Talk:Mole (unit)
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[edit] Mole? Seriously?
The unit mol is not spelled mole, at all, ever, in the history of the world. Wow
- mol is the abbreviation, but the unit is called 'mole'. --71.190.143.208 21:25, 14 October 2007 (UTC)
[edit] Rewrite
I've made some fairly significant modifications to the article, to make it more formal--and, more importantly, more accurate. There was also some minor vandalism removed. Specific points I'd like to make:
- Regarding the dimensionality of the mole, please see the preceding discussion, including the quoted passage, which was from an e-mail by Dr. Claudine Thomas of the BIPM. (While not original research, I concede that this isn't verifiable as it was personal correspondence; however, there are plenty of references to the BIPM website which say the same thing, just not as clearly as the way Dr. Thomas has stated it.) The bottom line is that the mole is not dimensionless, though it may become so if the kilogram is redefined. Hence currently the mole is not simply a unit of counting like the dozen, but it may become so in the future.
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- okay, Ckerr, what do you or Grouse or Dr. Claudine Thomas of the BIPM say is the dimension of quantity of stuff that is measured in moles? in terms of fundamental units what is the dimension of the unit "mole"? or of Advogado's number? what's the dimension of that? r b-j 16:12, 2 November 2006 (UTC)
- In the SI[1], the dimension of mole is amount of substance. Avogadro's number has dimensions reciprocal amount of substance. Grouse 16:55, 2 November 2006 (UTC)
- well, i gathered that from the NIST pages: [2] and [3], but it still begs the question. like luminous intensity which is little more than 1⁄683 watt per steradian or simply an omnidirectional source of 4 π⁄683 watt (both at 5.40 ×1014 Hz what determines luminous intensity for other frequencies is a matter of perceptual data, not physical quantity). so there is no dimensional difference between luminous intensity and power. similarly there is no dimensional difference between NA and "dozen" or 1. it's like saying that measuring angles is not dimensionless because you have units like degrees attached to some expression. the dimension "amount of substance" is bogus and anthropometric, not fundamentally physical. the difference between mole and dozen or the difference between mole and percent (besides the hugh difference in magnitude) is that the dimensionless number represented by 1 "dozen" or 1 "percent" is exactly known and defined whereas the dimensionless number represented by 1 "mole" (that is NA) is not known exactly under the current definition of the kilogram. not knowing the numerical value of a physical quantity precisely does not affect what dimension that physical quantity is. r b-j 17:51, 2 November 2006 (UTC)
- I understand your point. Nonetheless, it is quite clear that both luminous intensity and amount of substance are currently base quantities in the official definition of the SI. Grouse 22:52, 2 November 2006 (UTC)
- Of the seven "base" quantities in the SI, three are unnecessary (the mole, the candela, and the kelvin). There is discussion about how to redo the system of units in a more sensible way--please read some of the references listed on this page and on the article page. Incidentally, you're wrong that amount of substance is just like a dozen, because under the current definition the mole is an empirically determined quantity, not a constant. However, according to Dr Thomas, if the kilogram is redefined, then the mole will cease to be physically significant, and will reduce to dimensionless counting just like the dozen. Ckerr 23:36, 2 November 2006 (UTC)
- i am heartened for most of what you said (that the mole, the candela, and the kelvin are essentially "unnecessary" - not sure exactly what you mean by it, but i think i agree). but a mole is like a dozen with only two differences: the first is obviously the magnitude being that NA is much bigger than 12 and the second is that a dozen is precisely defined whereas NA is not known exactly (being "an empirically determined quantity"). but i have to disagree with you that NA is not a constant. it is most certainly a constant (like other physical constants or what NIST calls "fundamental" physical constants) but we just do not know, from the definition, precisely what that constant is. BTW, i had been in conversation with some NIST physicists about this myself (like Peter Mohr) and i know the issue pretty well. not everyone who works in the field agrees, even at NIST, that the Avogadro number is dimensionful. it just is not defined to a precise dimensionless number because we do not know precisely how many Carbon-12 atoms weigh exactly 12 grams. but that number, imprecise as it is, is physically dimensionless. to repeat, not knowing the numerical value of a physical quantity precisely does not affect what dimension that physical quantity is. "dimension" of a physical quantity is a different property of that physical quantity than the amount of it. if they redefine the kilogram so that NA is a defined number, it will not change the dimension. when they redefined the meter so that c became defined to be exactly 299793458 m/s, it did not change the dimension of the speed of light from L T-1 to something else. it is still a velocity or a speed or length per time. if NA is dimensionless after they redefine the kg (assuming they redefine the kg in that manner, they might instead redefine the kg to fix e or
leaving NA to be not exactly known) then NA is of the same dimension (which is the dimension of 1) before such possible redefinition. r b-j 03:34, 11 November 2006 (UTC)
