Talk:Mole (unit)/Archive 1

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Contents

Etymology

why is it called a mole??—Preceding unsigned comment added by [[User:{{{1}}}|{{{1}}}]] ([[User talk:{{{1}}}|talk]] • [[Special:Contributions/{{{1}}}|contribs]])

Particle

I thought I'd link the "particle" to a relevant article but I could only find particle which is generic, particle physics which isn't very relevant, and subatomic particle which at first seemed to fit but turns out not to after all. The current text is using "particle" in a sense that seems to be narrow and technical but explicitly includes atoms and molecules. Is the term just being used generically to mean something like "small speck," or is there a more precise definition for "particle" when used in this chemical sense? 24.80.122.19 06:41, 14 Apr 2004 (UTC)

Particle is a general statement in Chemistry. You use it in explanations when what you're referring to are atoms or molecules and whatnot. This is because both the terms atom and molecule are themselves specific. An atom is one individual atom (eg. Mg or Na just there by themself) and a molecule refers to a substance that contains several atoms in it, eg. Glucose (C6H12O6).

So when you're talking about the mole you use the term particle in the explanation because moles are applicable to more than one thing.

Yes, congratulations, you have finally ascertained why it's a dimensionless quantity. You get a ph.d.

Half a mole?

The mole makes it easier to interpret chemical equations in practical terms. Thus the equation:

   2H2 + O2 = 2H2O

can be understood as "two moles of hydrogen plus one mole of oxygen yields two moles of water."

2H2, that wouldn't be 4 moles of Hydrogen atoms?

No, because "hydrogen" is referring to hydrogen gas, which is H2, not atomic hydrogen. There are some logical reasons to avoid using half-moles (specifically, the reaction H2 + 1/2O2 implies that two hydrogen atoms interact with an oxygen atom, which of course doesn't happen), but they are often useful. Ckerr 18:49, 22 July 2006 (UTC)


From my knowledge (I'm still in High School chemistry though) it is incorrect use a value of 3.5 (or anything but a whole number) when dealing with the coeffecients in a chemical formula. Did my teacher just explain it this way to simplify it?

It isn't incorrect. I'm used to see formulas like H2 + 1/2O2 -> H2O. But neither is it very common.

I'm in the same situation as you, I am being taught "NO DECIMALS!!!! WHOLE NUMBERS ONLY!!!!!" But I think that for theoretical formulas that aren't telling you what chemicals to add, it's okay, because if you're trying to explain the properties of element X, it would be easier to understand "X + .5O + .33H + .2C--> [random compound]" rather than doing "30X + 15O + 10H + 6C--> 30[random compound]" which is the closest whole-number form of the first equation. Twilight Realm 03:34, 11 October 2005 (UTC)
There is a such thing as half of a mole, or basically any part of a mole. The only reason that teachers discourage the use of fractions of moles is that they also apply the same equations you will be using at the atomic scale, where you have the number of atoms listed in the equations. Its possible to have 0.5 a mole of oxygen atoms in an equation, but impossible to have half of an oxygen atom in an equation, so teachers discourage the use of part moles for the ability to discuss more topics easier with the class. Zack 01:43, 24 January 2006
Fractional mole values may be avoided for pedagogical purposes, but mole fractions are used all the time (in fact unavoidable) in the field of chemical engineering. --Blainster 21:26, 24 January 2006 (UTC)
The material balance equations are usually written in terms of the key component that is being considered. If you are most conserned with the hydrogen, then the oxygen will be 0.5 in quantity. Ifyou are most concerned with the oxygen, then the hydrogen and water will be 2 in quantity. - BeastRHIT 06:25, 9 July 2006 (UTC)

.012 kg?

