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This article was nominated for deletion on 2005-10-24. The result of the discussion was keep. An archived record of this discussion can be found here.

Message to Ed Cormany

Ed. May I ask your reasons for redirecting _Amount of substance_ to _Mole (unit)_ ? The former is a physical quantity; the latter is a unit for measuring the physical quantity. As such they are very different and, from the physical perspective, we need two different articles. We have this with _Length_ and _Metre_, _Mass_ and _Kilogram_, _Time_ and _Second_, _Temperature_ and _Kelvin_, etc. etc. All of these are Physical Quantities and their respective SI base units. Thanks Ian Cairns 21:19, 7 Jul 2004 (UTC)

Ian, when I created the redirect every piece of information that was present in the amount of substance article was also present in the mole article, sometimes word-for-word. As such, it seemed redundant to me and I redirected it. If you have some additional content to add to amount of substance to make it a better standalone article, please edit over the redirect. Even if you feel that the redirect is inappropriate and should simply be reverted to the previous page edit, go ahead. Be bold in editing pages; that's what I was when I first created the redirect. Ed Cormany 00:38, 8 Jul 2004 (UTC)

Ed, Thanks for that. I'm happy to revert it. The physical quantity and the unit belong to different categories within the same subject area, and it helps to separate the descriptions as much as possible. Some overlap is unavoidable. However, it may well be that there is some redistribution of content possible between the articles, and I'll action this. Ian Cairns 11:14, 8 Jul 2004 (UTC)

Substance or Matter?

Amount rather than quantity

The existence of this article is necessitated by the failure to use the term Avogadro's number as the name of the physical quantity identified by the chemical unit mole (unit), and also by the unfortunate use of the term in NIST and BIPM publications. Using the term "amount" requires the additional explanation that it really means "quantity", and that it does not refer to mass, neither of which would have been required if the the terms "quantity of particles" or "number of particles" had been used instead. --Blainster 17:49, 24 October 2005 (UTC)[reply]

Votes for deletion

Keep. The keepers of our standards insist on making a distinction. This is made clear in both BIPM's SI brochure [1] and in NIST's Guide for the Use of the Internaiotnal System of Units (SI)[2]. Gene Nygaard 19:30, 24 October 2005 (UTC)[reply]

I see that the term "amount of substance" is used in the NIST guide under 8.6.1 here but was unable to readily find it in the BIPM site. Nevertheless, the term itself is ambiguous and thus inaccurate. What the writers intend by using the term "amount of substance" is actually "number of particles", for which the defined quantity would be Avogadro's number. I agree that the distinction you refer to does exist between the number or quantity of particles and the units (mole) used to measure them, and this is retained by using the term Avogadros number instead of amount of substance. As I have noted, it would be acceptable to me to retain the article with a redirect to Avogadro's number. --Blainster 20:08, 24 October 2005 (UTC)[reply]

Delete. Geology has keepers of standards, and their latest classification of metamorphic rocks is, IMO, such nonsense that it isn't worth fixing. The most common errors are the ones here: a dependence upon theory, and the failure of jargon to match common language when possible. This very long article did not clarify how one should specify the amount of a substance. Am I to assume from the article that I must prefer a theory-dependent term, like mole, over the fundamental mass? Many theorems in thermodynamics fail when using the mole fraction of formula units, but work when using the mass fraction of formula units. One should use the most general term that satisfies one's sentence. 'I sent each laboratory the same amount of SMOW (standard mean ocean water)!' is a sentence that uses 'amount of substance' correctly. 'Amount of substance' is not a quantity until three variables are specified. Although each variable can be sometimes chosen arbitrarily, there are occasions when each variable must be uniquely chosen. This should allow the scientist the latitude to choose three variables when specifying an 'amount of substance'. Geologist (talk) 02:08, 29 September 2009 (UTC)[reply]

Symbol n?

Does anyone know where it comes? —Preceding unsigned comment added by 128.214.98.177 (talk) 08:55, 9 September 2008 (UTC)[reply]

This is an excellent question. Researchers tend to adopt the usage in texts, and books on phase equilibrium are the first to be culled by libraries for space. This is occurring before a good history of the subject has been written. Early works always refer to m_i, the mass-fraction of the designated unit of matter i, such as (H₂0)/3 (the gram-atom unit), a choice that allows reaction coefficients to sum to 0, and allows many theorems to easily be written (theorems that fail with mole-fraction). One assumes n followed m. A good history is needed. Geologist (talk) 01:14, 29 September 2009 (UTC)[reply]

"It is possible to measure the ratios of the numbers of entities in chemical samples more precisely than it is possible to count the absolute numbers of entities"

