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Topic: Moles  (Read 521 times)

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Offline Sutchannn

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Moles
« on: September 08, 2020, 11:35:30 AM »
(School module question)

If the average galaxy has approximately 150 bilion stars, and if astronomers estimate that the universe has atleast 125bilion galaxies, how many moles of stars are in the universe?


(Thank you so much, and can i see your solutions for me to undsrstand?)
« Last Edit: September 08, 2020, 11:54:19 AM by Sutchannn »

Offline AWK

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Re: Moles
« Reply #1 on: September 08, 2020, 11:47:06 AM »
IUPAC definition - The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 × 1023 elementary entities.
Stars are not elementary entities.
AWK

Offline sjb

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Re: Moles
« Reply #2 on: September 08, 2020, 01:46:05 PM »
A looser definition might just be that number of entities. So, how many stars do you have? Your final answer may depend considerably on your location.

Offline Corribus

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Re: Moles
« Reply #3 on: September 08, 2020, 02:53:34 PM »
This seems relevant: A mole of moles
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline MNIO

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Re: Moles
« Reply #4 on: September 08, 2020, 02:59:27 PM »
125x109 galaxies      150x109 stars         1 mole stars
--------------------- x ----------------- x --------------------- = 0.031 moles of stars / universe
      1 universe           1 galaxy              6.022x1023 stars
« Last Edit: September 08, 2020, 04:11:27 PM by MNIO »

Offline Meter

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Re: Moles
« Reply #5 on: September 09, 2020, 12:39:46 AM »
You can always use Avogadros constant (NA ~= 6.022 * 20 23 mol-1) to convert moles to a mole quantity. (look at the units)

Offline MNIO

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Re: Moles
« Reply #6 on: September 09, 2020, 02:49:30 PM »
IUPAC definition - The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 × 1023 elementary entities.
Stars are not elementary entities.

NOT true.  Stars ARE elementary entities if that's how you define your elementary entities.  This is covered in EVERY general chemistry textbook and every general chemistry class. You should know this by now.
« Last Edit: September 09, 2020, 03:12:31 PM by MNIO »

Offline AWK

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Re: Moles
« Reply #7 on: September 09, 2020, 03:42:41 PM »
IUPAC Goldbook (last revision March 30,  2020)
The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76×1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol-1, and is called the Avogadro number.
The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.


This definition applies to all chemists.
AWK

Offline MNIO

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Re: Moles
« Reply #8 on: September 09, 2020, 04:08:18 PM »
Why are you arguing with me on this point?

*********
The IUPAC link for your source is
  https://goldbook.iupac.org/terms/view/M03980
if you click on the "source" link at the end it takes you to this
  https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-EN.pdf
page 134 is verbatim of your link with this additional sentence your online link left off...
  "The effect of this definition is that the mole is the amount of substance of a system that
  contains 6.022 140 76 × 1023 specified elementary entities."
page 172 states
  When the mole is used, the elementary entities must be specified and MAY BE atoms,
  molecules, ions, electrons, other particles, or specified groups of such particles.

Clearly you can see the words "specified elementary entities" and "elementary entities must be specified" and "may be" right there in black and white (and red).  The meaning of this definition is (1) after you specify the elementary entity, then (2) 1 mole of those entities = 6.02214076x10^23 entities.  NO where in either of those links or any chemistry literature anywhere does it say "for the definition of moles, the term elementary entities IS LIMITED TO atoms, electrons, protons, etc". 

Furthermore, the IUPAC update you're referencing is related to Avogadro's number as based on a fixed numerical value rather than the the number of atoms in 0.012kg of C-12 atoms.  1 mol is still Avogadro's number of "specified elementary entities"

it's like you're arguing.. "all bakers may only use the term dozen only when referencing 12 eggs or 12 cookies.  Dozen cannot be used for donuts, bagels, loaves of bread or by non-bakers for anything else"  And then giving a reference that says "in the past we based dozen on the number of cookies in exactly 12g of 1g chocolate chip cookies.  Now we're basing it on the number 12". 

Again.. this is covered in EVERY general chemistry textbook in use today.  Everyone who completes gen chem sees this material.  I read your response and shake my head wondering... why would you argue this ridiculous point?  Maybe you can explain that one.
« Last Edit: September 09, 2020, 05:58:35 PM by MNIO »

Offline Corribus

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Re: Moles
« Reply #9 on: September 09, 2020, 06:26:22 PM »
AWK, the IUPAC definition, like all IUPAC definitions, is generally concerned with applications relating to chemistry. This doesn't mean that concepts defined by IUPAC cannot be extended to non-chemical systems. Even beyond that, the IUPAC definition does not strictly define what a "particle" is. The mole concept is commonly extended to nanoparticles, microparticles, etc., although I don't love it, because I find it to be a little ambiguous at times. Nevertheless, if we are willing to accept the notion of "particles" being merely a countable and mathematically homogeneous objects, then there's no reason the IUPAC definition cannot be extended to any macroscopic (or very macroscopic) thing. Although stars probably wouldn't be considered a particle in any chemical or physical sense, they are countable objects. So even though it may be a loose interpretation of what a particle is, the mole concept could be extended to stars.