Why does the article use the term ".012 kg"? Wouldn't it be more logical to state that as "12 g"? Nik42 08:54, 26 Jan 2005 (UTC)

  • Probably because the author wants to express this quantity in another SI base unit, the kilogram, rather than a derived unit like the gram. –Peter J. Acklam 07:13, 7 Feb 2005 (UTC)
    • Ah, right, one of the oddities of the metric system ... the prefix-less form is derived from the prefixed form ... :-) Nik42 04:46, 9 Feb 2005 (UTC)
      • Regardless of what the author might have wanted I agree that it would still be more logical to state it as 12 grams. Easier to read too. I'm changing it. Jimp 30Sep05
"The author" was the CGPM, which used that terminology in its semiofficial English version of resolution officialy defining the unit, and in the offical French version too with French spelling of unit and comma decimal point. It is followed by the BIPM in its SI brochure, and by NIST in SP 811. Well, all of them, as this article did too, actually use the leading zero before the decimal fraction. Nonetheless, I agree that it should be "12 grams". Gene Nygaard 08:49, 30 September 2005 (UTC)

Examples

Wikipedia is better than a normal encyclopedia for many reasons. One of them is that it is easy to understand for the normal person (as it is written and/or edited by normal people). Let's help keep it comprehensible. Avogadro's number, the number which the whole concept of the mole is based upon, is big. Really really big. Enormously big. Way too big to actually comprehend. But we can get an idea of it with some good examples, which also make the article a bit more interesting. 1023, like I said, is unbeleviably huge, but if you don't already know about it, it's just a couple of numbers.

Anyway, my chemistry textbook has two examples to help comprehend the size of the number. The first one is that if you took a mole of sand, it would cover the city of Los Angeles (or something) in 600 meters of sand. The second example is that if you had a mole of rice, it would weigh as much as a million cars for every person on earth. Now, when you read these, you are probabably amazed by how much that is, but you don't get any farther than that. You don't actually get a grasp on how big it is, just that it's really really big. A million cars for every person on earth? No idea how much that is. If, however, you modified the first example, it would work. Get a picture of a single grain of sand among many, show how small it is. Then, get a picture of the city of Los Angeles or whatever it is, an aerial view, and show how much 600 meters would be. That would help a lot.

I'm willing to help, in fact I'll put together the picture, if people agree with me, and if someone can do the calculations to verify the facts (I may have remembered the specifics wrong). Twilight Realm 03:19, 11 October 2005 (UTC)

I haven't done the calculation, but I remember it to the effect of "a mole of sand grains (or maybe rice) would cover Earth a few meters deep." The problem with this is, 'who can actually understand and appreciate the size of Earth?' - BeastRHIT 06:34, 9 July 2006 (UTC)
Avogadro's Number is very big, but it doesn't even come close to googol.--Jack 02:10, 11 October 2006 (UTC)

Then what ARE the units????

Okay, so if mole is not a dimensionless quantity (and I found at least one physics discussion list where it was called such), then what *are* the units? The problem is this: it makes no sense to say you have "one mole of something" you have "one mole of molecules" or "one mole of atoms". Say you have water. Each molecules has 3 atoms. Now, I could say I have "3 moles of water" when I mean "3 moles of atoms of water" or I could say "1 mole of water" when I mean "1 mole of molecules of water. The point is, the unit has no meaning until you specify whether you mean atoms, or molecules, or whatever. That is precisely what a dimensionless quantity is. If it were not, then "1 mole of water" would be "1 mole of water", regardless of whether you picked molecules or atoms. "Amount of substance" is just another way of saying "this many". The fact that you even mentioned the example of "a mole of grains of sand" perfectly illustrates what's going on. So, the units could be not only molecules, or atoms, they could even be grains of sand! In fact, they could be chairs, or windmills, or nations, or ideas. They could be anything at all. This is same thing as realising that "amount of substance" is just a dimensionless quantity which says "take this many of whatever". That is not a unit.

Okay, the example with water isn't the best. The point remains, even if you restrict yourself to so-called "elementary elements", you still get different units depending on what you're measuring. if you measure water, you measure molecules; if you measure hydrogen atoms, you measure atoms. Still, the type of elementary element should remain invariant from measurement to measurement for a "mole" to have any kind of dimensional unit. Otherwise, you end up with nonsense, like

H2 + 0 --> H20

2 moles of hydrogen + one mole of oxygen gives 3 moles of H20. This is what happens when you remain consistent throughout usage (which is what dimensional quantities should do.)