This is true. However, it might be worth letting the reader know that in the everyday work of maybe 99% of chemists and other scientists, this is irrelevant. Avogadro's constant is known to about eight significant figures, whereas typical mass measurements in the lab have no more than six. So in most cases the precision of the calculated number of entities is not limited by our knowledge of Avogadro's constant. (I say this because the section about the "Rationale for preferring amount-of-substance to absolute numbers" provides examples that talk about "chemists", and not about metrologists!) --Itub (talk) 13:22, 15 June 2009 (UTC)[reply]

Let's not forget that the purity of most lab reagents is only three significant figures, which the BIPM puts down as the most usual limitation to the measurement of amount of substance. Physchim62 (talk) 13:32, 15 June 2009 (UTC)[reply]

Motivation for not using Mass Fraction

...Many paragraphs deleted by the writer.

My own very long criticism of this article, an article which has spawned Amount concentration and Amount fraction (which have their own criticisms) has been removed by me. My criticism was a long list of unacceptable conclusions that I believe follow from the article (and still do). My conclusion was that, if the SI recommended it, it should be mentioned; but it need not be adopted. All this was based on this sentence:

The International System of Units (SI) defines the amount of substance to be a base physical quantity that is proportional to the number of elementary entities present.

When I read the original SI document, I found that the amount of substance can instead be defined to be any reasonable unit one wishes to create, not just defined to be in moles. Perhaps this can be clarified.

My own notebooks on thermodynamic studies contain, I discovered, 'amount of substance' written many times by me. The erroneous 'definition', the very long article, and the articles spawned confused me so much that I didn't recognize that I had long ago chosen the same (arbitrary) term 'amount of substance' that the SI chose.

When writing about fundamentals, one must be extremely careful, careful in natural language, in logic, and in mathematics. The SI never defined the amount of substance to be a mole. They simply added a new quantity (new to me, at least) to be used when symbolically writing chemical relations that they propose to be a base dimension (a primary dimension) in Dimensional analysis. This chart tells all:

http://en.wikipedia.org/wiki/Physical_quantity#Base_quantities.2C_derived_quantities_and_dimensions

We already had mass (M) and volume (L³), and substance (N) now extends dimensional analyses to proposed relations among chemical phenomena. To best distinguish amounts of carbon from nitrogen, the SI reasonably chose the number of its moles.

That's it.

One may use amount of substance, mass, & volume to create any secondary dimension or any unit one finds convenient. One need not exclusively use moles (and mole fractions). Some units, such as molarity, ppm, ppb, &c, are invariant in being the quotient of n_i and V. These, for an unknown reason, were described as being the same amount concentration by the SI. I can't imagine using it.

One may wonder why the SI chose a theoretical term, 'mole'. My guess would be that all other expressions for the concept of an amount of a substance contain secondary or derived quantities. The other reason may be that this need not be a theoretical term. The number of grams to choose for the amount of one mole of carbon can be deduced from assigning 1 to H, and using chemistry to complete the periodic table. Atomic theory need not be assumed.

This arbitrary term 'amount of substance', chosen to describe the fundamental quantity 'mole', doesn't really deserve, IMO, this very lengthly exposition that apparently did not clarity a concept that was actually trivial.

Below are responses to my queries about why I could no longer express the amount of Pb by its mass. Physchim62 clearly misunderstood my confusion, and I his. I suggest the article be severely curtailed, and amount concentration & amount fraction either deleted or kept contained within this article. They are being misunderstood elsewhere as replacements for molarity & mole fraction.

The digressions on the ideal gas model, melting-point depression, and osmotic pressure confused me into thinking Physchim62 was explaining why it was convenient to use the theory-laden term 'mole'.

67.91.218.205 (talk) 01:20, 1 October 2009 (UTC)[reply]

The usual version of the ideal gas law is pV = nRT, where n is the amount of substance in the system (as defined in this article). You could rewrite the ideal gas law as pV = NkT, where N is the number of molecules, but you run into a problem: how do you count the number of molecules?

The concept of amount of substance comes about because we can easily find physical relationships which depend on the number of molecules, such as melting-point depression or osmosis, but we don't measure the number of molecules directly, merely a ratio of numbers of molecules in different samples. Electrical measurements are exactly analogous: we know that electric current is a certain number of electrons per second, but we don't know exactly how many. Electric charge at the macroscopic scale is measure in coulombs and not as a multiple of the elementary charge. Amount of substance at the macroscopic scale is measured in moles and not in numbers of molecules. The distinction arises from how we measure these quantities, it is not artificial at all.

