants, thats only 100 tonnes of helium per year (at room temperature and ATM). With the Kennedy Space Center using ~380 tonnes per year, that's only 1/4 of their annual usage Nil Einne (talk) 19:52, 28 April 2008 (UTC)

IIRC, the helium reserve was established when the military uses of blimps had a greater impact than is current, and we didn't want to be at the mercy of foreign governments. Gzuckier (talk) 18:28, 23 April 2008 (UTC)

I think the OP was refering to the sources of helium being depleted, not the stockpile of helium that was already extracted. Mad031683 (talk) 18:45, 23 April 2008 (UTC)

Most places that use a lot (or any)liquid helium have return lines to capture the boil off so it can be reused, this will become more important as it becomes more expensive. You may see some people turn to hydrogen instead.--Shniken1 (talk) 02:08, 24 April 2008 (UTC)

Reduced lung capacity and enlarged toncils symptoms

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

As per the guidelines you ignored at the top of this page, we cannot and will not help you with medical, legal or other professional advice. Go see your doctor. -mattbuck (Talk) 14:44, 23 April 2008 (UTC)

ir absorbtion, polar vs nonpolar molecules, methane?

ok; i see that infrared absorbance requires a dipole in the molecule to interact with the electric field, so that N2 or O2 is transparent, but CO2 or H2O isn't. But, recalling that the CH bond is nonpolar, how does CH4 count as a dipole and therefore IR absorber (and therefore greenhouse gas as we all know, but that's not what I'm interested in, just where is the dipole in the CH bond)? Gzuckier (talk) 18:34, 23 April 2008 (UTC)

Perhaps I am misunderstanding something here, but there are no C-H bonds in CO2 or H20. However, the C-O bonds in CO2 are highly polar, and the O-H bonds in H20 are somewhat polar, and therefore CO2 and H20 interact with infrared wavelength radiation. --Bmk (talk) 20:56, 23 April 2008 (UTC)

C-H bonds are not "non-polar" either--the atoms do have different electronegativity--they're just much less polar than C=O, O-H, etc. Minor nit, Bmk: The O-H bonds in the "H2O" water molecule aren't usually considered "hydrogen bonds". That term is more appropriate for the interaction between the H on one water molecule and a different oxygen atom than the one to which it's normally bonded. DMacks (talk) 21:06, 23 April 2008 (UTC)

Yeah C-H bonds are polar, as are all bonds between different elements. You may be confused because Methane and other hydrocarbons are non-polar molecules, this is because the polarity of the bonds are balanced out due to symmetry. CO2 is a non-polar molecule as well.--Shniken1 (talk) 02:03, 24 April 2008 (UTC)

Good point DMacks - i've deleted the misleading link to reflect that. Thanks! --Bmk (talk) 03:04, 24 April 2008 (UTC)

thanks to all, answers my curiosity perfectly.Gzuckier (talk) 14:20, 24 April 2008 (UTC)

Cellphones: signal strength

I've read somewhere that the poorer signal strength a cellphone receives, the stronger signal it transmits. Now, I live in such a place that my phone shows "Network search" most of the time. (Except when I'm at school.) Does it mean it is dangerous to carry the phone around, when there's no signal? --grawity 19:24, 23 April 2008 (UTC)

Dangerous? No one really knows for sure yet, see Mobile phone radiation and health. But yes, cellphones will emit more transmitted power as necessary to reach the cell site; the cell site actually commands the changes in power as needed. In the old analog AMPS days, hand-held cell phones topped out at 600 mW of power (and "bag phones" and car phones topped out at 3W); I don't know if the 600 mW limit is still true in the digital age. (The safety article I mentioned says 2.0W peak for a GSM handset, but "peak power" probably isn't comparable to AMPS power (which was continuous)).

Atlant (talk) 20:45, 23 April 2008 (UTC)

The phone isn't going to keep ramping up the signal indefinitely, and they max out well before they get to anything that modern science considers dangerous. (Microwaves appear to be pretty harmless, except in really high doses.) Can you imagine a situation where a consumer phone might be allowed to transmit dangerous amounts of anything, but only to people not living in cities?

That's not to say that modern science mightn't be wrong. There's still a lot of research being done on the topic. While, it's pretty clear they don't cause cancer, but there are still all sorts of other horrible things that scientists are still studying in relation to phones. However, there's no way the Reference Desk is going to give you an answer that's more correct than current scientific consensus, so we really can't theorize much beyond that. APL (talk) 05:36, 24 April 2008 (UTC)

It's not necessarily more dangerous, but it will certainly drain your battery a lot faster! -- Kesh (talk) 22:33, 24 April 2008 (UTC)