Just to be clear, in every other truly dimensional quantity you think of, when you take 2 of that unit, and add 1 more unit to it, you get 3 of that unit (2 grams + 1 gram = 3 grams; 2 seconds + 1 second = 3 seconds). The mole seems to be the only "dimensional unit" that disobeys that principle: 2 moles (of H) + 1 mole (of O) = 1 mole (of H20). If a mole were a dimensional unit, you'd have 2 + 1 = 3, just like every other one.
Yeah. And it's 2 degrees Celsius outside the house and 18 degrees inside so if I open the windows for theose 2 degrees to come in, it will be 20 degrees here. No, most physical quantities don't add, and that's unrelated to whether they're dimensioned or not. – b_jonas 14:53, 26 March 2006 (UTC)

Portions of physics discussion list

Here are some snippets from a popular physics discussion list, populated with ph.d.'s and working astrophysicists and scientists:

Since mole is not terribly useful in astronomy, we could switch number count for mole. [1]

A mole is dimensionless, but one can still do unit analysis with moles! (same reference)

Yes, thank you Ed Shaya, who works at NASA. You hit the nail on the head -- a mole is dimensionless, yet you can still do unit analysis with it, because it's a number, i.e. 1 mole = 6.02 * 10^23 (TIMES ONE), so when you do dimensional analysis you multiply by

\frac{\mbox{1 mole}}{6.02*10^{23}}

or its inverse. There are no "molecules" or "atoms" running around. If you do try to put them in and do dimensional analysis, you'll get the jibberish I discussed above.

Exhibit B

On the talk page at Mole (ordinary dab page), RitaBijlsma, a working physical chemist, says:

amount of substance does not refer to number of particles. The quantity is perfectly valid without the concept of atoms. The law of multiple proportions and law of definite proportions suffice. It is therefore more elegant to define the mole without refering to number of particles, but as a unit equivalent proportion.

In short, it's more "elegant" to define a mole as dimensionless.

Exhibit C

Mathematica, the premier mathematical computing program, treats a mole as a dimensionless quantity. Here is part of a discussion from the MathGroup Archive:

Hi Chris, as far as I remember, it is CORRECT that Mole is adimensional, saying "a Mole of atoms" is similar to saying "a dozen of atoms", a Mole is a very important number in Chemistry, but you could say "a Mole of cars", or "a Mole of computers", just like you can say "a dozen of computers". The difference is that "dozen" is a useful number in every-day life and "Mole" is a useful number in Chemistry. [2]

Definition?

1 mole is equal to 6.02* 10^23 and the units is entities per mole —The preceding unsigned comment was added by 70.25.179.34 (talk • contribs) 14:23, 25 March 2006 (UTC)

I don't think it is necessary or helpful to say:

"In other words, 1 mole = (# of atoms in 12 grams of carbon 12)/(1 atom), so that a mole is a dimensionless quantity."

The number of atoms in 12 grams of carbon 12 is 6.02 * 10^23, not 6.02 * 10^23 atoms. I think it would be better to simply say:

"In other words, 1 mole = the number of atoms in 12 grams of carbon 12, so that a mole is a dimensionless quantity." —The preceding unsigned comment was added by ArnoldReinhold (talk • contribs) 05:42, 20 October 2005 (UTC)
But the standards-keepers go to great length to make sure that this is not a "dimensionless" quantity. It has dimensions of "amount of substance", and is the base unit for that quantity.
In fact, those standards-keepers are committed to the International System of Units being a "coherent" system of units, at that term is used in metrology jargon. Thus, if this were a merely a dimensionless number, the mole could not possibly be a part of SI.
Contrast, for example, the characterization of "amount of substance" as a base quantity, and the addition of the mole as a base unit in 1971 (see CGPM for chronology), with the recharacterization of the radian and steradian not as a separate class of "supplementary units" but rather as "derived units with special names" in 1995, considered as being multiples of the quantity "one". Note that if these "units based on Avogadro's number" were considered to be pure numbers, they would also be multiples of the "quantity one". Then, since the SI is a "coherent" system, the mole could not be a part of SI at all. Gene Nygaard 22:54, 25 March 2006 (UTC)
I agree with Gene Nygaard. The official definition of the SI by the BIPM is pretty clear on which units are simply "special names for the unit one" such as radian and steradian[3][4] and which are base units of the SI, like moles[5]. The official resolution of the CGPM defining the mole makes it quite clear that it is defined as a unit, not a dimensionless quality.
Additionally I am unconvinced by the arguments that "working astrophysicists" at NASA and "working physical chemists" use the term to mean a dimensionless quality. Statements made on Wikipedia talk pages and non-peer-reviewed mailing lists are not convincing. A statement from an expert in metrology would be more convincing. An official statement from the BIPM, NIST, or other official metrological agency would be very convincing, but that is unlikely to happen as it is contrary to fact (unless the CGPM redefines mole).
Additionally one might choose to use this as evidence in the article that some researchers treat it as a dimensionless quality, but in the SI it is defined as a base unit.--Grouse 12:50, 6 July 2006 (UTC)

unit? isn't just a number?

