Wikipedia:Reference desk/Archives/Science/2006 October 22

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October 22

Craneflies - how have these really crappy insects continued to survive?

I mean, c'mon - the cranefly has got to be the worst-designed insect in all of creation. It's big, slow, mindless, fragile, has no method of defending itself from predators (despite being big and meaty) and is a terrible flier. Every year when they hatch, everything that eats insects feasts upon them. If God exists, the cranefly was either created on one of his off-days, or was some strange practical joke. If reincarnation is real, the people who've really been bad in this life must come back as craneflies as punishment. Seriously, how has this stupid, pointless, annoying creature managed to avoid extinction? --Kurt Shaped Box 01:39, 22 October 2006 (UTC)

There's many of them. ☢ Ҡi∊ff⌇↯ 02:05, 22 October 2006 (UTC)

"It's big, slow, mindless, fragile," - as oppossed to the...uh....intelligent-minded insects? =) I guess god really does have off-days after all, because i always thought humans were god's "strange practical joke". --`/aksha 02:30, 22 October 2006 (UTC)

Most insects at least try to escape if you go for them. I could walk up to a cranefly and slowly squash it with my finger and it wouldn't even see me coming. --Kurt Shaped Box 02:35, 22 October 2006 (UTC)

Probably insane mating. Lovebugs same thing. But these taste bad. They also more importantly taste bad to birds.X [Mac Davis] (SUPERDESK|Help me improve) 03:32, 22 October 2006 (UTC)

I wonder if the fact that they don't try to escape makes the females easier to mate with? God I feel dirty thinking like that.  freshofftheufoΓΛĿЌ  05:06, 22 October 2006 (UTC)

There are a lot of different techniques an organism can use to survive extinction. High fecundity is one of the more common ones. Not to mention, it is impossible to see these things when they aren't flying (camouflage). They are also of very little nutritional value, and it would be a waste of time for an animal to specialise. They only leave the ground once a year to mate, the rest of the time they are larvae. As long as enough mate to regenerate the population (and that wouldn't take much, I assume one female can make thousands of eggs), they will not become extinct. Simple! :) --liquidGhoul 05:20, 22 October 2006 (UTC)

Add to that a high agility that makes it possible to escape attackers and what do you get? The bloody mosquito. The reason it's not extinct is not for lack of us trying. Rarely has mankind been so united as in its efforts to exterminate mosquitoes. And they still thrive. DirkvdM 09:39, 22 October 2006 (UTC)

(reading the cranefly article) "However, it is very easy to accidentally break off their delicate legs when catching them, even without direct contact. This may help them to evade the birds who pursue them as prey." well, there's (part of) your answer. They sacrifice their own legs to survive. I guess they don't exactly need legs to mate and reproduce... --`/aksha 12:39, 22 October 2006 (UTC)

Meaning of TY1CL1

As an example "TT-P-95 TY1CL1 - PAINT,RUBBER", can someone tell me what "TY1CL1" means please? I see it in the title of numerous products.

Thanks

John

Chest rash?

I understand that this question should be directed to a dermatologist, however I just wanted to get a sense of whether or not that would even be necessary. The below pictured rashes (?) in the middle of my chest appeared about three months ago. There are approximately 25 white circular rashes, the largest about a centimeter in diameter, between my pectoral muscles. They are more defined than the resolution of the picture allows. They are not painful, itchy, nor can I feel them at all. They do not protrude from the skin. Does anyone have any idea what they might be? Cduffner 03:58, 22 October 2006 (UTC)

Have you been tanning? If so, they could be old scars. My various deep scars (from multiple motorcycle accidents, getting shot twice, and stabbed once) do not tan. The surface ones - like scratches and such - do eventually tan over. I have similar circles on the back of my right hand from gravel in one accident that do not protrude, itch, or hurt. When I tan, they stay white while the rest of my hand turns red (note, I tan red, not brown). There are a few spots that I don't remember getting scars and I only see when I tan. I was told about two of my left fingers - burned by an iron when I was a toddler. But, I assume that I had some injury long before my memory kicked in. --Kainaw ^(talk) 04:47, 22 October 2006 (UTC)

Hard to tell from the picture. Could be vitiligo. A dermatologist could tell you. - Nunh-huh 05:24, 22 October 2006 (UTC)