Btw: MNIO, in the future, please don't just give the OP a solution to a problem. We try to help students work the problems out themselves. That's how they learn. And maybe tone down the aggression a notch, eh? This is supposed to be a friendly, professional environment.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline MNIO

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Re: Moles
« Reply #10 on: September 09, 2020, 09:42:55 PM »
Corribus.

As you can probably tell, I'm thoroughly annoyed at all the constant and arrogant bickering on this site.  When a student asks for help with a relatively simple chemistry question and the first response is an arrogant attack on the question / questioner, that's not very professional is it?  When a few posts later someone actually shows how to solve the problem and the members here break down into an insane quarrel, that's not very professional either is it? Does it really add to the students learning to read a discussion about who thinks moles should be used exclusively by chemists to atoms, molecules and electrons and not others? Or whether or not Stars are entities?

Seriously, I've spent my entire adult life studying, developing my expertise, and working in the chemical / chemical engineering fields.  For literally decades, I've dedicated what little free time I have to help students learn the concepts and get them thinking about how to solve problems.  I came here to this site after reading some of responses to students and thinking that maybe I could lend a hand and help out.  My mistake.

In this case, I gave the complete answer to (1) demonstrate how to setup this dimensional analysis problem and (2) quickly end the discussion of whether or not mole can be applied to "stars".  My mistake as the argument continues.  My mistake as I've received warnings for providing the answer here and as I am currently being "watched" by the moderators.  Now I'm being lectured on "professionalism".

However you might view it, clearly my skills and expertise are simply not wanted here.  Your longer term members don't need another experienced "professional" helping out.  Your guys have all the answers.  Everything from "how would you do solve it" to "that question should not have been asked".  Useful stuff.  Especially to beginning gen chem students struggling to understand "moles". 

You don't need to respond.  I've left the site. 


Offline Borek

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Re: Moles
« Reply #11 on: September 10, 2020, 03:16:18 AM »
IUPAC Goldbook (last revision March 30,  2020)
The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76×1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol-1, and is called the Avogadro number.
The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.

If only IUPAC was consistent.

http://goldbook.iupac.org/terms/view/E02033#:~:text=Any%20countable%20object%20or%20event,Cite%20as%3A%20IUPAC.

elementary entity
Any countable object or event, but usually a molecule, an ion or a specified group of atoms.
« Last Edit: September 10, 2020, 03:27:24 AM by Borek »
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Offline chenbeier

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Re: Moles
« Reply #12 on: September 10, 2020, 04:34:48 AM »
In my opinion ,stars cannot be counted in mole, because for the mol it should be the same atom, molecule, compound. But stars made by different compounds, they are not equal. The earth is different from Mars, Venus, etc. Maybe it would work with the sun and the other fix stars,  what mean mainly H2, He inside.

Offline AWK

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Re: Moles
« Reply #13 on: September 10, 2020, 05:40:39 AM »
The star is not a substance.

The authors of the new version of the SI system noticed this extending use of the concept of a mole and additionally introduced the concept of Avogadro number (numerical coefficient). In my opinion, as a number, The Avogadro number can be used anywhere in the world of large numbers (e.g. in biology to compare the numbers of cells, bacteria or viruses, in material science to determine the number of nanoparticles, even to count stars, although the authors of the SI System define this number only as interpreted by physicists and chemists.
You can always change the definition, but it will be agreed as scientists that appropriate representative bodies do it after careful consideration of the consistency of the system.
AWK

Offline Corribus

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Re: Moles
« Reply #14 on: September 10, 2020, 08:31:07 AM »
In my opinion ,stars cannot be counted in mole, because for the mol it should be the same atom, molecule, compound. But stars made by different compounds, they are not equal. The earth is different from Mars, Venus, etc. Maybe it would work with the sun and the other fix stars,  what mean mainly H2, He inside.
I understand your view, but moles are frequently used to count particles, and particles are never truly homogeneous, in either composition or morphology. This is why I said "mathematically equivalent" above.

I mean, we can say, "there are 50 people in a room" and we don't lose sleep over it, even though every person is different. This is because we use "person" as a term of classification, not as an infinitely precise descriptive term, and so every person is counted the same way. (By the same token, we wouldn't include the five plants in the room, because we recognize that plants aren't people. We do the same thing when counting moles of something, we classify them as belonging to the category or not, and then count.

You just have to be a little careful when translating other concepts associated with moles (such as molecular weight) if you're using moles to count objects that aren't truly identical. Thankfully we get around it - we have no problem expressing molecular weight of polymers, even though the molecular weight is variable.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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