like saying thousand? you could say "a mole of cats" right? —The preceding unsigned comment was added by 161.76.99.106 (talk • contribs) 00:25, 6 May 2006 (UTC)

That's way too many cats! But, basically yes - it is a specifically defined number or quantity in the metric system. Vsmith 13:06, 6 May 2006 (UTC)

It seems clear...

While to me, as a physicist, it seems sensible to say that the mole is unitless, it is pretty clear that the mole is defined as being dimensionful: "Note that since N(X) is dimensionless, and n(X) has the SI unit mole, the Avogadro constant has the coherent SI unit reciprocal mole." [6] That strikes me as being silly and arbitrary, and the fact that they have to state that the reciprocal mole is coherent implies that one's first thought is to assume it is incoherent. But Wikipedia is not the place to rewrite the definitions of fundamental entities, so I guess the mole really does have units. Ckerr 18:59, 22 July 2006 (UTC)

Moleonaire?

Would someone who had $6.02x10^23 be called a Moleonaire? —The preceding unsigned comment was added by 67.172.248.207 (talk • contribs) 10:43, August 14, 2006 (UTC)

That would be one major counterfeiter --Blainster 20:22, 14 August 2006 (UTC)

Changed my mind...

After some discussions with other, wiser folk at my physics department, I have decided that the mole is best described as a dimensionless unit. It is indisputably a unit--it is defined as one--but the question is whether or not it has dimension. The candidate for being a dimension is "amount of substance", as this is what a mole is defined to measure.

The argument that this is a dimensionless quantity comes from the following: 1. Numbers are dimensionless. 2. Numbers may be used to measure amounts. 3. There is no difference between the use of numbers and moles to measure amounts. Therefore, moles are dimensionless.

Premise (3) is perhaps the most flaky, but I think it can be justified as follows. If I say I have 12.044*10^23 hydrogen atoms, this is identical to the statement that I have 2 moles of hydrogen atoms. The first quantity is clearly dimensionless, since I am using only a number. Since the two statements are identical, the dimensions of the second statement must be identical to the first--and hence, the second statement is dimensionless.

Put another way, by inserting the term "moles", I do not change the dimensions of my statement, only its magnitude: the difference between "2 hydrogen atoms" and "2 moles of hydrogen atoms" is a numerical factor. By contrast, the difference between "2 hydrogen atoms" and "2 kilograms of hydrogen atoms" is a numerical factor and a dimensionful conversion factor (number of hydrogen atoms per kilogram).

Ckerr 14:56, 1 September 2006 (UTC)

Wikipedia is not a place for original research. This is official Wikipedia policy. If you wish to change the page, please provide a citation to an official statement of BIPM or CGPM or a peer-reviewed article in metrology. It is already clear to me by the fact that the official publications of the BIPM include. Also, 2 moles of hydrogen is not exactly equal to 12.044 * 10**23 hydrogen atoms, even if you were to provide more precision. Avogadro's number is an empirical determination of the number of atoms in a mole of substance. A mole is different from mere counting. Grouse 15:24, 1 September 2006 (UTC)