Could it really be vitiligo? It doesn't affect any other area of my skin, however I know my grandfather had it. It couldn't be condyloma lata, could it? I'll try to get a clearer picture. Thanks for everyone's help. User:Cduffner 05:35, 22 October 2006 (UTC)

Vitiligo can be limited to one or a few areas. As for condylomata lata - no. - Nunh-huh 05:48, 22 October 2006 (UTC)

Maybe they're just blemishes that have always been there. Your chest is usually covered by clothes, so you would be less likely to notice them, and very few people examine their own chest closely on a regular basis. I remember the day I discovered the freckles on my shoulders that had been there my entire life. I thought it was specks of dirt! XD

Blemish is no more specific an answer than "spots" although in an advertising context it is always code for acne. Freckles are usually not present at birth and can appear any time throughout childhood. alteripse 13:13, 22 October 2006 (UTC)

Not vitiligo. Might be tinea. alteripse 13:13, 22 October 2006 (UTC)

Maybe some birth mark you haven't noticed until now???BlueLighter 14:15, 22 October 2006 (UTC)

Thanks alot, you've all been a great source of information and help. I figure I better just go and ask a dermatologist to be safe. --Cduffner

THis looks a very fuzzy picture. Its not a still from the Alien autopsy film is it?--Light current 17:57, 22 October 2006 (UTC)

So will you report back to us and award a prize to whichever answer was closest? alteripse 21:47, 22 October 2006 (UTC)

Then let me quickly get my prize-winning entry in: paucibacillary Hansen's disease.  --Lambiam^Talk 22:23, 22 October 2006 (UTC)

UPDATE: Turns out it's a fungal infection. Treatment? Apply medicated dandruff shampoo (i.e. Selsun Blue) on the affected area daily for 2-3 weeks. I probably got it from the pool. Thanks guys. --Cduffner

Told ya. But what amazes me is how you got in to see a dermatologist that fast. What is your secret? alteripse 23:13, 22 October 2006 (UTC)

My secret? Have a father who's a dermatologist. :D --Cduffner

Why on earth didn't you ask him first? Also wonder how Kainaw found himself shot and stabbed? --Username132 (talk) 13:50, 17 December 2006 (UTC)

BONDING IN SOLIDS

Explain the forces between two interacting atoms when they are brought nearer to form a molecule

Start with atom and molecule, they link to other articles that explain things in even greater detail. Weregerbil 07:00, 22 October 2006 (UTC)

There are many types of chemical bonds. See that link for details. StuRat 09:57, 22 October 2006 (UTC)

Molecules are formed by Covalent bonds, you should also take a look at that article. --`/aksha 12:26, 22 October 2006 (UTC)

Software Radio

In software radio,How is it posible to diffrentiate between noise and actual modulated signal???

Unless you have a copy of the message being sent or accutaely know its statistics (same thing really), it is not possible. That is the fundamental problem of communications. If you do have a copy, then no information is being sent! 8-)--Light current 13:39, 22 October 2006 (UTC)

would enough negative charge from other sources such as pions, down quarks etc react with normal matter?

would the negative charge from pions, downquarks etc , if controlled in sufficient amounts have the same effect as the negative charges that repel electrons from each other? and if so would the reaction be more powerfull, so instead of just stopping the other electrons, pushing them violently away? Hopefull

All charged particles obey the same laws of electromagnetism. The force only depends on the charges and the distance between them; no other properties of the particles have any effect on the electric force. That said, pions rarely last more than a microsecond, and down quarks can never be separated from other quarks because of color confinement, so neither can be "controlled in sufficient amounts". —Keenan Pepper 20:26, 22 October 2006 (UTC)

can anything other than particles produce charge enough to repel objects instead of just stopping them or are particles always required, can a photon or electron be charged up with more energy to repel stuff? hopefull

I don't understand what you mean by "repel objects instead of just stopping them". Electrons repel other electrons. —Keenan Pepper 04:48, 23 October 2006 (UTC)

All matter that we know of consists of particles. Photons have no electrical charge and do not repel. Each electron has an unalterable charge of −1. Charge is not a form of energy and is a conserved quantity in all interactions, so it cannot be "produced". Two objects will repel each other if they are both charged and their charges have the same sign. Opposites attract. See Static electricity.  --Lambiam^Talk 09:57, 23 October 2006 (UTC)