I see no reason why Wikipedia should chose to prefer your point of view that amount of substance is an artificial definition over and above the views of the various professional bodies which state otherwise. Physchim62 (talk) 12:01, 29 September 2009 (UTC)[reply]

...Many paragraphs removed by writer.

We are mis-communicating. 67.91.218.205 (talk) 01:20, 1 October 2009 (UTC)[reply]

The power to "carefully decide whether it wishes to follow it" implies the power to carefully decide whether it wishes to ignore it. I shall take the latter route, thank you. Physchim62 (talk) 19:52, 30 September 2009 (UTC)[reply]

@@ Line 44: / Line 44: @@
 == Motivation for not using Mass Fraction ==
+...Many paragraphs deleted by the writer.
-''In thermodynamics, the total number of particles (in absolute terms or in terms of moles) in a system is a basic thermodynamic variable. The difference in the energy of the system as one changes the number of particles by one (while adding or subtracting as much heat, and doing as much positive or negative work, so as to keep the entropy and the volume of the system constant) is a fundamental quantity called the chemical potential. A very standard result into which the number of particles enters directly (and which is taught even at the high school level) is the ideal gas law.''
+My own very long criticism of this article, an article which has spawned [[Amount concentration]] and [[Amount fraction]] (which have their own criticisms) has been removed by me. My criticism was a long list of unacceptable conclusions that I believe follow from the article (and still do). My conclusion was that, if the SI recommended it, it should be mentioned; but it need not be adopted. All this was based on this sentence:
-The elimination of mass as measuring the amount of substance is solely to make certain graphs of mixtures simpler. Thermodynamics traditionally used specific quantities, not molar quantities.
+''The International System of Units (SI) defines the amount of substance to be a base physical quantity that is proportional to the number of elementary entities present.''
-In classical thermodynamics, the mass-fraction of a substance (whose formula-unit is irrelevant) is used. Gibbs's famous paper did not use mole fractions or formula units. The basic thermodynamic variables are volume, entropy, and mass of each chemical component. The chemical potential of a component was the specific chemical potential: partial derivative wrt mass-fraction of that component (irrespective of its formula unit).
+When I read the original SI document, I found that the amount of substance can instead be defined to be any reasonable unit one wishes to create, not just defined to be in moles. Perhaps this can be clarified.
-Reactions can be written without any molecular theory. Symbolically, the coefficients require no decimal points. In fact, one can write m<sub>1</sub> hydrogen + m<sub>2</sub> oxygen = m<sub>3</sub> water, without having to choose an arbitrarily formula unit (H<sub>2</sub>0). When measuring the amount of substance of a phase, as in indifferent theorems or theorems involving open systems, the mass is preferred. I should think biochemists would prefer not having to choose a formula unit.
+My own notebooks on thermodynamic studies contain, I discovered, 'amount of substance' written many times by me. The erroneous 'definition', the very long article, and the articles spawned confused me so much that I didn't recognize that I had long ago chosen the same (arbitrary) term 'amount of substance' that the SI chose.
-(One can satisfy both simple reaction coefficients and the conservation of mass by choosing mass-atomic formula units: divide each arbitrary formula unit by the sum of its atoms. You will now find the reaction coefficients sum to zero. These reactions satisfy indifferent theorems, as the balancing of masses does.)
+When writing about fundamentals, one must be extremely careful, careful in natural language, in logic, and in mathematics. The SI never defined the amount of substance to be a mole. They simply added a new quantity (new to me, at least) to be used when symbolically writing chemical relations that they propose to be a base dimension (a primary dimension) in [[Dimensional analysis]]. This chart tells all:
-Salts or minerals can be written in any (homogeneous) formula unit. Phase diagrams drawn with mass fractions as abscissa all look the same, despite one's choice of formula unit. The diagram of an ideal mixture, however, will not appear symmetrical. This is not an advantage when the solution occupies only part of the diagram.
+http://en.wikipedia.org/wiki/Physical_quantity#Base_quantities.2C_derived_quantities_and_dimensions
-In short, the definition of 'amount of substance' is solely to imitate the simplicity of mass and preserve integral reaction coefficients and symmetrical mixtures. It is an artificial definition, convenient to the organic chemist. Any scientist, however, should see it does nothing but arbitrarily inhibit one's view & language; and it should not be used.
