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Author Topic: Moles  (Read 606 times)

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blokeybloke

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Moles
« on: December 05, 2018, 07:19:55 PM »

How does “one mole of potassium” differ from “one mole of potassium atoms”? Do we interpret the former differently to the latter? Because aren’t moles counting units like “dozen”? So how exactly does the former make sense?
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DrCMS

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Re: Moles
« Reply #1 on: December 05, 2018, 10:48:20 PM »

In that example there is no difference but if you'd asked about hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine or iodine instead of potassium there would be a difference.
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blokeybloke

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Re: Moles
« Reply #2 on: December 06, 2018, 12:01:43 AM »

In that example there is no difference but if you'd asked about hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine or iodine instead of potassium there would be a difference.

Thanks for the response. But why is there no difference between the two for potassium? But not for the other elements?
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chenbeier

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Re: Moles
« Reply #3 on: December 06, 2018, 12:19:03 AM »

Potassium can react

K => K+ +e-

One mole potassium metal can be converted to the potassium ion. The amount is the same , also 1 mole.

Hydrogen H2 can go to the ions in this way:

H2 => 2 H+ + 2 e-. One mole hydrogen gives 2 mol hydrogen ions.
« Last Edit: December 06, 2018, 02:20:53 AM by chenbeier »
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mjc123

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Re: Moles
« Reply #4 on: December 06, 2018, 02:14:56 AM »

Strictly (though this is another thing about which usage can be loose) a mole is an amount of substance, not a number of things. A mole is that amount of substance that contains Avogadro's number NA of basic units (atoms, molecules, ions etc. as appropriate). 1 mole of potassium contains NA K atoms; 1 mole of potassium chloride contains NA K+ ions and NA Cl- ions. 1 mole of hydrogen gas contains NA H2 molecules, and therefore 2NA H atoms.
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Borek

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Re: Moles
« Reply #5 on: December 06, 2018, 03:10:45 AM »

One mole potassium metal can be converted to the potassium ion.

Nope, pay attention to wording.

One mole of metallic potassium can be converted to one mole of potassium ions. What you wrote suggests one mole of metallic potassium can be converted to a single cation, which is completely off.
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blokeybloke

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Re: Moles
« Reply #6 on: December 06, 2018, 03:22:31 AM »

Strictly (though this is another thing about which usage can be loose) a mole is an amount of substance, not a number of things. A mole is that amount of substance that contains Avogadro's number NA of basic units (atoms, molecules, ions etc. as appropriate). 1 mole of potassium contains NA K atoms; 1 mole of potassium chloride contains NA K+ ions and NA Cl- ions. 1 mole of hydrogen gas contains NA H2 molecules, and therefore 2NA H atoms.

Hey mjc I prefer to think of the mole as an amount of substance as well rather than as a number of things. But then this raises the question of why I see “one mole of water molecules” or “one mole of sodium atoms” constantly in chemistry texts.
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chenbeier

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Re: Moles
« Reply #7 on: December 06, 2018, 04:15:16 AM »

One mole potassium metal can be converted to the potassium ion.

Nope, pay attention to wording.

One mole of metallic potassium can be converted to one mole of potassium ions. What you wrote suggests one mole of metallic potassium can be converted to a single cation, which is completely off.

Sorry you took my sentence out of the context. Not nice.

I wrote
Quote
One mole potassium metal can be converted to the potassium ion. The amount is the same , also 1 mole.

I took attention to the mole.  I am not a native english speaker. If it is a problem of the correct englisch sentences.
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Borek

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Re: Moles
« Reply #8 on: December 06, 2018, 11:54:39 AM »

Yes, it can be a problem with the translation, but splitting the sentence into two in such a way is confusing.
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-_-zzzz

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Re: Moles
« Reply #9 on: December 08, 2018, 03:10:48 AM »

How does “one mole of potassium” differ from “one mole of potassium atoms”? Do we interpret the former differently to the latter? Because aren’t moles counting units like “dozen”? So how exactly does the former make sense?

Despite the fact that we can interpret the two sentences differently in this context they mean the same thing because the only constitutive units of potassium are potassium atoms. In the case of diatomic elements however it is different. For example saying “one mole of hydrogen” is ambiguous because do we mean one mole of hydrogen atoms or one mole of hydrogen molecules? Any hypothetical sample of hydrogen can have various constitutive particles so we need to be specific. Hope this helped.
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