What do you mean by particles? Aren't pions and down quarks particles? Isn't the only thing known to exsist that isn't known to be a particle or collection of them gravity? Isn't even that strongly suspected to be a particle? — Daniel 03:50, 29 October 2006 (UTC)

Another EM wind question

How powerfull EM waves are required to project air at the speed and directional focus of this weapon, would it be possible to create an EM version of this weapon http://en.wikipedia.org/wiki/Vortex_ring_gun in the future that doesnt need shells, instead accelterates the air useing EM radiation. not now but perhaps in the future. Been trying to figure this out with other facts, but figured i should just ask directly already. Robin

I'm not an expert, but I think the intensity of the radiation needed to result in a notable acceleration of the air would be such that you get a deadly EM-ray gun. The point is that most of the radiation would just pass through. You'd also need rather large amounts of energy.  --Lambiam^Talk 18:47, 22 October 2006 (UTC)

Affordable Device for Measuring soil water content

Simple and affordable: Is there a simple affordable device for homeowners to use to determine if there is enough water content in the soil. This is for gardening, lawn care, general landscaping. This would work at my home.

more complex but afforable: I have a background in electrical engineering and would like to find/put together an affordable watering system (soil moisture measurement, automatic watering system, feedback loop,etc..). I found some info on Time Domain Reflectometers and have worked with those for another application but suspect that is expensive. Just need some ideas to get started. I tried the cheap (<$50.00) water timers (time of day - battery, amount of time- mechanical) but have not found one that works. This is for a family owned farm. My siblings want a small garden but no one has time to make the 60-90 minute drive to water daily.

Eostdiek

Simple resistive moisture detectors fed to comparators to decide whether to turn water off or on is all thats needed. You could control from a computer-- but whats the point?--Light current 14:31, 22 October 2006 (UTC)

Controlling it from a computer would have some advantages:

• You could turn the water on and off from a remote site, via the internet.

• You could base how much to water not only on current soil moisture levels, but also on the weather forecast. This could either be done with a fully automatic system that reads forecast info or by a human who reads a forecast and sets the amount to water (if any), as appropriate. StuRat 20:31, 22 October 2006 (UTC)

A device called rapid moisture metre is availlable for soil engineering use.The device uses carbide which is mixed with the sample of soil and acetelyne gas is produced.The pressure of the gas is proportional to the amount of water in the sample.The device is easily availlable at soil lab equipment shops.amrahs 17:08, 22 October 2006 (UTC)

If you read the initial question, youll see that what you propose is not suitable becuase the questioner wants remote automatic control that your scheme does not provide.--Light current 17:54, 22 October 2006 (UTC)

IR remote

What exactly would you need to build a simple IR remote control. Like a TV remote, only more simple, just an IR on/off switch. Obviously other than just an IR lamp/receiver set.--71.247.247.67 13:50, 22 October 2006 (UTC)

• Basically, what would I need to make a simple one of these? and a matching receiver of course--71.247.247.67 13:53, 22 October 2006 (UTC)

Try Discover Circuits.[1]. There probably one there. Yes there is! [2] 8-)--Light current 14:21, 22 October 2006 (UTC)

What's this aprox. called again?

$\varepsilon \left[\Psi \right]={\frac {\left\langle \Psi |{\hat {H}}|\Psi \right\rangle }{\left\langle \Psi |\Psi \right\rangle }}$

It had a specific name, but I just can't place it, anyone?--71.247.247.67 14:16, 22 October 2006 (UTC)

• Nevermind, it just came to me, and this after about 20 minutes of playing with <math> markup--71.247.247.67 14:19, 22 October 2006 (UTC)

Aqueous Compounds

I know that when a metal is added to water a base forms, and when a non-metal is added to water an acid forms, but can someone explain to me the steps in which a metal or non-metal combine with water to form an acid or base? thanks

It's been many years since I took chemestry, but I seem to recall water being both a weak acid and a weak base, depending on what is introduced to it. Ah, I was correct: Water (molecule)#Amphoteric nature of water. --Wirbelwindヴィルヴェルヴィント (talk) 20:08, 22 October 2006 (UTC)

