do not get the mole concept

[beachbum]

especially the thing when it refers to carbon all the time w./ the 1/12 amu thing. can anyone explain more thoroughly?

[Dak]

yup.

 

two molecules of H₂O will yield two molecules of H₂ and one molecule of O₂

 

one molecule is a very fiddley quantity to work with.

 

Basic maths: if two molecules of H₂O will yield two molecules of H₂ and one molecule of O₂, then two MILLION molecules of H₂O will yield two MILLION molecules of H₂ and one MILLION molecules of O₂. these are nicer, less fiddly quantities to work with. However, it now becomes a pain in the arse to wright down huge numbers each time.

 

so someone invented mols (horay!). mr avagadro was his name. a mole is simply x molecules, where x = very large number.

 

this makes the quantities easyer to work with, cos rather than having to weigh out one molecule of H₂O, you can weigh out x molecules, or one mol, of H₂O (which is a larger number and thus easyer to weigh out).

 

the ratios remain the same so its still true: eg, two molecules of H₂O will yield two molecules of H₂ and one molecule of O₂ --> 2x molecules of H₂O will yield 2x molecules of H₂ and x molecule of O₂ --> two mols of H₂O will yield two mols of H₂ and one mol of O₂

 

the reason carbon is mentioned all the time is that carbon-12 is used as a standard: the number of molecules in exactly 1g of carbon-12 is the number of molecules in a mole.

 

eg, 1g carbon-12 = x molecules carbon-12 = 1 mol carbon-12

 

and, for your information, x (ie, the number of molecules in a mol) = 6.02214199 × 10²³ = Avogadro's Constant.

 

as google will convieniently tell you <-- which i think is cool.

 

So, 2x(6.02214199 × 10²³) molecules of H₂O will give you 2x(6.02214199 × 10²³) molecules of H₂ and 6.02214199 × 10²³ molecules of O₂, which is simplified to 2mol H₂O --> 2 mol H₂ + 1 mol O₂, or simply

 

2H₂O --> 2H₂ + O₂

 

 

NOTE: not to be confused with molarity, or M. this is the concentration of acids, and is moles per liter.

 

so a 5M conc of H₂SO[/sub]4[/sub] would have a concentration of 5 mols per litre.

 

if your wondering, there are tables where you can look up the weight of one gram of a substance, so you know how much is nessesary for a reaction: eg, to make 5M H₂SO₄, youd look up the weight of 1 mol of H₂SO₄, times that weight by 5 and chuck that many gramms of H₂SO₄ into a litre of distilled water; et voila, 5M H₂SO₄.

[jdurg]

A mole is a counting unit. When you buy 12 doughnuts, do you say 'I want 12 doughnuts'? No. You say I want a dozen. A score, a couple, a pair, etc. are all counting units as well. A mole is the counting unit for 6.022x10^23 items. So a mole of cars would be 6.022x10^23 cars. If you have a general chemistry textbook, just look in the section about Avogadro's Number and the definition of a mole and it should become a lot clearer to you.

[Skye]

When you buy 12 doughnuts, do you say 'I want 12 doughnuts'? No. You say I want a dozen.

You only say that so you get a baker's dozen.

[akcapr]

a mole is just a certain number of atoms, since some atoms of elements are hevier or lighter than others, the weights of one mole of different elements weigh different amounts