- Actually, I completely agree with you. Personally, I think it is incredibly stupid to say that the mole has dimension, and define the units of Avogadro's number as mole-1. For better or worse, I didn't come up with the definition, and the BIPM makes it quite clear that they think differently. I misspoke when I said that the Avogadro's constant isn't a constant; you're right, it is. What I meant to say was that it's an emprically measured constant (like the fine structure constant, for instance) rather than a defined constant (like the dozen or the permeability constant). Although I also completely agree with you that changing the definition of a quantity shouldn't change its dimensionality, apparently the folks at BIPM see it differently. Anyway, like you I spoke to some physicists and came to similar conclusions to you, and modified the article accordingly. However, it was correctly pointed out that no matter how many physicists think otherwise, they don't define the units, and if the BIPM says the mole has units, then ipso facto it has units! If you can find some reference, preferably a paper, which says that some physicists consider the mole dimensionless, please put it in. I was, to my surprise, unable to find any such reference. Minor point: by "unnecessary", I mean they can be defined in terms of other constants. Of course, this does not apply to the other four quantities, despite what some of my first-year students think (they sometimes add velocities to masses). Ckerr 09:20, 11 November 2006 (UTC)
- i am heartened for most of what you said (that the mole, the candela, and the kelvin are essentially "unnecessary" - not sure exactly what you mean by it, but i think i agree). but a mole is like a dozen with only two differences: the first is obviously the magnitude being that NA is much bigger than 12 and the second is that a dozen is precisely defined whereas NA is not known exactly (being "an empirically determined quantity"). but i have to disagree with you that NA is not a constant. it is most certainly a constant (like other physical constants or what NIST calls "fundamental" physical constants) but we just do not know, from the definition, precisely what that constant is. BTW, i had been in conversation with some NIST physicists about this myself (like Peter Mohr) and i know the issue pretty well. not everyone who works in the field agrees, even at NIST, that the Avogadro number is dimensionful. it just is not defined to a precise dimensionless number because we do not know precisely how many Carbon-12 atoms weigh exactly 12 grams. but that number, imprecise as it is, is physically dimensionless. to repeat, not knowing the numerical value of a physical quantity precisely does not affect what dimension that physical quantity is. "dimension" of a physical quantity is a different property of that physical quantity than the amount of it. if they redefine the kilogram so that NA is a defined number, it will not change the dimension. when they redefined the meter so that c became defined to be exactly 299793458 m/s, it did not change the dimension of the speed of light from L T-1 to something else. it is still a velocity or a speed or length per time. if NA is dimensionless after they redefine the kg (assuming they redefine the kg in that manner, they might instead redefine the kg to fix e or
- Of the seven "base" quantities in the SI, three are unnecessary (the mole, the candela, and the kelvin). There is discussion about how to redo the system of units in a more sensible way--please read some of the references listed on this page and on the article page. Incidentally, you're wrong that amount of substance is just like a dozen, because under the current definition the mole is an empirically determined quantity, not a constant. However, according to Dr Thomas, if the kilogram is redefined, then the mole will cease to be physically significant, and will reduce to dimensionless counting just like the dozen. Ckerr 23:36, 2 November 2006 (UTC)
- I understand your point. Nonetheless, it is quite clear that both luminous intensity and amount of substance are currently base quantities in the official definition of the SI. Grouse 22:52, 2 November 2006 (UTC)
- well, i gathered that from the NIST pages: [2] and [3], but it still begs the question. like luminous intensity which is little more than 1⁄683 watt per steradian or simply an omnidirectional source of 4 π⁄683 watt (both at 5.40 ×1014 Hz what determines luminous intensity for other frequencies is a matter of perceptual data, not physical quantity). so there is no dimensional difference between luminous intensity and power. similarly there is no dimensional difference between NA and "dozen" or 1. it's like saying that measuring angles is not dimensionless because you have units like degrees attached to some expression. the dimension "amount of substance" is bogus and anthropometric, not fundamentally physical. the difference between mole and dozen or the difference between mole and percent (besides the hugh difference in magnitude) is that the dimensionless number represented by 1 "dozen" or 1 "percent" is exactly known and defined whereas the dimensionless number represented by 1 "mole" (that is NA) is not known exactly under the current definition of the kilogram. not knowing the numerical value of a physical quantity precisely does not affect what dimension that physical quantity is. r b-j 17:51, 2 November 2006 (UTC)
- In the SI[1], the dimension of mole is amount of substance. Avogadro's number has dimensions reciprocal amount of substance. Grouse 16:55, 2 November 2006 (UTC)
- okay, Ckerr, what do you or Grouse or Dr. Claudine Thomas of the BIPM say is the dimension of quantity of stuff that is measured in moles? in terms of fundamental units what is the dimension of the unit "mole"? or of Advogado's number? what's the dimension of that? r b-j 16:12, 2 November 2006 (UTC)
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- I disagree with the above conclusions. There are no "ipso facto" definitions, unless you are writing an article on Mole (SI). Empirically, the term mole can and has been used perfectly successfully without the stupidity of the SI's fiat definition. Many use it without knowing or without regard to that definition and many use it, as noted, with distaste for the unnecessary parts of the SI's definition. I don't mind if the article specifically lays out the SI's definition, as long as it is clear that it is the SI's definition, rather than "the" definition. It makes no sense to say that we must get the approval of measurement experts when the definition in actual use seems to differ from those you'd consider experts, especially when there are no ill effects (unknowledgeable college kids are one thing, this is another).