First of all, what you said isn't true for all metals and all nonmetals. If you add the metal gold or the nonmetal argon to water, nothing happens. Second of all, even those elements that do react with water do it by different mechanisms. However, there are some general trends. If a metal is reactive enough to displace hydrogen from water, then it does so in a redox reaction and forms the hydroxide. For example, alkali metals react like this: 2M + 2H₂O → 2M⁺ + 2OH⁻ + H₂. Nonmetals are usually more complicated; I think all the halogens undergo disproportionation reactions. —Keenan Pepper 20:18, 22 October 2006 (UTC)

Solar position equations

Every web site I have visited that computes solar position provides a list of the various measurements such as hour angle, declination, azimuth, altitude, etc. The problem is that they all seem to differ even when the exact same time, date, latitude and longitude is entered. I thought that I could resolve this simply by finding the equations from which these values were computed but again there are a variety of equations given to compute each value and non of the results agree with the computations done online. I thought at first the problem might be in conversions from radians to degrees and vise versa but the results are still inacurate or wrong. All I am looking to do is to replace a table of sunsets and sunrizes with an equation or series of equations that compute sunrise and sunset. Is there a web site or article where the equations are given and that will provide consistent and accurate results or am I doomed to using tables instead? Adaptron 20:35, 22 October 2006 (UTC)

I think that the reason the websites differ is because some compute sunrise/sunset according to the middle of the Sun, and some according to its upper edge. It is possible to calculate the Sun's position by yourself (a few months ago, I wrote a program to do it); however, you'll need a lot of equations, and your results will be nowhere near as accurate as the websites'.

I suggest using NASA's HORIZONS system. When it comes to accuracy, you can't beat NASA. The HORIZONS system can provide all kinds of information, including sunrise and sunset times. --Bowlhover 22:15, 22 October 2006 (UTC)

Assuming the output data is accurate I can use it for verification. However what I need to to be able to generate sunset and sunrise from within a computer program versus looking up the times. Accuracy is always important but reasonable accuracy is acceptable. While some web sites have reasonably accurate times the other values that are listed do not agree with other web sites or with the equations I have. There must be a web site somewhere that lists reasonably accurate equations with example data that can be verified unless this is considered to be some sort of secret doings that only a trusted few can be told. Adaptron 22:50, 22 October 2006 (UTC)

Note that the exact time of apparent sunrise would also vary depening on local geography and weather. For example, the Sun will appear to rise far earlier on the top of a mountain than at the bottom of the Grand Canyon. Certain atmospheric conditions will also cause more diffraction of sunlight than others, causing the apparent sunrise to occur a bit earlier. Perhaps some of your calculations are "tweaked" to account for the local phenomena in a particular location ? StuRat 23:57, 22 October 2006 (UTC)

Actually the irony here is that while the web based sunrise and sunset results displayed on the websites are seem accurate and identical it is the other values such as time offset, equation of time, solar hour angle, azimuth and zenith that are not the same. In addition the equations provided by the web sites are not the same and the results for sunset and sunrise are inaccurate and not the same. How can the web site provide accurate times for sunrise and sunset but not accurate results for the other values of for sunrise and sunset from the equations they provide??? A list of equations to computer sunrise and sunset from latitude and longitude (and elevation if necessary) do not seem that far fetched. I would think they would be located all over the web. When you consider all of the other detailed and deep depth coverage of even esoteric topics on the web it just does not seem to make sense that there is no web site that provides an accurate set of equations with examples and other details. I get the feeling that it is a jealously guarded secret. Adaptron 01:59, 23 October 2006 (UTC)

There's no secret. Try sunrise equation. For a very detailed tutorial on how to write a program to calculate the Sun's position, try this. Also, from the same website, this webpage gives a tutorial on how to compute sunrise/sunset times. --Bowlhover 02:49, 23 October 2006 (UTC)

The Earth is not a sphere but more like an ellipsoid. Differences in the model used for approximating the shape, and differences between that model and the actual shape, can make a difference for angles and other relevant quantities. These differences should be quite small, and I don't know if they could possibly account for what you see.  --Lambiam^Talk 10:09, 23 October 2006 (UTC)

