Wikipedia:Reference desk/Archives/Science/2009 October 11

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October 11

Does ether and methanol form an azeotrope?

An experiment procedure effectively adds methanol to ether (that's dissolved my product) and then apparently if I let it boil for a short while before adding water to induce precipitation, most of the ether has evaporated. This is over steam bath -- I know ether boils quick, but this is at least 15 mL ether we're talking about here. How much would methanol depress the boiling point of the mixture, if they form a positive azeotrope?

Theoretically my worry actually is because I'm not sure if I'm dealing with a 2-solvent recrystallization or a 3-solvent recrystallization ... John Riemann Soong (talk) 01:54, 11 October 2009 (UTC)

You could do a quick GC run. The retention times of both methanol and ether should be pretty standard, you could tell roughly how much of your solvent is either methanol or ether based on the chromatography. I am pretty sure you can get rough quantitative assements from a GC run by integrating the area under the peaks. --Jayron32 04:40, 11 October 2009 (UTC)

Unfortunately I have no time to go back to the lab before my report is due (well mainly cuz I have like 2 exams before it). I'm not privileged enough to get a key to a room with a GC unsupervised. John Riemann Soong (talk) 06:18, 11 October 2009 (UTC)

Electroplating Copper on Iron

Hello. Given copper(II) sulfate solution, aluminum, an aluminum salt solution, and iron; I'd like to electroplate copper on iron via a spontaneous redox reaction. I plan to submerge Al in a beaker filled with aluminum nitrate solution and Fe in another filled with CuSO_4(aq). Would Fe react with its electrolyte due to the reactivity series? If so, how can I electroplate Cu on Fe since most Cu salt solutions would react with Fe? Thanks in advance. --Mayfare (talk) 03:14, 11 October 2009 (UTC)

Unfortunately, Iron may be a bad choice for your cathode here since it will react SO readily with the copper, that it may be hard to not get the iron to dissolve off into the solution while you are trying to plate it with the copper. Stainless steel, being a less reactive alloy, may work better, but pure iron is a fairly reactive metal. Drop an ungalvanized iron nail into a copper (II) solution, and within minutes the nail will start to pit and the copper will begin to plate in the pits. This is a sort of "chemiplating", but it will not give a nice, even finish like true electroplating would. --Jayron32 04:29, 11 October 2009 (UTC)

Curious, how do alloys work during electroplating? Surely some sort of phase transition must take place? John Riemann Soong (talk) 06:12, 11 October 2009 (UTC)

Any conductive material can be electroplated. The cathode will gather metal to it regardless of its identity, so ideally you want a conductive, but relatively non-reactive cathode to prevent the material from degrading by doing its own spontaneous redox reactions. Stainless steel would still react with copper (II) solutions, but likely much more slowly than would pure iron, so you would get a fighting chance to electroplate a smooth clean layer of copper onto the surface of the steel. Once the first layer of copper is there, it will protect the underlying metal, so it can build up on its own. --Jayron32 06:12, 12 October 2009 (UTC)

dc motor

diff. b/w wdgAnkit Badnara (talk) 03:50, 11 October 2009 (UTC)

WTF ? StuRat (talk) 15:35, 13 October 2009 (UTC)

Huh? --Jayron32 04:21, 11 October 2009 (UTC)

There's an article on DC motor. I take "b/w" to mean "between". "wdg"??? →Baseball Bugs ^{What's up, Doc?} carrots 04:25, 11 October 2009 (UTC)

b/w could also mean backed with, a common abbreviation back in the days of 45 rpm phonograph singles, like "Hey Jude", b/w "Revolution (song)", indicating the "A-side" and "B-side" of the single. This could be a question for the Entertainment Desk for all we know. --Jayron32 04:35, 11 October 2009 (UTC)

I think we're going to need a complete sentence - at a minimum - if we're going to have a shot at answering something. wgd might be "windings" - so maybe this is something like "What is the voltage difference between the windings of a DC Motor?"...but then it could equally be "Are there diffeomorphisms between wedgies?". SteveBaker (talk) 04:31, 11 October 2009 (UTC)

...or "What is the difference between the windings of the various kinds of DC motors (brushed vs. brushless)?", or "What is the difference between the windings of a DC motor and an AC motor?" Red Act (talk) 05:16, 11 October 2009 (UTC)

If it weren't for the title, it could be a sociological question as to whether interracial marriage can be challenging: "Difficult black/white wedding?" Red Act (talk) 07:16, 12 October 2009 (UTC)

No, the title is easy: dc is mostly black, and I would guess that speakers of motor were probably white. Olaf Davis (talk) 21:49, 13 October 2009 (UTC)

Crack on the Moon

Is there a significant crack on the Moon that dates back about 1400 years? And what's the story behind this?--Email4mobile (talk) 09:23, 11 October 2009 (UTC)

The moon has been thought to be geologically dead for the past few billion years (other than impact cratering), so as far as we know, no. Also, there is no way for us to date to 1400 years ago, and no way for us to get accurate pre-telescope records of fine-scale features. There is an article on Rilles here on wiki, unfortunately I am not a planetary scientist so I can't give you any more info than that ('tis also well past my bedtime). Awickert (talk) 09:30, 11 October 2009 (UTC)

In addition to possible cracks caused by impact craters, there are also moonquakes caused by the Earth-generated tides on the Moon (yes, solid rock experiences tides, too). If we go back much further than 1400 years, there may also be thermal expansion cracks from when the Moon cooled to it's current temp. StuRat (talk) 15:33, 13 October 2009 (UTC)