- Perhaps the strongest argument is that the definition hamstrings the explanatory power of the article because the SI definition is conceptually flawed. I'd like to make it easy for readers to understand why a mole is used, but I can't because of "formality". Formality to get more precise descriptions of reality or to help people get better results from abstract things is one thing. Formality as an end in itself or to give allegiance in thought to a decision that many think was foolish is quite another. 12.210.82.217 08:36, 12 February 2007 (UTC)
- It is Wikipedia policy that information here must be verifiable from reliable sources in the relevant field. You are welcome to provide citations to the metrological literature that support a current use of mole other than the SI one, which has also been adopted by all respected national measurements agencies. Until then, the article should reflect the SI definition of the mole.
- You might also decide that the definition of the meter in terms of "distance travelled by light in absolute vacuum in 1/299,792,458 of a second" is confusing and bears little relation to how most people think about meters. But it is the only current definition that you will find supported by reliable sources. Grouse 10:53, 12 February 2007 (UTC)
- Examples that try to put the size of the mole in everyday terms have been given a separate section. I don't find the "a billion dollars a day for a trillion years" example terribly helpful, since neither a billion dollars nor a trillion years is a comprehensible concept, but I've left it in in case someone else finds it helpful. I encourage anyone to add their own examples, but check their veracity first--for example, the example about the number of human cells was dubious, so I modified it and found a reference.
- Thanks to everyone who has kept an eye out for vandalism; unfortunately it looks like we will have to continue doing so. Ckerr 11:36, 22 October 2006 (UTC)
- Many thanks for this rewrite. Things are much better now. I don't really find the examples helpful personally, since as you point out, they are in terms of things that are not really that comprehensible. Grouse 13:01, 22 October 2006 (UTC)
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- OK, I see now - a letter from Dr. Thomas, hmm... I had removed that bit as it seemed not to be a verifiable published source. Now it's back with a link to a PDF file, OK that's better, however, scanning through the reference you supplied I see no direct support for the sentence (or maybe I'm missing something here). There is no mention of a Dr. Claudine Thomas, the supposed reference that was attached to the line I removed. Nor do I find the phrase physical significance in the PDF file. If it is your or someones else's unpublished speculating and/or interpreting the source, then it counts as original research. If the sentence However, if in the future the kilogram is redefined in terms of a specific number of carbon-12 atoms (see below), then the value of Avogadro's number will be defined rather than measured, and the mole will cease to become a unit of physical significance. is from the file then ok - but please point it out to us. PDF file Cheers, Vsmith 16:39, 30 October 2006 (UTC)
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- The material I was referring to was on page 77, where they propose a definition of the mole and state that "It allows the mole to be redefined in a simpler and more understandable way." There is also this article, which says "[The mole] is convenient to establish the balance in any transmutation reaction between elementary entities, but it is definitely not essential in a base units system because it is redundant with the existing macroscopic mass unit, the kilogram". That article also mentions the current physically-significant definition of the mole (footnote 8), and discusses a fixed Avogadro number alternative. Neither this article (nor the previous one I cited) explicitly states that the redefined mole would be lacking physical significance, but the purpose of an encyclopedia is to provide some synthesis of primary sources, not a collage of short snippets from them. I think the sources make it clear that the "simplification" of the mole's definition would be a result of the removal of its physical significance; if you disagree, I invite you to find a source which says otherwise! Anyway, as I mentioned on your talk page, it's usually more helpful to add a [citation needed] tag instead of deleting material outright, especially if you don't always check the discussion page first. If no citation is forthcoming, then delete away. Ckerr 10:47, 31 October 2006 (UTC)
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[edit] Diagram