Okay what appears to be the problem is that many of these sites want you to purchase their software including the Naval Observatory. Although the prices are not outrageous ($13 - $29.95) it appears that they are using the tactic of only providing incomplete, crude or outright incorrect equations while at the same time providing accurate results on their web sites. Although the equations they are using to generate results may be accurate, detailed and complete the ones they have published on the web site are not. Adaptron 16:01, 23 October 2006 (UTC)

Equilibrium Constant, Kp

I am studying equilibrium constants in my college-level chem class and am having trouble understanding reasons behind the directions of the reaction for the equilibrium. When dealing with gases, if the volume is decreased, the pressure increases and the reaction favors the side of the equation with the smaller number of moles of gas and vice versa. It does make logical sense that if there is less volume the reaction will favor less moles, but I am wondering if there is something more concrete to explain this. I think my teacher said the reason is based on the kinetic molecular theory, but I've consulted my text and another text and I don't see how the kinetic molecular theory can explain this. Can anyone shed some light? Thanks.71.240.47.118 21:06, 22 October 2006 (UTC)MS

In general, these kind of equilbria are determined by entropy considerations, but there's an easy way to talk about this particular case: whichever side of the equation has fewer moles of gas must, on average, be the result of synthesis and not decomposition reactions. Synthesis reactions will happen more frequently when there are more particles per volume, because there are more collisions (more attempts at combination). However, the decomposition reactions are not encouraged by a greater number density (at least, not nearly to the same extent), so when the number density increases it takes more molecules that can decompose to balance the increased number of combination reactions, so the equilibrium shifts. --Tardis 20:07, 24 October 2006 (UTC)

i have great cofusion in Kp n Kc. it has been observed that sometimes Kc is greater than Kp in some of the reactions while in some cases it is lesser than that???????why is that so i want a logical answer

Nails

Why do we have white part close to the bed of our nails? They look like half moons, and I could swear that at some point in my life they seemed more pronounced.. so what are they?

Svetlana Miljkovic 22:11, 22 October 2006 (UTC)

It's called the lunula; our article says only a little about its function. -- Finlay McWalter | Talk 22:17, 22 October 2006 (UTC)

I believe that's where the nail is still growing. After that point, it's just being pushed along. StuRat 23:44, 22 October 2006 (UTC)

If that is so, if you cut your nails flat then leave them to grow without cutting, the ends should take up the shape of the 1/2 moons-- Yes?.--Light current 02:10, 23 October 2006 (UTC)

Sort of. The shape of your nails depends on not only how they grow, but how they are cut and torn, bumped etc. But they do tend to grow in that shape which is why nail clippers are curved, and if you peel your nail off (not the whole thing, just the tip) it will make a curved shape. 74.117.47.205 03:24, 23 October 2006 (UTC)

Ah well, thats funny. I always cut my toe nails in a striaght line. And they continue to grow in a straight line! 8-)--Light current 14:57, 23 October 2006 (UTC)

Just because they are growing across a curved area doesn't mean they are growing at different rates, which is what would be needed to change a straight cut to a curved edge. StuRat 19:30, 23 October 2006 (UTC)

Rainbow

I am trying to help my son with his homework and we are stumped, please help. When you stand with your back to the sun, you see the rainbow with a circular arc. Couls you move off to one sidr and then see the rainbow as a segment of an ellipse rather than a segment of a circle? Defend your answer.

Did you read our article Rainbow? You can't move to one side any more than you can jump over your shadow, even if you take a big leap. Promise you won't attack our answer.  --Lambiam^Talk 22:44, 22 October 2006 (UTC)

In other words, of course you can move to one side from your starting position -- but just as your shadow follows you, so does the rainbow. It keeps its circular shape, which exists because the raindrops that light up with each particular color are the ones that form a specific angle with the sun and your eye. (There is a second angle for each color that also works, but less well, hence the double rainbows when the rainbow is intense enough.) As you move, the position where this happens moves with you.

If you're talking about a natural rainbow in the sky, when you move sideways the movement of the rainbow is usually too small to see. You move sideways 20 feet, the rainbow moves sideways 20 feet, but you're looking at it against a plain sky background or against a background of distant objects and you can't see 20 feet of motion at that distance. So you have the illusion that the rainbow is fixed in place. But try it with a spray of water that you can get close to, like from a fountain, or a garden hose nozzle (held by someone else and set to a fine spray). A lawn sprinkler would also work if it's the kind that makes a continuous fine spray that stays in one place, and still another choice is the spray from a waterfall if you can get close enough to it. Get the sun angle right and you'll easily see a rainbow. Now move and watch the rainbow moving with you.