+We already had mass (M) and volume (L<sup>3</sup>), and substance (N) now extends dimensional analyses to proposed relations among chemical phenomena. To best distinguish amounts of carbon from nitrogen, the SI reasonably chose the number of its moles.
-The Wikipedia may choose to state that some organizations restrict 'amount of substance' in this way; but there is no reason why the Wikipedia needs to adopt and propagate this terminology throughout its encyclopedia. It is, IMO, rather silly, bad science. [[User:Bruce Bathurst|Geologist]] ([[User talk:Bruce Bathurst|talk]]) 05:59, 29 September 2009 (UTC)
-:The usual version of the [[ideal gas law]] is ''pV''&nbsp;=&nbsp;''nRT'', where ''n'' is the amount of substance in the system (as defined in this article). You could rewrite the ideal gas law as ''pV''&nbsp;=&nbsp;''NkT'', where ''N'' is the number of molecules, but you run into a problem: how do you count the number of molecules?
-:The concept of amount of substance comes about because we can easily find physical relationships which depend on the number of molecules, such as [[melting-point depression]] or [[osmosis]], but we don't measure the number of molecules directly, merely a ratio of numbers of molecules in different samples. Electrical measurements are exactly analogous: we know that electric current is a certain number of electrons per second, but we don't know exactly how many. Electric charge at the macroscopic scale is measure in coulombs and not as a multiple of the elementary charge. Amount of substance at the macroscopic scale is measured in moles and not in numbers of molecules. The distinction arises from ''how we measure'' these quantities, it is not artificial at all.
-:I see no reason why Wikipedia should chose to prefer your point of view that amount of substance is an artificial definition over and above the views of the various professional bodies which state otherwise. [[User:Physchim62|Physchim62]] [[User talk:Physchim62|(talk)]] 12:01, 29 September 2009 (UTC)
+That's it.
-[START NOTE: This is being written after that below. Upon examining [[SI base unit]], I read that 'amount of substance' is just a description of the base unit 'mole'. This sounds perfectly satisfactory. I haven't the SI document. Does it warrant 'defining' 'amount of substance' as only mole, or warrant creating terms such as [[amount concentration]] or [[amount fraction]] and using these uniquely? [[User:Bruce Bathurst|Geologist]] ([[User talk:Bruce Bathurst|talk]]) 19:36, 30 September 2009 (UTC) END NOTE]
+One may use amount of substance, mass, & volume to create any secondary dimension or any unit one finds convenient. One need not exclusively use moles (and mole fractions). Some units, such as molarity, ppm, ppb, &c, are invariant in being the quotient of n<sub>i</sub> and V. These, for an unknown reason, were described as being the same [[amount concentration]] by the SI. I can't imagine using it.
-We are mis-communicating. Let's see what the Wikipedia has on [[Ideal gas law]]:
-''
-The state of an amount of gas is determined by its pressure, volume, and temperature. The modern form of the equation is:''
+One may wonder why the SI chose a theoretical term, 'mole'. My guess would be that all other expressions for the concept of an amount of a substance contain secondary or derived quantities. The other reason may be that this need not be a theoretical term. The number of grams to choose for the amount of one mole of carbon can be deduced from assigning 1 to H, and using chemistry to complete the periodic table. Atomic theory need not be assumed.
-    pV = nRT,
+This arbitrary term 'amount of substance', chosen to describe the fundamental quantity 'mole', doesn't really deserve, IMO, this very lengthly exposition that apparently did not clarity a concept that was actually trivial.
-''where p is the absolute pressure of the gas; V is the volume of the gas; n is the amount of substance of the gas, usually measured in moles; R is the gas constant (which is 8.314472 JK−1mol−1 in SI units[4]); and T is the absolute temperature.''
+Below are responses to my queries about why I could no longer express the amount of Pb by its mass. Physchim62 clearly misunderstood my confusion, and I his. I suggest the article be severely curtailed, and [[amount concentration]] & [[amount fraction]] either deleted or kept contained within this article. They are being misunderstood elsewhere as replacements for [[molarity]] & [[mole fraction]].
-(First, of course, the ideal gas is not a gas; and second, only two variables are needed to determine the state of an amount of gas (Duhem's theorem).) To the point, why be redundant? Why say 'usually measured in moles'? I should be able to write PV = mRT, where m = any amount of substance. Because mass & volume are now excluded as measures of 'amount of substance', this should do.
+The digressions on the ideal gas model, melting-point depression, and osmotic pressure confused me into thinking Physchim62 was explaining why it was convenient to use the theory-laden term 'mole'.
-Cookbooks will, of course, have to be rewritten. Not just American ones (which measure by volume), but British ones (which measure by mass).
