Can "mole" unit only be integer values?

In summary, the concept of a mole is based on Avogadro's number, which states that 1 mole has 6.023*10^23 particles. It is possible to talk about moles in a non-integer sense, such as 1/2 mole or 1/10 mole. However, due to the huge number of particles in 1 mole, it is not possible to measure individual atoms and the number of particles in a mole is always an approximation. There have been proposals to redefine the mole as an integer number, but no agreement has been reached yet. Additionally, there have been attempts to redefine the kilogram in terms of atoms or fundamental constants, but no consensus has been reached. The mass of the
  • #1
pyroknife
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I am confused about the concept of a mole. Avogadro's # says that 1 mole has 6.023*10^23 particles.
Does it make sense to talk about moles in a non-integer sense?
For example, can you say that 1/2 mole has 1/2*(6.023*10^23) particles?
 
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  • #2
pyroknife said:
I am confused about the concept of a mole. Avogadro's # says that 1 mole has 6.023*10^23 particles.
Does it make sense to talk about moles in a non-integer sense?
For example, can you say that 1/2 mole has 1/2*(6.023*10^23) particles?

Yes, you can certainly talk about 1/2 mole, which has 3.0115*10^23 particles, or 1/10 mole, which has 6.023*10^22 particles, or 1/1000 mole, which has 6.023*10^20 particles. Perhaps your confusion lies in the fact that you must have an integer number of particles. But Avogadro's number is so huge, that you cannot resolve it down to the level of individual atoms. To do this, you would have to tell the difference between the number:
602,300,000,000,000,000,000,000
and the number:
602,300,000,000,000,000,000,001
No measuring device is that precise. So you are always talking about an approximate number of particles.
 
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  • #3
Actually there is a proposal to redefine mole to be an integer number.

Technically it IS an integer number even now, as it is "number of atoms in exactly 12 g of C-12". We are just limited by the accuracy with which we can define and measure mass.
 
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  • #4
pyroknife said:
I am confused about the concept of a mole. Avogadro's # says that 1 mole has 6.023*10^23 particles.
Does it make sense to talk about moles in a non-integer sense?
For example, can you say that 1/2 mole has 1/2*(6.023*10^23) particles?
Now, if you'd like to volunteer to count the number of atoms in 12 g of carbon ...
 
  • #5
Didn't they try to redefine 1kg as a certain and exact amount of atoms?
 
  • #6
fresh_42 said:
Didn't they try to redefine 1kg as a certain and exact amount of atoms?
That's just one proposed method for defining the kilogram:

https://en.wikipedia.org/wiki/Kilogram

See the section on "Atom Counting"

There are other proposals for defining the kilogram in terms of certain fundamental constants, like Planck's Constant, but no agreement has yet been reached by the international body in charge.
 
  • #8
SteamKing said:
Now, if you'd like to volunteer to count the number of atoms in 12 g of carbon ...
Well, by NIST standards Na = (6.0221415 ± 0.0000010) × 1023 units, provided that atomic mass of C-12 remains constant over time... but, of course it does not ... Interesting challenge.
 
  • #9
James Pelezo said:
provided that atomic mass of C-12 remains constant over time... but, of course it does not ...
What do you mean by that? If you are talking about the fact that the mass of the International Prototype Kilogram in Paris changes with time, this has nothing to do with the properties of 12C changing, but is simply related to the imperfections of an actual artifact.
 
  • #10
Even the number of particles can be non-integer, e.g. when you talk about statistics, so there is even less problem with the number of moles being non-integer.
 
  • #11
DrClaude said:
What do you mean by that? If you are talking about the fact that the mass of the International Prototype Kilogram in Paris changes with time, this has nothing to do with the properties of 12C changing, but is simply related to the imperfections of an actual artifact.

In this case, I can only reply to what I have read. The note specifically postulates that C-12 has changed with time, but, granted, it does not specify anything relating to properties of C-12 ... Here's the excerpt and reference...

These changes cannot be measured exactly, simply because there is no "perfect" reference against which to measure them—Le Gran K is always exactly one kilogram, by definition. It is estimated that Le Gran K may have changed about 50 micrograms—that is, roughly by about 150 quadrillion (1.5 × 1017) atoms—since it was constructed. This implies that by current measurement conventions, the mass of a single atom of carbon-12 is changing in time, whereas modern theory postulates that it remain constant.
http://www.americanscientist.org/issues/id.368,y.0,no.,content.true,page.1,css.print/issue.aspx

My apologies if I've misunderstood your point of issue.
 
  • #12
The key part of the quote is
James Pelezo said:
This implies that by current measurement conventions, the mass of a single atom of carbon-12 is changing in time,
The mass is apparently changing because the standard keeps changing as the IPK loses or gain some atoms as it is manipulated.
 
  • #13
James Pelezo said:
This implies that by current measurement conventions, the mass of a single atom of carbon-12 is changing in time, whereas modern theory postulates that it remain constant.
This is poorly worded. The mass of an atom is not changing over time. The mass of the kilogram prototype is changing over time. So as the mass of the kilogram changes the number of atoms per kilograms must change in order for the mass to remain constant.
 
  • #14
DaleSpam said:
This is poorly worded. The mass of an atom is not changing over time. The mass of the kilogram prototype is changing over time. So as the mass of the kilogram changes the number of atoms per kilograms must change in order for the mass to remain constant.
I'm confused by the wording of the underlined statement... 'as the mass of the kilogram changes the number of atoms per Kg must change => constant mass'? This sounds like a 'Yogi-ism'... 'If you come to a fork in the road, take it' ... confusing, huh? That is, how does the number of atoms changing result in a constant mass?
 
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  • #15
James Pelezo said:
I'm confused by the wording of the underlined statement... 'as the mass of the kilogram changes the number of atoms per Kg must change => constant mass'?
He means "as the mass of the kilogram prototype changes".
 
  • #16
OK, thanks... that makes more sense.
 

1. Can the mole unit have decimal or non-integer values?

No, the mole unit is a counting unit and is defined as the number of particles in 12 grams of Carbon-12. Therefore, it can only have integer values.

2. Why is the mole unit defined as an integer value?

The mole unit is defined as an integer value to make it easier to count and measure the amount of a substance. It also reflects the fact that matter is made up of discrete particles, such as atoms and molecules.

3. Can I convert decimal or non-integer values to moles?

Yes, you can convert decimal or non-integer values to moles by rounding the number to the nearest whole number. However, keep in mind that this may result in a slight error in the calculation.

4. Is the mole unit used in all branches of science?

Yes, the mole unit is a fundamental unit in chemistry and is used in all branches of science that deal with matter and its properties. It is also commonly used in fields such as biology, physics, and engineering.

5. Are there any exceptions to the mole unit being an integer value?

No, the mole unit is always an integer value. However, in some cases, it can be represented in scientific notation with decimal values, but this is just a different way of expressing the same integer value.

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