Even with a natural rainbow you can occasionally see it move with you, if you're watching it from a moving vehicle and you catch it against the right sort of background. For example, I've seen this when driving past a mountain lake where there was a rain shower over the lake and sunlight shining on the rain; the rainbow could be seen moving against the mountains on the far side.

--Anonymous, 05:23 UTC, October 23.

Factual basis in psychology for claims about the power of the imagination

Frequently, we hear talk of how something bad has happened to someone, like a relationship has broken down, or they have lost their job or something, and people say that deep down, the person "wanted it to happen." For example, if someone has low self-esteem, and they get a really great job, they might (allegedly) sabotage themselves, and somehow contrive (subconsciously) to get fired, in spite of making every outward sign of effort. The idea is that the underlying self-image is more powerful than the determination to succeed. Presumably it can also work positively for people with high self-esteem. These kinds of observations are commonplace, but what is the scientific basis for them? Do psychologists believe in this power of the imagination, and do they base this on science, or their general understanding and clinical experience? The Mad Echidna 21:41, 22 October 2006 (UTC)

Coincidentally, there was a study in my home town just recently. It's not exactly like the examples you gave, but it's close. False stereotypes can affect performance: B.C. study. Anchoress 22:33, 22 October 2006 (UTC)

People who believe they're going to fail, no matter what, are more likely to fail, no matter what. The explanation is simple: they have no incentive to improve their performance. People who believe they're going to succeed, no matter what, are more likely to fail, no matter what. The explanation is simple: they have no incentive to improve their performance. (But they are more likely to bluster their way out of the mess they create.) Applying this pop psychology insight as a post-hoc explanation to failing individuals has a problem of unfalsifiability.  --Lambiam^Talk 10:25, 23 October 2006 (UTC)

Is the human brain a chemical machine?

I would like to ask some further questions. Is the human brain a chemical machine? Is thinking the result of chemical processes? 202.168.50.40 21:50, 22 October 2006 (UTC)

That seems a bit of an oversimplification. At the very least it is a combination of electrochemistry and chemistry. Read our article Brain, and check out the role of neurons. Then see also the arguments from various sides in Type physicalism.  --Lambiam^Talk 22:40, 22 October 2006 (UTC)

Francis Crick wrote a book called The Astonishing Hypothesis in which he observed, "a person's mental activities are entirely due to the behavior of nerve cells, glial cells, and the atoms, ions, and molecules that make them up and influence them." --JWSchmidt 22:44, 22 October 2006 (UTC)

This is a question that will seem more and more pointless, the older and more educated you become. The answer of course is "yes and no". The entire human body can be described as a chemical machine, and we learn more details every year. That perspective has yielded enormous understanding of mechanisms of inheritance, function, disease, and even some aspects of behavior and personality. On the other hand, there are many other perspectives about the human mind that also contain truth and wisdom, including some truly valuable insights from religious and artistic perspectives. Another perspective entirely is the interpersonal, the way in which our minds are shaped by our relationships with other people. None of these perspectives can be described well from the "chemical machine" perspective. Intelligent adults recognize that different perspectives are useful for different purposes, and choose the best perspective for a specific purpose. The chemical machine perspective does not tell you what would make your life worth living. alteripse 23:08, 22 October 2006 (UTC)

Reductionist answers can answer some kinds of questions very well, and some kinds of questions very poorly. Regarding the mind as a chemical machine is useful for answering some questions ("What is the physiological cause of happiness?") but not for others ("What is the ultimate cause of happiness? How can I achieve it with the people I love?"). Answering questions in only physiochemical terms is rarely useful for anyone but the physiologist or the chemist. --Fastfission 00:53, 23 October 2006 (UTC)

Obviously yes. How else do you thimk it works?--Light current 02:15, 23 October 2006 (UTC)

Perhaps we should say electro-chemical.--Light current 16:32, 23 October 2006 (UTC)

lens

What type of corrective lenses are in the eyeglasses of a person who is nearsighted?