I am well aware of the Wikipedia policy on no original research. However, I was merely describing the means by which I found a reputable source, and thus I was no more conducting original research than someone who finds a relevant book. (I grant that there is a difference between these cases in that it is much easier to verify the contents of a book than the views of Sydney physicists, but verifiability is a different policy.)
[snip]
Ckerr 16:21, 1 September 2006 (UTC)
Upon reading more articles in Metrologia than I ever thought I would, I still haven't found any that state specifically whether the mole is dimensionless or not. The sources you cite do not explicitly address this question, as they merely confirm that the mole has units (which is not under dispute). The firmest evidence that I have found one way or another is that the mole is not included in lists of other dimensionless quantities, which indeed would tend to indicate that it is dimensioned.
I think that the best resolution is to leave the text mostly how it is, but to include a statement that the mole's dimensionality is not entirely clear. (If you think it is clear, then please find an article which states that it has dimension, as opposed to units and as opposed to it being omitted from discussions of other dimensionless quantities--I was unable to do so.) There are certainly many non-peer-reviewed sources which state that the mole is dimensionless and several arguments that it is dimensionless, and in the absence of an article that actually states it has dimension, I think it is unfair to dismiss these as simply being wrong.
Ckerr 16:50, 1 September 2006 (UTC)
OK, I did some more looking in the SI brochure, and I think this[7] pretty clearly indicates that amount of substance is one of the seven dimensions of the SI. What do you think? Grouse 18:08, 1 September 2006 (UTC)
Yes, that's unambiguous. My only criticism of the article as it stands is the use of the word "specifically" three times in one paragraph, but I think the content is now accurate and verifiable. Thanks for taking the time to find appropriate sources. Ckerr 00:10, 2 September 2006 (UTC)
Sure. Actually I think the article could use a bit of work in general... Grouse 07:29, 2 September 2006 (UTC)

From BIPM itself

I received this response from an e-mail I sent to the BIPM:

The mole is not currently regarded as a count and amount of substance is not considered as a dimensionless quantity, or quantity of dimension 1, mainly because the definition of the mole fixes the molar mass of Carbon 12 and is thus linked to the kilogram. It may be that in a few years the mole be re-defined using a fixed value of the Avogadro number. In such a case, its present link with the kilogram would relax and measuring amount of substance would reduce to a counting.

If the dimensionless mole's coffin was lacking any nails, it is certainly not now. Ckerr 12:26, 4 September 2006 (UTC)

Thanks for your diligence on this. --Grouse 13:07, 4 September 2006 (UTC)

multiples

Please don't remove multiples, for consistency they are in all seven base SI units. —Preceding unsigned comment added by 83.5.62.208 (talk • contribs)
That is not a good reason on its own. If you have a better reason please say so here. For consistency's sake I can also remove it from the other base units. Grouse 15:37, 6 September 2006 (UTC)
My reason for restoring multiples is fact of idiocy of many people for which prefix and unit creates one undividable name. For teach them truth about multiples, please restore multiples in mole. If you don't agree, please remove multiples from all seven base units. Why you are removing multiples specifically from mole, leaving them in other units? Why not better retain multiples in mole and remove them from kilogram - strange base unit with prefix? —Preceding unsigned comment added by 83.5.62.208 (talk • contribs)
I think it would be far better to teach people how to form the units with prefixes. There is already an extensive article about this at SI prefix. Adding a table to every article is just tedious and only serves to make the article longer.
Additionally, if others were to agree to use such boilerplate text, it would be far preferable to use a Wikipedia:Template. Among other things, it allows for a central place to make changes to the format of a common element to a group of pages, and to discuss the desirability of such a template. P.S. To sign a comment, just use four swung dashes like this: ~~~~ Grouse 16:04, 6 September 2006 (UTC)
Why you didn't removed multiples from metre, kelvin and kilogram? —Preceding unsigned comment added by 83.5.62.208 (talk • contribs)
I'm fine with just removing them from the ones I've removed from. You are welcome to remove from other articles if you wish. --Grouse 16:16, 6 September 2006 (UTC)
I've removed them from several of the articles - seemed a bit redundant and not needed. Prefixes should be defined and tabulated on the SI page. Next someone would want to put such a table on all the derived units as well. Vsmith 16:10, 6 September 2006 (UTC)
I made very compact template table with SI prefixes, and putted it using template link in all base units, as Grouse advised me.—Preceding unsigned comment added by 83.5.62.208 (talk • contribs)
No, I said that that is what you should do if others agreed that having this sort of information was desirable. So far no one else seems to think so. Let's just be clear on that. Grouse 17:52, 6 September 2006 (UTC)
As many Wikipedians removed prefixes from nearly all SI base units, I removed some forgotten prefix templates too from remaining base units.—Preceding unsigned comment added by 83.5.62.208 (talk • contribs)