I'm not a chemist, but isn't the picture associated with this article ridiculously confusing? Wouldn't it be easier to represent whatever this image shows with text? It looks like it's saying that multiplying the moles by the mass of the constituents gives the mass. Why do we need a crazy abstract art thing to show this? Alex Dodge 06:18, 30 October 2006 (UTC)
- I never really looked at the diagram before, and when I did I couldn't quite make sense of it either. It's nice to have a picture, but I think that one did more harm than good, so I've removed it. Ckerr 10:51, 31 October 2006 (UTC)
- What sort of image would be helpful? Grouse 11:07, 31 October 2006 (UTC)
- Perhaps a photograph of 0.012 kilograms of carbon-12? For comparison, see the metre article and the kilogram article. Alex Dodge 02:05, 3 November 2006 (UTC)
- I actually already tried to look for that, but all the images I found were copywrited. If you can find one, that would be great! Ckerr 07:20, 3 November 2006 (UTC)
- Perhaps a photograph of 0.012 kilograms of carbon-12? For comparison, see the metre article and the kilogram article. Alex Dodge 02:05, 3 November 2006 (UTC)
- What sort of image would be helpful? Grouse 11:07, 31 October 2006 (UTC)
[edit] Definition of "dimension"
I found the ISO International vocabulary of basic and general terms in metrology ([draft third edition http://www.ntmdt.ru/download/vim.pdf]) which defines "quantity dimension, dimension of a quantity, dimension" as:
dependence of a given quantity on the base quantities of a system of quantities, represented by the product of powers of factors corresponding to the base quantities NOTES 1 The conventional symbolic representation of the dimension of a base quantity is a single upper case letter in roman (upright) sans-serif type. The conventional symbolic representation of the dimension of a derived quantity is the product of powers of the dimensions of the base quantities according to the definition of the derived quantity. 2 Quantities having the same dimension are not necessarily quantities of the same kind. 3 In deriving the dimension of a quantity, no account is taken of any numerical factor, nor of its scalar, vector or tensor character. 4 The dimension of a base quantity is generally referred to as ‘base dimension’, and similarly for a ‘derived dimension’.
No mention of things being "fundamentally physical" is included. Grouse 09:15, 3 November 2006 (UTC)
- Indeed. But if the kilogram is redefined, then suggestions are that the mole will cease to be a base unit, and hence the criterion for dimensionality will fail. (Similar arguments may be made for the candela and kelvin, though my guess is that the latter might be around for awhile yet.) Ckerr 15:32, 3 November 2006 (UTC)
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- this is correct. but i still fail to grasp why defining or knowing a quantity exactly can change its dimension. it cannot. Avogadro's number is the dimensionless number that is the number carbon-12 atoms that will weigh the same as 12/1000 of that kilogram prototype in Paris. if the mass of a carbon-12 atom is the same dimension of quantity as the mass of the kg prototype (which it most certainly is), then NA must be dimensionless. r b-j 03:43, 11 November 2006 (UTC)
- i still fail to grasp why defining or knowing a quantity exactly can change its dimension I don't see anything in the definition above about exactly knowing a quantity.
- Avogadro's number is the dimensionless number No, it isn't, and I have already provided sources for this. If you wish to make a contrary assertion please provide a source in the metrological literature for it. Grouse 12:07, 2 December 2006 (UTC)
- this is correct. but i still fail to grasp why defining or knowing a quantity exactly can change its dimension. it cannot. Avogadro's number is the dimensionless number that is the number carbon-12 atoms that will weigh the same as 12/1000 of that kilogram prototype in Paris. if the mass of a carbon-12 atom is the same dimension of quantity as the mass of the kg prototype (which it most certainly is), then NA must be dimensionless. r b-j 03:43, 11 November 2006 (UTC)
[edit] About the wording
this page needs MAJOR REWORDING none of this makes sence and is accurate. 10:17, 8 June 2007 (UTC)
[edit] Physics?
Are moles really more relevant to physics than chemistry? I've always thought of the unit as a basic unit of Chemistry. I've never used it with respect to physics, but very often for chemistry work. 71.190.143.208 21:34, 14 October 2007 (UTC)
- Good point - most physicists wouldn't know a mole if it bit them. Added chemistry template, but left physics there as somebody clearly thought it was important to physics...