Convex. The things can't start a fire at all. :( Hyenaste ^(tell) 22:36, 22 October 2006 (UTC)

I think concave, actually. See Lens (optics). A convex lens can be used to focus light to a point, and thus start a fire. A concave lens spreads light out, thus (sans modification) can not be used to start a fire. This error was made in Lord of the flies when the myopic (nearsighted) character Piggy starts a fire with his glasses[3]. --TeaDrinker 23:04, 22 October 2006 (UTC)

Oh of course. I was thinking mirror instead of lens (a convex mirror focuses light, ya?). Hyenaste ^(tell) 00:05, 23 October 2006 (UTC)

No, a concave mirror focuses light. A convex lens also focuses light, but you don't use it in a pair of glasses to treat myopia. You use it to treat hyperopia. --Bowlhover 01:56, 23 October 2006 (UTC)

You should all go see an optician! (if you can) 8-(--Light current 02:03, 23 October 2006 (UTC)

Lab report!

Hello there! I'm a little stumped with my lab report I have to hand in tomorrow. I'm quite stuck on a part where it asks me the molarity of my acid solution. The lab was a titration lab with HCl and NaOH. Currently, I have the volume of my acid solution and base solution. It asks for the molarity. I understand Molarity = Moles / Volume (Liters). How would i be able to find the moles of my acid? I don't remember correctly but is it possible to find moles from liters? --Agester 22:55, 22 October 2006 (UTC)

According to the hydrochloric acid article, the density of HCI is 1.18 g/cm^3. Since you know how many litres of the acid you have, you can use this to find out the mass.

Once you have the mass, you can calculate the number of moles it's equivilent to. One mole of HCI is equal to 36.46 g. --Bowlhover 23:20, 22 October 2006 (UTC)

I'm not sure Bowlhover's answer is correct - the density given is for a 37% solution of HCl, which may not be what you have. I would have thought that, given that the experiment was a titration, the purpose of it was to determine the molarity of your HCl solution by finding out how much was required to neutralise a given volume of NaOH solution of known molarity. What you need to do is to find out the molarity of the NaOH, then check the volume of HCl you'd titrated at the end point, and then using those figures and the equation of the reaction, determine the molarity of your HCl solution. --YFB ¿ 23:31, 22 October 2006 (UTC)

I know if i find the molarity of the acid OR base i could find the molarity of the other. The main problem is that all i have is the volume of BOTH the base and acid.... wait! i think i have an idea! since it's a one to one mole ratio (for neutralization which is what i did in the experiment!) wouldn't my moles be 1? since the formula is written as HCl_(aq) + NaOH_(aq) ---> NaCl_(s) + H₂O_(L) (coefficients are one) therefore my Molarity would be 1 mol / (my volume in L) for my acid / base?? --Agester 23:38, 22 October 2006 (UTC)

You're right that it's a 1-1 mole ratio neutralisation, but if you don't know the molarity of either solution then I can't see how you can find the molarity of one from this experiment (Acid-base titration seems to agree with me). You'll need someone more knowledgeable to help you here... all I have is my 4-years-neglected recollections of A-level Chemistry, I'm afraid. --YFB ¿ 23:47, 22 October 2006 (UTC)

Yes. This lab is killing me because I know so easily Molarity_Acid X Volume_Acid = Molarity_Base X Volume_Base. I could find out the problem of this in 2 minutes if they gave me either moles, or molarity of either acid and / or base! --Agester 00:00, 23 October 2006 (UTC)

The required information may be "hidden". For example, your lab manual might say something like, "The solution you will use for the titration was made by dissolving x grams of solid y in z liters of water. --JWSchmidt 02:44, 23 October 2006 (UTC)

Hmm thanks for the input all! I got it. I found out the molarity of the acid (HCl) was given as .1000 Molars (constant for this experiment). It was confusing because the lab manual said the Normality of the base solution was 5 N. And we don't use normality in our lab we use molarity. In addition, i don't think we used a 5 N basic solution since we diluted our base so heavily. I doubted the manual which is why i came here for help. (if i did use that 5 N i would've been in big trouble.) Thanks for the input everyone! --Agester 01:51, 24 October 2006 (UTC)