+[[Special:Contributions/67.91.218.205|67.91.218.205]] ([[User talk:67.91.218.205|talk]]) 01:20, 1 October 2009 (UTC)
-Physics and chemistry are, in my definitions, the only physical sciences. Hundreds of fields, including all the natural sciences, depend upon their journals. One should strive to express oneself clearly and avoid ambiguity. Concentration used to be measured in molarity, molality, mole fraction, or mass fraction, ppm, ppb, ppt, &c, depending upon its measurement or its use. Now, to simplify science, all but mole fraction are excluded. This change is just so we can write 'amount concentration' or 'amount fraction' rather than 'mole fraction'. (Ironically, there are fewer letters in 'mole' than 'amount'.)
+:The usual version of the [[ideal gas law]] is ''pV''&nbsp;=&nbsp;''nRT'', where ''n'' is the amount of substance in the system (as defined in this article). You could rewrite the ideal gas law as ''pV''&nbsp;=&nbsp;''NkT'', where ''N'' is the number of molecules, but you run into a problem: how do you count the number of molecules?
-Microsoft once tried to copyright the word 'window', so I couldn't use in when discussing emacs, curses, or smalltalk. This appears to me exactly what some august body is attempting to do. Terminology, sometimes codified in glossaries, follow the rules of lexicography: they may prescribe spelling, grammar, & syntax (as stated in the Wikipedia); but they are supposed to ''describe'' diction, giving examples taken from the literature. I have never seen, in my reading of 150 years of thermodynamic literature, the requirement that 'amount of substance' be expressed in moles. The earlier literature doesn't do this because the atomic theory was not yet in common use, and 'mole' is a theoretical term, dependent upon atomic theory.
+:The concept of amount of substance comes about because we can easily find physical relationships which depend on the number of molecules, such as [[melting-point depression]] or [[osmosis]], but we don't measure the number of molecules directly, merely a ratio of numbers of molecules in different samples. Electrical measurements are exactly analogous: we know that electric current is a certain number of electrons per second, but we don't know exactly how many. Electric charge at the macroscopic scale is measure in coulombs and not as a multiple of the elementary charge. Amount of substance at the macroscopic scale is measured in moles and not in numbers of molecules. The distinction arises from ''how we measure'' these quantities, it is not artificial at all.
-''
-*I see no reason why Wikipedia should chose to prefer your point of view that amount of substance is an artificial definition over and above the views of the various professional bodies which state otherwise.''
+:I see no reason why Wikipedia should chose to prefer your point of view that amount of substance is an artificial definition over and above the views of the various professional bodies which state otherwise. [[User:Physchim62|Physchim62]] [[User talk:Physchim62|(talk)]] 12:01, 29 September 2009 (UTC)
-(1) Perhaps the Wikipedia shouldn't slavishly obey professional bodies that prescribe statements in the Bible to be science, or (2) prescribe pi to be exactly 3, to simplify math for students, as a US State Legislature once did. Prescribing 'amount' rather than 'moles', and 'amount concentration' & 'amount fraction' rather than mole fraction (3) prevents us from defining an amount of lead by its weight: I must instead specify an arbitrary formula unit and the number of moles of these. (4) I can no longer specify the amount of water in a scored flask by its volume, room pressure & temperature. I must choose an arbitrary formula unit and specify the number of moles. (5) I can write a paper and specify 'amount concentration' or 'amount fraction' without ever stating that these are really mole fractions anywhere.
+...Many paragraphs removed by writer.
-'Amount substance' is an artificial definition because it was chosen arbitrarily among the various measures of amounts of substances already in use. It is a theoretical term because it depends upon atomic theory. To the contrary, I see no balances calibrated in moles, no flasks with 'mole' scribed on them. The atomic theory is not needed for melting-point depressions or osmotic pressure measurements: an empirical rule or bit of theory is. If it were, would this make any difference?
+We are mis-communicating. [[Special:Contributions/67.91.218.205|67.91.218.205]] ([[User talk:67.91.218.205|talk]]) 01:20, 1 October 2009 (UTC)
-If one wishes to choose this definition of the amount of something, people should change [[Amount concentration]] to point to [[Mole fraction]] rather than [[Molar concentration]]. The Wikipedia, IMO, needs to read the original proposal and carefully decide whether it wishes to follow it. [[User:Bruce Bathurst|Geologist]] ([[User talk:Bruce Bathurst|talk]]) 19:04, 30 September 2009 (UTC)
 :The power to "carefully decide whether it wishes to follow it" implies the power to carefully decide whether it wishes to ignore it. I shall take the latter route, thank you. [[User:Physchim62|Physchim62]] [[User talk:Physchim62|(talk)]] 19:52, 30 September 2009 (UTC)