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WHAT is a mole?

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Reply 20
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p29
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Original post by 1010marina
Kind of, but backwards:

All the mass numbers on the periodic table are in relation to carbon 12. They're all relative numbers, which means, they're unitless - if carbon 12 weighs 12 x (x could be grams, kilograms, etc.) then your hydrogen atom will weigh only 1 x. It's a relationship.

Avogadros number makes calculations using this fact easier. We measure in grams so we need a way of finding out how much 'stuff' is in a gram.

so if carbon weighed 24g would lead weigh 414- why are all mass numbers on the periodic table in relation to carbon 12?
Original post by p29
plz explain, explanations on google have led to this question.....


Dunno if this will help, but I'll try to explain! A mole is an amount, like a dozen.

Where a dozen of something means 12, a mole of something means 6.02x10^23.

That number is specifically chosen so that 1 mole of a given element weighs the same (in grams) as that element's mass number.

So 6.02x10^23 atoms of Carbon-12 weighs 12 grams, 6.02x10^23 atoms of Uranium-235 weighs 235 grams.
Original post by p29
so if carbon weighed 24g would lead weigh 414- why are all mass numbers on the periodic table in relation to carbon 12?



As explained, the masses on the periodic table are *relative*If you want to make a relative scale you have to choose something to define as your base unit. It just so happens that the base unit for atomic masses is defined as 1/12 of the mass of a carbon-12 atom
A butt-load of molecules.

the number is like 2300000000000000000000

but you don't need to remember it, it's called the Avogadro Constant and you will be given it in exams.

Some important notes are:

-A Mole of anything in a gaseous state will take up 24 litres of volume

-The chemical mass of every element you see on the periodic table is the number of grams in one mole of that chemical. i.e: Hydrogen has a mass of 1 so 1 Mole of Hydrogen weights 1 gram


Finally: Watch out for when it's used as a measure of concentration because you will often hear teachers say "add 2 moles of Hydrochloric Acid" or whatever, they are actually meaning mol/dm or moles per litre. That is a different figure which basically says how many moles can be found in one litre of that substance
Reply 24
Avatar for alow
alow
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Original post by JavaScriptMaster
A butt-load of molecules.

the number is like 2300000000000000000000


No it isn't


-A Mole of anything in a gaseous state will take up 24 litres of volume


At T=298K, P=101kPa.


-The chemical mass of every element you see on the periodic table is the number of grams in one mole of that chemical. i.e: Hydrogen has a mass of 1 so 1 Mole of Hydrogen weights 1 gram


1 mol of 1H weighs 1 gram.


Finally: Watch out for when it's used as a measure of concentration because you will often hear teachers say "add 2 moles of Hydrochloric Acid" or whatever, they are actually meaning mol/dm or moles per litre. That is a different figure which basically says how many moles can be found in one litre of that substance


Moles are not a measure of concentration, molarity is. Moles should never be used to express a concentration, what you should say is "Add 100ml of 2 molar hydrochloric acid".
(edited 7 years ago)
Original post by p29
plz explain, explanations on google have led to this question.....


Are you doing GCSEs? Are you studying triple science??
Reply 26
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p29
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Original post by *Alisha*
Are you doing GCSEs? Are you studying triple science??


Finished GCSE chemistry, i'm going to do A-level chemistry this september.
Reply 27
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alow
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Original post by p29
Finished GCSE chemistry, i'm going to do A-level chemistry this september.


Okay.

Can you define these terms for me: element, isotope, mass number, atomic number?
Reply 28
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p29
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Original post by MexicanKeith
Dunno if this will help, but I'll try to explain! A mole is an amount, like a dozen.

Where a dozen of something means 12, a mole of something means 6.02x10^23.

That number is specifically chosen so that 1 mole of a given element weighs the same (in grams) as that element's mass number.

So 6.02x10^23 atoms of Carbon-12 weighs 12 grams, 6.02x10^23 atoms of Uranium-235 weighs 235 grams.

thanks, this has been the clearest response I have gotten on here.
Reply 29
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alow
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Original post by FailedMyMocks
Ha. No more Chemistry for me! :smile:


Huh?
Original post by alow
Huh?


I dropped it..
Reply 31
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alow
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Original post by FailedMyMocks
I dropped it..


Good for you. Why post that here?
A mole is an amount (6.02*10^23).

The mass of 1 mole of atoms is the same as the atomic number in grams.
Reply 33
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p29
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Original post by FailedMyMocks
Ha. No more Chemistry for me! :smile:

hahaha, why did you drop it?
What alow said. He's like the king of chemistry.
Original post by alow
Good for you. Why post that here?


Just felt like adding it in :smile:
Original post by p29
hahaha, why did you drop it?


Not worth the effort. I didn't need it. Was pressured to take it..

Dropped both Chem and Bio. My life will undoubtedly be a lot easier..
Original post by cbreef
A little animal that lives in the ground :toofunny:


Alternatively it could be a patch of melanocyte cells on your skin that form a dark coloured patch :laugh:
Reply 38
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p29
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Original post by FailedMyMocks
Not worth the effort. I didn't need it. Was pressured to take it..

Dropped both Chem and Bio. My life will undoubtedly be a lot easier..


what do you want to study at uni?
Original post by p29
what do you want to study at uni?


Maths W/Finance or Computer Sci..

:biggrin:

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