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Redefining the Mole

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Re: Redefining the Mole

#21

Post by WilliamEdward »

apo wrote: post #18

On November 16, 2018, representatives from more than 50 countries are expected to make history when they gather in Versailles, France, to vote on redefining the SI, including the mole. The vote will close the book on this chapter of Vocke and Rabb’s work, but will open a new chapter in chemistry as the fundamental unit, for that branch of science will no longer be tied to a physical object but a constant of nature. I…

>If you're good with money, you should be good at chemistry.

I don't think it's quite that simple, but I can see where you're coming from.

Re: Redefining the Mole

#22

Post by nkrisc »

a1369209993 wrote: post #12
jpallen wrote: post #7

Earlier quoted context omitted.

It's an arbitrary number, but it's nice because one mole of atoms with atomic mass number X will weigh approximately X grams. This is exactly true for carbon-12 (and is what defines a mole).

> one mole of atoms with atomic mass number X will weigh approximately X grams Speaking as someone who has had to deal with rounding errors in floating-point graphics, data structure layouts, and real estate cartography, that sounds horrifying and insane.

Also consider you're unlikely to have a 100% pure sample of whatever it is you're measuring anyway, at least if it's a large enough sample to hold in your hand.

Approximations are still useful, even if they're not good enough for all applications.

Re: Redefining the Mole

#23

Post by zeveb »

jpallen wrote: post #7
rasteau wrote: post #5

> In practical terms, the mole helps chemists measure stuff. It helps express the amounts of atoms or molecules in a chemical reaction. Cause a half-mole of oxygen molecules (O2) to react with a mole of hydrogen molecules (H2) and you get a mole of water (H2O)—equal to about 18 grams of substance. Every example I find describing the utility of the mole could just as plausibly substitute "dozen" or "googol" for "mole"…

It's an arbitrary number, but it's nice because one mole of atoms with atomic mass number X will weigh approximately X grams. This is exactly true for carbon-12 (and is what defines a mole).

But that's a circular definition; one could use a different unit than grams (e.g. grains) and get a different pseudo-mole and hence a different pseudo-Avogadro's number.

Re: Redefining the Mole

#24

Post by apo »

WilliamEdward wrote: post #21
apo wrote: post #18

On November 16, 2018, representatives from more than 50 countries are expected to make history when they gather in Versailles, France, to vote on redefining the SI, including the mole. The vote will close the book on this chapter of Vocke and Rabb’s work, but will open a new chapter in chemistry as the fundamental unit, for that branch of science will no longer be tied to a physical object but a constant of nature. I…

>If you're good with money, you should be good at chemistry. I don't think it's quite that simple, but I can see where you're coming from.

I should have qualified that with "General Chemistry." You can solve the majority of General Chemistry problems by looking at them from an accounting perspective.

Neither units of money nor atoms can be created or destroyed. We use math to figure out what happened in a transaction or reaction.

Still, I'm curious - where do you see a fundamental divergence between the two?

Re: Redefining the Mole

#26

Post by SamBam »

pbhjpbhj wrote: post #19
bluenose69 wrote: post #8

Re the educational aspect -- when I ask students in my university class whether they remember Avogadro's number from high school, they all respond in the affirmative. When I ask them for the mantissa, the whole class sings out "6.02". Great! But, when I ask for the exponent, they are really quite uncertain. For many, the rote learning has cut off after the "times ten to the" in the sentence. This is disappointing, bu…

6E23! It rhymes. If they can remember "6E" and that it rhymes, then the first number after 3 they come to that rhymes is 23. Atoms in 1g Of 12C? It's 6E 23.

...in 12g, surely?

Re: Redefining the Mole

#27

Post by SamBam »

JoeAltmaier wrote: post #14
thrower123 wrote: post #13

Earlier quoted context omitted.

I remember that there is such a thing, and the relation between the number of molecules and a gram. But the exact number? No way - that's just not useful information to keep in my head post junior year chemistry. I've never had cause to need that information, especially when it is a google away.

That's kind of a self-fulling prophesy or something. Not having knowledge about something means, we work around it, fake it or just ignore it. For instance you might have wondered how much weight you lose with each breath. Converting O2 to CO2 means you're losing some mass of carbon each exhalation and that's a major channel for weight loss. But not remembering much about chemistry, nothing comes of this. Another par…

> means you're losing some mass of carbon each exhalation and that's a major channel for weight loss.

Indeed, that's almost 100% of weight loss, except for some daily fluctuations like water weight and what happens to be inside your gut at the moment, right? That's virtually the only way that body actually loses its own mass.

Re: Redefining the Mole

#28

Post by SamBam »

zaarn wrote: post #11
sesqu wrote: post #10

Earlier quoted context omitted.

The article does briefly discuss a slightly more accurate version of that definition, and why it's bad (it's convoluted and relies on the poorly-defined kilogram).

The kilogram will get a better definition this year if nothing holds it up (atleast, redefining it based on the planck's constant is planned for the 2018 meeting according to WP).

Right, that's a main point of the article.

Re: Redefining the Mole

#29

Post by JoeAltmaier »

SamBam wrote: post #27
JoeAltmaier wrote: post #14

Earlier quoted context omitted.

That's kind of a self-fulling prophesy or something. Not having knowledge about something means, we work around it, fake it or just ignore it. For instance you might have wondered how much weight you lose with each breath. Converting O2 to CO2 means you're losing some mass of carbon each exhalation and that's a major channel for weight loss. But not remembering much about chemistry, nothing comes of this. Another par…

> means you're losing some mass of carbon each exhalation and that's a major channel for weight loss. Indeed, that's almost 100% of weight loss, except for some daily fluctuations like water weight and what happens to be inside your gut at the moment, right? That's virtually the only way that body actually loses its own mass.

Chemistry gives your kidneys things to eliminate along with urine too?

Re: Redefining the Mole

#30

Post by syrrim »

jpallen wrote: post #7
rasteau wrote: post #5

> In practical terms, the mole helps chemists measure stuff. It helps express the amounts of atoms or molecules in a chemical reaction. Cause a half-mole of oxygen molecules (O2) to react with a mole of hydrogen molecules (H2) and you get a mole of water (H2O)—equal to about 18 grams of substance. Every example I find describing the utility of the mole could just as plausibly substitute "dozen" or "googol" for "mole"…

It's an arbitrary number, but it's nice because one mole of atoms with atomic mass number X will weigh approximately X grams. This is exactly true for carbon-12 (and is what defines a mole).

>"how is the mass number defined?"

>"that's easy! we take the mass of one mole of atoms, and that's the mass number!"

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