If by "significant crack" you mean one that is consistent with the widespread claim in Islam that the Prophet split the Moon in two to convince the Unbelievers (Koran 54:1 - well actually, the Koran does not precisely support this myth either, but read it for yourself) then absolutely and emphatically no there is not. The picture you have linked to is a former NASA picture of the day and depicts the Ariadaeus Rille. The NASA article on this rille says that it is relatively young, but planetologists usually mean a lot older than 1400 years by that phrase. It is 300 km long, but that is nowhere near long enough to represent a repaired bisection of the moon. It consists of a line of sunken surface called a graben caused by a parallel line of geological faults. This is nowhere near a traumatic enough process to be connected with moon-splitting. In fact, there are a large number of such rilles (so called straight rilles) all over the surface of the moon going every which way. NASA has an informative article on them. You will need more than a line on the moon to convince this unbeliever. SpinningSpark 16:56, 11 October 2009 (UTC)

We know significantly more about the geology of the Hadley Rille, because Apollo 15 landed there with intent to study it. The best understanding of lunar seismology is still pretty vague - most lunar scientists believe that these faults are cooling-artifacts. They presumably form after thermal expansion of large areas molten lunar crust - areas of lunar surface that melted in cataclysmic impacts (as opposed to the earth-like plate tectonics). However, we can't say for sure since we have very limited data on the moon's subsurface geology. Nimur (talk) 19:32, 11 October 2009 (UTC)

Voice

Does the male voice continue to deepen with age, after puberty? Younger males, around 18 and 19, on average seem to have more high pitched voices compared to older males. Clover345 (talk) 12:08, 11 October 2009 (UTC)

Good question. I thought the answer would be in Vocal register but I can't find it there. Anyway you're right to some extent. Mens voices can deepen till their mid twenties. When men and women get old though mens voices rise again and womens lower so for very old people you might find it difficult to tell from the voice if they're male or female. Dmcq (talk) 13:57, 11 October 2009 (UTC)

Your observations seem to be right. This article contains a helpful diagram of changes in the voice with age, which appears to show the fundamental frequency of the average male voice deepening quickly in the teeage years, then continuing to deepen more slowly until around 40, after which it is relatively stable until it starts rising again at around 60. Karenjc 16:24, 11 October 2009 (UTC)

As with many male/female differences, development of the vocal cords appears to be regulated by hormones. There is a fairly detailed discussion in Vocal folds#Impact of hormones. --- Medical geneticist (talk) 00:10, 12 October 2009 (UTC)

how does double-stranded RNA work?

Nothing I search online seems to address the idea that the ribose sugar is too big and Watson and Crick's original prediction about how RNA couldn't be double-stranded. John Riemann Soong (talk) 15:51, 11 October 2009 (UTC)

Alexander Rich (MIT), one of the discoverers of the structure of dsRNA around 1960, had this to say about the differences between dsRNA and dsDNA:

Eventually, it was discovered that the double-stranded (ds)RNA molecule adopted a conformation similar to the A form of DNA, exclusively using a C3' endo sugar pucker (Fig. 1). The reason for this adherence to the C3' endo sugar pucker in RNA becomes apparent on looking at the position of the additional oxygen that would be present at the C2' position of ribose (See Fig. 1). In the C3' endo conformation of dsRNA, there is adequate separation between the oxygen on C2' and the oxygen on C3' in contrast to a van der Waals crowding that occurs if the dsRNA sugar pucker were C2' endo. Because of the unfavorable energetic situation of ribose in the C2' endo conformation, RNA molecules are usually found in the C3' endo conformation. There is an energy barrier between the two puckers for ribose; in contrast, the deoxyribose ring has very little barrier.

— Alexander Rich, RNA Towards Medicine, doi:10.1007/3-540-27262-3_1, ISBN 978-3-540-27262-5

There may be more recent and detailed commentaries, but I think this addresses the spirit of your question. -- Scray (talk) 19:02, 11 October 2009 (UTC)

decline in platelets

last month i suffered a brain haemorrhage. past 6 days my platelets are on a downward trend;reduced from 298k to 191k. is there a cause to worry? —Preceding unsigned comment added by Nipun310 (talk • contribs) 18:08, 11 October 2009 (UTC)

Sorry, best wishes but we are forbidden to answer questions about people's personal medical conditions. Looie496 (talk) 18:16, 11 October 2009 (UTC)

Here is the guideline that prohibits us from giving medical advice. Please ask your doctor. Red Act (talk) 18:31, 11 October 2009 (UTC)

We can't try to explain what is happening in your situation or whether or not you should worry about it, since that would require detailed knowledge of your situation and it would be inappropriate for us to try to make a diagnosis over the internet. However, we have articles on platelets and hemostasis. A detailed explanation of your particular situation is best left to your doctor. --- Medical geneticist (talk) 00:28, 12 October 2009 (UTC)

paralysed from the waist down

does the wedding tackle still work or not, or does it depend? —Preceding unsigned comment added by 86.128.191.115 (talk) 20:53, 11 October 2009 (UTC)

See Paraplegia#Disability -- Finlay McWalter • Talk 20:55, 11 October 2009 (UTC)

Fixed your link. --Anon, 22:02 UTC, October 11, 2009.

It didn't work for Lord Chatterley. Cuddlyable3 (talk) 13:19, 15 October 2009 (UTC)